Guide to World War II Hangars 03 - Type C Hangars

Transcription

1 Design and Maintenance Guide 24 Guide to World War II Hangars DEFENCE ESTATES MINISTRY OF DEFENCE WIND SENSITIVE STRUCTURES December 2001

2 Crown Copyright 2001 Published by the Ministry of Defence December 2001

3 Foreword This Guide was prepared under the patronage of HQ STC. This document is for the use of Top Level Budget Holders (TLBHs) for application by the Project Sponsors, Property Managers (PROMs), Establishment Works Consultants (EWCs), Works Services Managers (WSMs) and other parties connected with the hangar. For Projects, the principal users of the document are expected to be Project Sponsors to influence the preparation of the Statement of Requirements, the Project Manager and the designers and installers. In addition, for works services falling within the Property Management remit, the EWC assists the Property Manager in determining the description of task and the WSM is responsible for design, installation and maintenance. MOD addressees should ensure that designers and contractors employed for works connected with the Type C hangar are advised of this Guide. Amendments to this Guide will be advised by Defence Estates (DE) Technical Bulletin, issued to PROM and TLBH Works staff. It is the responsibility of the user to check with the PROM or Project Sponsor if amendments have been issued. There is a feedback form at Annex B, for suggested changes or developments to the document. A hangar notification form is also included at Annex C for feedback on any hangar related problems or works on a hangar building. Technical advice and assistance can be obtained from DE. Approaches may be through local DE offices or directly to the Focal Point: Wind Sensitive Structures Specialist Services Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL All enquiries in connection with drawings and requests for copies of drawings should be addressed to: Library (DE Information Management) Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL Information provided is for guidance only and it must be verified and checked for each individual project or works service. December 2001 i

4 Foreword Use of this Guide does not absolve a Project Manager or WSM from any responsibility relating to the design, neither does the existence of the Guide constrain the Project Manager or WSM from using alternatives, provided such alternatives can be demonstrated to provide a result of equal safety, quality and cost effectiveness. This Guide has been devised for the use of the Crown and its Contractors in the execution of contracts for the Crown. The Crown hereby excludes all liability (other than the liability for death or personal injury) whatsoever and howsoever arising (including, but without limitation, negligence on the part of the Crown, its servants or agents) for any loss or damage however caused where the Guide is used for any other purpose. Compliance with a DE Design and Maintenance Guide will not of itself confer immunity from legal obligations. ii December 2001

5 Acknowledgement December 2001 iii

6 Amendments Amendments Page No Date Inserted By iv December 2001

7 Abbreviations BS DCI DE DMG DWS EWC HQ STC JSP MHE MOD PM PROM TB WSM British Standard Defence Council Institution Defence Estates DE Design & Maintenance Guide Defence Works Services Establishment Works Consultants Headquarters Strike Command Joint Services Publication Mechanical Handling Equipment Ministry of Defence Project Manager Property Manager DE Technical Bulletin Works Services Manager December 2001 v

8 vi December 2001

9 Contents FOREWORD ACKNOWLEDGEMENT ABBREVIATIONS 1. INTRODUCTION 2. BACKGROUND 2.1 HISTORY OF TYPE-C HANGARS 2.2 USAGES TODAY 2.3 LOCATIONS OF EXISTING TYPE-C HANGARS 3. DESCRIPTION 3.1 IDENTIFICATION 3.2 DRAWINGS 3.3 MAIN STRUCTURAL ARRANGEMENTS 4. STRUCTURAL APPRAISAL 4.1 DESIGN PHILOSPHY 4.2 MEMBERS ANALYSED 4.3 BACKGROUND TO PERMISSIBLE STRESSES AND LOADING USED IN THE APPRAISAL 4.4 OUTCOME 4.5 CONCLUSION 4.6 IMPLICATIONS OF APPRAISAL CONCLUSION 5. OPERATIONAL REQUIREMENTS 5.1 INTRODUCTION 5.2 HANGAR BUILDING 5.3 PROFESSIONAL AND TECHNICAL INSPECTIONS 6. REFURBISHMENT GENERAL 6.1 INTRODUCTION 6.2 OPTIONS AND RECOMMENDATIONS 6.3 WARRANTIES/GUARANTEES 7. REFURBISHMENT ROOFING 7.1 DESCRIPTION 7.2 PROBLEMS 7.3 ROOFING REQUIREMENTS 7.4 ROOFING MATERIAL 7.5 ROOFING OPTIONS 7.6 DETAILED DESCRIPTION OF ROOFING OPTIONS 7.7 SUMMARY OF ROOFING OPTIONS December 2001 vii

10 8. REFURBISHMENT - GUTTERS AND DRAINAGE 8.1 DESCRIPTION 8.2 PROBLEMS 8.3 GUTTER PROPOSALS 8.4 GUTTER MATERIAL OPTIONS 8.5 GUTTER ARRANGEMENT 8.6 SNOWBOARDS 8.7 BELOW-GROUND DRAINAGE 9. REFURBISHMENT WINDOWS 9.1 DESCRIPTION 9.2 PROBLEMS 9.3 PROPOSAL FOR WINDOWS 10. REFURBISHMENT WALLS 10.1 DESCRIPTION 10.2 REINFORCED CONCRETE 10.3 DETERIORATION OF WALLS 10.4 ALTERATIONS 10.5 TREATMENT OF EXISTING CLADDING 10.6 PROPOSALS FOR SOLID WALLS 11. REFURBISHMENT DOORS 11.1 DESCRIPTION 11.2 PROBLEMS 11.3 DOOR OPTIONS 11.4 DOOR INSPECTIONS 11.5 HANGAR DOOR OUTRIGGERS 11.6 BLAST AND FRAGMENT PROTECTION 12. ROOF ACCESS 13. STANDARD AND REGULATIONS 13.1 BUILDING REGULATIONS 13.2 PLANNING AND FIRE OFFICER APPROVALS 13.3 CROWN FIRE STANDARDS 13.4 HEALTH AND SAFETY 13.5 PHYSICAL SECURITY 13.6 ENVIRONMENTAL LEGISLATION ANNEXES A B C D E F G H I RECORD DRAWINGS CHANGE SUGGESTION FORM HANGAR NOTIFICATION FORM BASIC WIND SPEED MAP SAFE LOADING ROOFING OPTIONS & DESCRIPTION OF ROOFING MATERIALS WINDOW REFURBISHMENT OPTIONS & TYPICAL WINDOW DRAWINGS DOOR REFURBISHMENT OPTIONS COST COMPARISONS REFERENCES viii December 2001

11 Guide To World War II Hangars 1 Introduction SCOPE The content of this Guide is applicable to works services and projects. It includes new build, maintenance and refurbishment work. In addition, the guidance relates to safe usage of the hangar and the operations within the structure and in its vicinity. This Guide is intended for use by: Property Managers (PROMs), Establishment Works Consultants (EWCs) and Works Services Managers (WSMs) Project Sponsors, Project Managers, design consultants and contractors users of a Type-C hangar and those engaged in duties connected with the hangar. MOD addressees should ensure that designers and contractors employed for works connected with the Type C hangar are advised of this Guide. This Guide is to be used to provide preliminary advice to assist in the preparation of Statements of Requirement, the undertaking of Option Studies and the preparation of Technical Briefs. It may also be used as the basis for Professional Appraisals as required by DE Specification 005. However, all works be they major repair, major refurbishment or demolition must be supported by an adequate site survey and appropriate assessments by competent engineers. SUMMARY OF CONTENT A description is given of the typical Type C hangar, how it can be identified, its typical structural form and features, drawings that have been prepared for a typical Type C hangar. Using archive drawings as a basis, CAD drawings have been prepared by DE to record the key features of a Type C hangar. A structural appraisal of the hangar has been carried out. This indicates that, generally, the hangars are adequate to cover current loadings provided moderate precautions are taken. Hangars in more exposed locations must be considered individually. Precautions must be taken for the safe undertaking of activities and operations within the hangar and in its vicinity. For example, heavy snowfall can apply excessive loading, due to snow infilling the valleys of the multi-pitched roof. In addition, high winds can necessitate closure of the hangar doors to reduce the effect of dominant openings. The safe use of doors is also addressed with regard to their operation, inspection and maintenance. December

12 Guide To World War II Hangars 1 Introduction The Guide covers hangar refurbishment and the common work items with which a PROM or Project Sponsor will become involved, eg. re-roofing, wall cladding and repair or renewal of doors and windows. Guidance is given in respect of MOD policy, working practices and other standards or codes. Typical solutions are given with illustrations for re-roofing and recladding the walls. Refurbishment options have been developed to include whole life costs. Therefore, the initial costs of the appropriate roofing or cladding solution have been considered in conjunction with subsequent maintenance and operational costs eg. those due to heating losses. The implications of applying the requirements of Crown Fire Standards are addressed where appropriate. MOD security matters are also discussed in the document. This Guide explains how the Type C structure was appraised, the design philosophy adopted and findings of the analysis. Historical design codes, steelwork stresses and the loading criteria are covered. With regard to wind loading, the significance of dominant openings in a hangar building due to doors and windows and the building's permeability is also explained. In summary, it is usually feasible to refurbish a Type-C hangar with practical, economical and attractive, economical solutions, rather than demolish and rebuild. Each hangar should be assessed on a site specific basis, because several factors influence a decision. These include local variations in snow and wind loading, local labour and materials costs, local planning restrictions for use of the building and the proposed life of the hangar. The Type C hangar with its open area of some 4180m² (45,000 sq ft) and a clear headroom for 1934 hangar of m (35'-4"), and for 1938 hangar of 9.246m (30'-4"), provides a functional and flexible working facility. With adequate routine maintenance and the careful consideration of major refurbishment options, particularly re-roofing, Type C hangars should continue to offer economic hangar accommodation for many years. Readers are reminded of the general duty to provide information on hangar related problems and hangar projects. A proforma is attached at Annex C. The information obtained from this process enables DE to disseminate relevant hangar related technical guidance. 2 December 2001

13 2 Background 2.1 HISTORY OF TYPE-C HANGARS The Type-C hangar is the most common of all MOD wartime hangars. In the order of 200 Type-C hangars are still in use on the MOD estate in the UK. With good maintenance and periodic refurbishment, many more years of service can be provided. The first Type-C hangars were constructed in the interwar RAF expansion period of the mid-1930's. The design evolved from the earlier type A and B hangars developed during the 1920's. Their construction continued until the early 1940's when, due to wartime commitments, the RAF needed hangars which could be built much faster, and so other types of hangar, mainly of a lighter construction, superseded the Type-C. 2.2 USAGES TODAY The predominant use today is still as aircraft accommodation. Many old airfields have now passed from the RAF to the Army, and the hangars continue to be used for other purposes such as motor transport, garaging and workshops, and the storage of equipment and materials. 2.3 LOCATIONS OF EXISTING TYPE-C HANGARS The list overleaf illustrates known locations of Type-C hangars on the MOD estate. It is believed, however, that the list is not complete and there are Type-C hangars at other locations. Some hangars listed may have been disposed of, either by demolition or through sale. However, the list is the best available at this time and is given for information purposes only. Establishments with Type C Hangar which are not included are requested to complete the form at Annex C and return to the Wind Sensitive Structures Section, Specialist Services at Sutton Coldfield. December

14 Guide To World War II Hangars 2 Background Locations of existing Type-C hangars 1 Abingdon, Dalton Barracks (1) 35 Locking, RAF (1) 2 Aldergrove, RAF (4)) 36 Lossiemouth, RAF (3) 3 Aston Down, PESD (1) 37 Manby (5) 4 Bassingbourn, Army (4)0 38 Marham, RAF (5) 5 Benson, RAF (4) 39 Middle Wallop, AAC (5) 6 Bicester, RAF (1) 40 Mildenhall, RAF (2) 7 Binbrook, RAF (5) 41 Molesworth, RAF (1) 8 Boscombe Down, DERA (1) 42 Netheravon Airfield (1) 9 Bramcote, RAF (5) 43 Newton, RAF (5) 10 Brize Norton, RAF (4) 44 Northolt, RAF (1) 11 Catterick, Army (2) 45 Odiham, RAF (3) 12 Church Fenton, RAF (2) 46 Scampton, RAF (4) 13 Coltishall, RAF (4) 47 Sealand, RAF (1) 14 Cosford, RAF (3) 48 Shawbury, RAF (4) 15 Cottesmore, RAF (4) 49 South Cerney, Army (2) 16 Cranwell RAF (2) 50 St Athan, RAF (4) 17 Debden, RAF (1) 51 St Eval, RAF (1) 18 Dishforth, Army & RAF (5) 52 Stradishall, RAF (1) 19 Driffield, Alamein Barracks (4) 53 Ternhill, Clive Barracks (1) 20 Feltwell, RAF (5) 54 Thorney Island, Baker Barracks (1) 21 Finningley, RAF (5) 55 Topcliffe, Army & RAF (5) 22 Gosport, HMS Sultan (1) 56 Turnhouse, RAF (1) 23 Hemswell (4) 57 Upavon, Army (2) 24 Honington, RAF (5) 58 Upwood, RAF (2) 25 Hullavington, Army (4) 59 Waddington, RAF (2) 26 Kemble, RAF (2) 60 Wattisham Airfield, Army (4) 27 Kinloss, RAF (3) 61 Watton, RAF (4) 28 Kirton Lindsey, Army (3) 62 West Raynham, RAF (4) 29 Leconfield, ASMT (5) 63 Wick, RAF (1) 30 Leeming, RAF (5) 64 Wittering, RAF (2) 31 Leuchars, RAF (4) 65 Wroughton, RAF (1) 32 Lindholme, RAF (1) 66 Wyton, RAF (4) 33 Linton-on-Ouse, RAF (5) 34 Little Rissington (4) (Total: approximately 196Type-C hangars remaining at 66 establishments) 4 December 2001

15 3 Description 3.1 IDENTIFICATION General Before commencing work on any hangar, it is clearly important to correctly identify the hangar type. The Type-C hangar is rarely confused with other types, exhibiting a typical multi-pitch roof with a series of ridges and valleys. The only other similar hangars are the Type-A and Type-B from which the Type-C design evolved, and few of these earlier types still remain. Virtually all Type C hangar roofs have the same steel structural frame, comprising a series of primary trusses at 7.62m centres (25ft) each with a clear span of 45.72m (150ft). The primary trusses, in turn, support secondary trusses at 4.572m centres (15ft). This structure forms the multi-pitched roof arrangement with a primary truss aligned on each ridge. At each end of the hangar there are six full height sliding doors, allowing both ends to be fully opened up Variations The Type-C hangar may vary in length, internal headroom and cladding material. The overall length is typically 91.44m and varies in 7.62m (25ft) increments from 45.72m to 91.44m (150ft to 300ft). The internal clear height for 1934 hangar of m (35'-4"), and for 1938 hangar of 9.246m (30'-4"), with an original roof covering either of asbestos cement slates or sheeting. The side walls are usually of brick or concrete although in the Cotswold area, they are sometimes in stone. The following table illustrates the main variations of Type-C hangars: December

16 Guide To World War II Hangars 3 Description YEAR SUB- GROUP 1934 (1) INTERNAL Width x Height 45.72m x m DIMENSIONS Length 91.44m WALLS Brick or stone DESCRIPTION Hipped end to each duo-pitch roof bay. Hangar 12 bays long and hangar gable ends align with a ridge. One patent glazed window to each bay, approx 6.2m wide x 4.4m high. Solid wall construction to top of wall at roof parapet level. (2) 45.72m x m 45.72m to 91.44m Brick or stone Hipped end to each duo-pitch roof bay. Hangar length determined by whole number of 7.62m bays. Hangar gable end align with a ridge, providing a vertical face of cladding above the doors. Windows and walls as before m x m 45.72m to 91.44m Concrete m x 9.246m 91.44m Concrete or brick Ditto Hipped end to each duo-pitch roof bay. Hangar 11 bays long plus 2no half bays at each end. Ends of hangar provide a pitched cantilever roof above the doors. Window height reduced to 3m but in panels either 13.4m or 21.4m long across 2 or 3 structural bays. Wall height only to top of windows, with asbestos cement cladding above to roof level. Figure 3.1 Main Variations of Type-C hangars. The previous table illustrates that there are two main variations of the Type-C hangar, the 1934 and the There is, in addition, a shorter span version, the structural details of which are not covered by this Guide. The photographs at figures 3.4 to 3.6 illustrate the typical external appearance of the Type C hangar, and show the differences between the 1934 and the 1938 versions. Figure 3.4 shows the rare situation of a 1934 and a 1938 version sited alongside each other. Figures 3.5 and 3.6 show enlarged views of these same hangars. Both have concrete walls, but each has been overclad during past refurbishment. The window areas have also been overclad in translucent sheeting of the same profile as the main wall cladding Annexes Most hangars were built with single storey annexes, often to both sides of the hangar and either in brick or concrete according to the hangar wall construction. These provided accommodation for offices, changing rooms, crew rooms, storage and workshops. 3.2 DRAWINGS Archive drawings A full list of microfilmed drawings and paper drawings is listed in Annex A, and are available from DE Information Management. These drawings have also been scanned, and are available in digital format (PDF documents) and are available from DE Information Management. Site specific as-built drawings are not kept at DE Information Management however, they may be available from the Property Manager or Project Sponsor for a particular site. In view of the reproduction quality of extant drawings, various new drawings were prepared for each of the 1934 and 1938 versions (sect 3.2.2). The following drawings were used in the structural appraisal and these drawings are available from DE Information Management if required. 6 December 2001

17 3 Description HANGAR DRAWING VERSION NUMBER /34 861/35 865/35 DRAWING TITLE General Arrangement: Plan sections of steelwork Roof Trusses Roof Trusses STORAGE MEDIUM Print Negative Negative Figure 3.2 Archive drawings used in structural appraisal New DE drawings The new drawings prepared by redrawing typical original plans and details are listed in the following table: HANGAR VERSION C type hangar (1934) C type hangar (1938) DRAWING NUMBER DE/H1/001/101 DE/H1/001/102 DE/H1/001/103 DE/H1/001/104 DE/H1/001/105 DE/H1/001/106 DE/H1/001/201 DE/H1/001/202 DE/H1/001/203 DE/H1/001/204 DE/H1/001/205 DE/H1/001/206 DRAWING TITLE General Arrangement showing original Drainage Foundation Plan and Details of Door Rail Foundations General Arrangement: Plan and Elevations General Arrangement showing Steelwork layout Line diagram showing layout and member sizes of Girder Truss A Secondary Truss sizes and layout of members General Arrangement showing original Drainage Foundation Plan and Details of Door Rail Foundations General Arrangement: Plan and Elevations General Arrangement showing Steelwork layout Line diagram showing layout and member sizes of Girder Truss A Secondary Truss sizes and layout of members Figure 3.3 Schedule of new DE drawings The above drawings have been prepared in AutoCAD and are held both on disc and as A1 size prints obtainable from DE Information Management. Copies of these drawings reduced to A3 size are included at Annex A Use of drawings Both the archive and newly prepared drawings should only be regarded as indicative of typical Type-C hangars. For any particular hangar, an on-site inspection should be undertaken to check the as-built structure and building fabric for comparison with the typical construction. The original as-built drawings for the site should be requested from the Property Manager. December

18 Guide To World War II Hangars 3 Description 8 December 2001

19 3 Description Figure 3.4 View of 1934 and 1938 Versions adjacent each other Figure 3.5 Typical 1934 Type C Hangar Figure 3.6 Typical 1938 Type C Hangar December

20 Guide To World War II Hangars 3 Description 10 December 2001

21 3 Description 3.3 MAIN STRUCTURAL ARRANGEMENTS Figure 3.1 indicated the main variations of Type C hangars. The following sections give further details of the typical main structural arrangements and member sizes. Reference should be made to relevant new drawings in Sect and to other archive drawings for further details. Providing the member sizes and arrangements are representative of those detailed on the drawings referred to at Section 3.2.2, the appraisal findings in the later sections are appropriate for use at option study stage Lattice roof girders The main girders span the full 45.72m span (150 feet) across the hangar between the columns at 7.62 m centres (25 feet) and support the secondary trusses. For both the Type C34 and Type C38 hangars there are typically three separate main girders referred to on original drawings as Girders A,D and E and their typical locations are shown in DE drawings DE/H/001/104 and 204. The three girder types are similar in size and layout, but by utilising different member sizes have different capacities. Figure 3.7 indicates the typical arrangement and member sizes for Girder A. Laced Column Laced Column E C F J C F K A G K A (plated) H K A (plated) H A (plated) H K K A (plated) H K A G K C F J C F E D D D B B B B D D D A 2 / 9" x 31/2" A 2 / 9 x 3½ x x lb/ft lb/ft BSC s BSC's B 2 / 9" x 31/2" B 2 / 9 x 3½ x x lb/ft lb/ft BSC s BSC's C C 2 / 29 / x 9" 3 x x 3" x lb/ft lb/ft BSC s BSC's D D 2 / 29 / x 9" 3 x 3" x x lb/ft lb/ft BSC s BSC's E E 2 / 15 2 / 15" x 6 x x 6" 45 x 45 lb/ft lb/ft BSB s BSB's F F 6 x 6" 5 x x 5" 25 x 25 lb/ft lb/ft BSB BSB G G 6 x 23½ / 6" x /2" x lb/ft BSC s lb/ft BSC's H H 6 x 6" 3 x x 3" x lb/ft lb/ft BSC BSC J J 2/6 2 x / 6" 3½ x x 31/2" x lb/ft lb/ft BSC s BSC's K K 2/6 2 x / 6" 3 x 3" x lb/ft lb/ft BSC s BSC's Figure 3.7 Main Truss Details Girders A December

22 Guide To World War II Hangars 3 Description Secondary trusses The secondary trusses span 7.62m (25 feet) between the supporting primary trusses. The truss depth varies along its span, having the depth of 4.9m at the supports and 1.23m at mid-span, thus forming valley gutters. The original roof was supported directly on the secondary trusses via timber sarking and purlins. Figure 3.8 illustrates the typical arrangement of a secondary truss with runway beam where fitted. Main Truss 7620 Main Truss A A M ain tru ss top chord B D A A D B C C E F C E C M ain tru ss bo tto m c ho rd 10" x 4 1 / 2 " or 10" x 6" Runway Beam A 2 / 4" x 2 1 / 2 " x 1 /4 " B 2 / 31 / 2 " x 3" x 1 /4 " C 2 / 4" x 3" x 5 /16 " D 3" x 3" x 1 / 4 " E 2 / 3" x 3" x 5 / 16 " F 2 / 2" x 2 1 / 2 " x 1 /4 " Figure 3.8 Secondary Truss Details New drawings DE/HI/001/106 and D/DE/HI/001/206 indicate the typical variations to secondary roof trusses. 12 December 2001

23 3 Description Columns and base A typical supporting column for a Type C hangar comprises two I beams tied together by a system of diagonal lacing angles, and encased in concrete over their full height. Fig 3.9 illustrates the concrete foundation detail. laced colum n. floor level Fig 3.9 Column Foundation Detail C34 columns are restrained at mid height by longitudinal 12 x 4 x 31 lb/ft and 9 x 3 x 17 lb/ft rolled steel channels which run along the length of the hangar. In each end bay of a Type C38 hangar a horizontal 6 x 3 rolled steel joist tie is provided Runway beams Two sizes of runway beams traverse the full width of the hangar. These run parallel to the main trusses and are attached to the underside of the secondary trusses at 4.572m centres. i.e. 2no. 10 x 4 1 / 2 x 25 lb/ft Joists with 1.5 Tonnes SWL 2no. 10 x 6 x 40 lb/ft Joists, with 6 Tonnes SWL Runway beams are not always present in hangars, neither are they present in each hangar bay Vertical bracing There are four sets of diagonal vertical bracing, two on each side of the hangar with each placed in the same structural bay as the roof wind girders at each end of the hangar. The drawings at sect indicate the roof wind girder and vertical bracing arrangements. December

24 Guide To World War II Hangars 3 Description Roof wind girders Two lateral wind girders span horizontally across the width of the hangar and are located in the last full structural bay at each end of the hangar Lattice stiffening girders (N Truss) At top of door level, these run longitudinally along both side elevations of the hangar Doors Each door measures approximately 10.7m high by 8 metres wide and weighs in the order of 12.5 Tonnes. They comprise a series of 10 x 3 channels and 10 x 4 1 / 2 RSJ s, which are externally sheeted in steel plate of varying thickness as follows: 1/4 plate up to 6m high and 1 / 8 " plate above. Originally, windows were fitted above 8.4m height, but these have frequently been replaced with steel plates. Internally the doors are sheeted in 1 / 2 " steel plate but only up to 6m height. Doors have sometimes been filled with gravel as blast protection. In the original design it is apparent that the steel sheeting on both the front and the rear faces on the door frames, are an integral part of the door structure. The steel plates provide strength and stability to the door frame members, and in the case of the lower diagonal bracing members, act as the gusset connection plates. 14 December 2001

25 4 Structural appraisal For the purpose of this Guide an initial structural appraisal was carried out for a typical Type C34 hangar using typical member sizes represented by the new drawings referred to in Section The purpose of the appraisal was to examine the main components of the hangar type to check the hangar s ability to carry the loading specified by current loading codes. Structural calculations were undertaken in support of the appraisal. The detailed findings of the appraisal are given later in the various sections which follow. These findings are given purely to assist in the preparation of option studies. The refurbishment solutions given in section 7 are appropriate for Option Study purposes providing that the site conditions, member sizes and loading circumstances are no less/worse than those considered in the appraisal. Where member sizes and loading circumstances differ it will be necessary to undertake further appraisal work at option study stage in order to check the applicability of the solutions offered in this Guide. In any event, the progression to Project stage will require provision of detailed surveys and calculations in support of the chosen option. It is recommended that where further appraisal work is undertaken the following publications are consulted. Appraisal of existing structures - 2nd edition, I Struct E Appraisal of existing iron and steel structures - SCI publication 138 Assessing the capacity of existing steelwork - SCI paper AD135 Historical structural steelwork handbook - BCSA The remainder of this Chapter concentrates on the assumptions made in the appraisal process and the detailed findings. An indication is given of the process that a professional civil/structural engineer will normally take prior to advising on the structural adequacy of a site specific Type C hangar and its proposed refurbishment. 4.1 DESIGN PHILOSOPHY The calculations in support of the appraisal were carried out in accordance with the following standards: BS Use of Structural Steelwork in Buildings BS Use of Structural Steelwork in Buildings BS Part 1 Loading for Buildings Code of Practice for dead and imposed loads BS Part 3 Loading for Buildings Code of Practice for imposed roof loads BS CP3 Chapter V Part Code of Basic data for the design of buildings - wind loads TICE 104 No 1986 Appraisal of existing and design of new runway and lifting beams (then extant) The appraisal calculations were undertaken to check the main structural members so that informed professional judgement could be made of the adequacy of the generic Type C hangar. December

26 Guide To World War II Hangars 4 Structural appraisal The assumptions made in the appraisal of this generic Type C hangar may, due to site circumstances, not translate to other Type C hangars. The loading conditions, predicted future use, projected life span etc., will vary from site to site. It is recommended that, at Option Study stage, suitable allowances are made for deviations from assumptions made in the appraisal used for this Guide and that a site specific analysis is always considered before drawing any firm conclusions. There are two extant British Standards which could be used in the design of steel frame buildings; namely BS5950 and BS449. Great debate exists as to which of these two codes is more appropriate for the analysis of historical structures. Final selection is to be based upon professional judgement dependent upon the particular circumstances of the structure and scale of project in question. Because this Guide is primarily to support the Option Study process it was considered that use of BS CP3 and BS 449 was appropriate. For new Projects and for the refurbishment of Type C hangars the use of BS 6399 and BS 5950 is considered to be appropriate. 4.2 MEMBERS ANALYSED For the Type C34 hangar the following structural members were analysed: Typical main girders type A, secondary trusses, columns, column foundations runway beams, vertical bracing and roof wind girders. Amongst others, the following members were not checked: Longitudinal edge beam, walls, parapets, purlins, doors, door supports and gantries; untypical members such as end trusses, C-38 cantilever trusses, C-38 main truss supporting cantilever trusses, columns supporting end main trusses, C-38 columns supporting cantilevered roof and associated untypical foundations. The analysis for individual elements of the structure are described in Section 4.4. The most heavily loaded portal frame was considered to be the central frame which supports two 6 ton runway beams. The beams span between the secondary trusses, one beam each side of portal frame (see drawing DE/H1/001/104). 16 December 2001

27 4 Structural appraisal One typical frame was therefore checked as part of the appraisal consisting of: Secondary trusses - span simply supported between main truss portals. Main portal frame and - two cases were checked a) pinned feet portal; stanchions b) fixed feet portal. Foundations - sizes on original drawings were based on a 2 ton per sq ft permissible ground bearing. it was assumed as part of the appraisal that bases have been increased/decreased pro-rata to suit existing ground conditions. Vertical & Horizontal - this was checked on assumption that bracing Bracing one end only is taking full load. 4.3 BACKGROUND TO PERMISSIBLE STRESSES AND LOADING USED IN THE APPRAISAL The hangars were assumed to have been designed in accordance with the current standards of the day. BS449 (1932), BS449 (1937) and BS15 (1930). These stated permissible working tensile stress of 8 tons/sq in (124N/mm 2 ) and an ultimate tensile strength of tons/sq in ( N/mm 2 ). The quality of steel has obviously improved since those dates, therefore, the appraiser considered it prudent to check the structure on the original permissible stresses rather than compare with todays permissible stresses. The appraiser discussed with British Steel the method of design most appropriate to steel of this age. It was suggested that limit state design was not applicable and, therefore, the steelwork was checked against the permissible working stresses of BS Invaluable data on steelwork properties is summarised in the BCSA publication Historical Structural Steelwork Handbook. Further guidance with particular emphasis on steel quality is given in the Steelwork Construction Institute paper AD135 - Assessing the capacity of existing steelwork. Since 1932, wind load requirements together with applied live loads have been significantly increased. In BS449 (1932) the wind force requirement was a standard 15lb/sq ft (0.72KN/mm 2 ) on vertical surfaces. The superimposed loading on roofs which are inclined at more than 20 0 to the horizontal was 15lb/sq ft inwards on windward slopes and 10lb/sq ft (0.48KN/m 2 ) outwards on leeward slopes. These loads were deemed to include wind and were assumed acting normal to the surface. Superimposed loading on a flat roof was to be designed for 30lb/sq ft (1.44KN/m 2 ). The interpretation of the appraiser was that the hangar roofs were never designed originally to support any snow loading, only a wind force of 15lb/sq ft (0.72KN/m 2 ) maximum normal to the roof surface. Today, that same roof structure must not only be capable of sustaining a uniform snow load but also be able to withstand local drifting of snow in the valleys although with the drifting situation the current BS6399 does allow a reduced factor of safety. At the time of appraisal wind forces for the hangars were calculated in accordance with CP3. The appraisal calculations were originally prepared using the most onerous location for a hangar ie. Scotland. The findings indicated that the hangars were grossly overstressed. It was then considered that the loadings for Scotland were not really compatible with the location of the majority of hangars. The structure was, December

28 Guide To World War II Hangars 4 Structural appraisal therefore, rechecked with loadings of a lesser magnitude taken for an area based in South Yorkshire/Lincolnshire where a large number of hangars exist. A basic wind speed of 45m/s was, therefore, used in the calculation. A copy of the basic wind speed map taken from Fig 1. of CP3: Ch V: 1972 is attached in Annex D. Subsequent to the appraisal, BS6399 Part 2 has been issued and for Option Study purposes only it is considered that loadings are unlikely to be significantly increased. The initial intention had been to report on the general adequacy of the hangar rather than undertake a fully detailed structural analysis. However, due to the complexity of the various possible loading conditions the appraisal included a fairly rigorous analysis. A single set of 1934 hangar truss detail drawings was used checking the design i.e. drg 861/35 and 865/35 as detailed in fig 3.2. The section sizes were reproduced onto line details i.e. Drg No DE/H1/001/105 and Drg No DE/H1/001/106 refer. The design check was carried out to these sizes. The findings are representative of roof trusses made up of those members only. A compromise between a fully detailed analysis and a cursory check was, therefore, undertaken. Forces and stresses in a typical 1934 hangar main frame and a single secondary truss were calculated based on two dimensional analysis only. Checks were carried out on the riveted/bolted connection based on drawing No 865/35. The structural members were checked and the working stresses compared with the basic permissible stresses specified in BS BS , like the current BS449, allowed the permissible working stresses to be increased to allow for wind loading. The judgement was that there were reasonable factors by which the basic permissible working stress could be increased when the structure is designed for wind loading conditions Wind loading The appraisal check was in accordance with CP3:Ch V: Snow and imposed roof loadings Snow loading was applied in accordance with BS6399 : Part 3 : Basic snow load, s b = 0.6 kn/m 2 Assumed site altitude : less than 100m Runway beams The two different types of runway beam were individually checked for their respective capability to support 1.5 tonnes or 6 tonnes. In addition, for the general design check of typical secondary trusses, a runway beam loading of 6 tonnes was applied. In the case of the main trusses, it was assumed that this 6 tonnes load could be applied simultaneously to both sides of the truss. 18 December 2001

29 4 Structural appraisal Dead and services loading A loading of 0.44 kn/m 2 on plan was applied to allow for roofing materials and nominal building services. 4.4 OUTCOME The appraisal found that for the locations considered in the study the Type C type structure is capable of carrying loadings specified by loading codes at time of appraisal. This is without excessive cracking or movement provided that the structure was constructed as originally designed and had been maintained to a reasonable standard. This view was given based on a set of calculations for: Runway Beams Snow Loading Wind Loading Dead Loading Secondary Truss Main Frame Wind Girder Vertical Bracing Column Foundations and was based on: Existing Air Ministry Drawings 2029/34 - GA Steelwork 861/35 - Secondary Truss with 6 T runway beam 865/35 - Main Roof Girder Type A The following loading cases were considered for the secondary and main roof trusses. Load Case B1. Load Case B2. Load Case B3. Load Case B4. Load Case B5. Load Case B6 Load Case B7. Load Case B8. Runway Beams Loaded each side of truss Runway Beam Loaded at one side of truss Local Snow Drifting in Valley Uniformly Distributed Snow Load Net upward wind force Net Downward wind force Dead Weight from Secondary Trusses Structural Self Weight The member dimensions used in the appraisal have been included on the new DE drawings. (Sect 3.2.2). The findings of the appraisal do not extend outside the defined geographical area referred to earlier, or outside the assumptions made in the appraisal Secondary roof trusses These trusses form the valley gutters and span between the main trusses. The trusses also support the lifting beams which traverse the width of the hangar. December

30 Guide To World War II Hangars 4 Structural appraisal Appraisal calculations indicated that under all loading conditions above, the structural members of this truss are acting within the permissible increased working stresses. This is based on the structural sections shown on the Drg DE/H1/001/106 reproduced from original Air Ministry Drg No 861/35, which is for the truss providing support for the heaviest lifting beam (i.e. 6 ton capacity). Some members on other unchecked trusses are of smaller section but support lifting beams of 1.5 ton capacity Main roof trusses These trusses span the full width of the hangar, acting as a portal frame with the perimeter columns. The trusses support the secondary trusses spanning in between. The appraisal found that: 1) Bottom Boom Member - satisfactory under all conditions. 2) Internal Vertical Members - satisfactory under all conditions. 3) Internal Diagonal Members - satisfactory under all conditions. 4) Top Boom Member - does not exceed the limit of increased permissible working stress under the load cases defined in clause ) Main truss connections - Structural connections were considered from the original Air Ministry drawing No 865/35. It was judged that for the purpose of the study there were reasonable factors by which the stresses could be increased when the structure experienced wind loading. It was concluded that site based information should be used to confirm the adequacy of connections Runway beams 2 No 10 x 4½ x 25 lb/ft RSJ runway beams traverse the width of the hangar. They span between the secondary trusses and are required to support a SWL of 1 1 / 2 tons. Similarly 2 No 10 x 6 x 40 lb/ft RSJ with an additional top flange plate provides for runway beams capable of supporting a SWL of 6 tons. Both sizes of beams were considered to be capable of sustaining their applied loadings subject to the adequacy of the connections Roof wind girder 2 No wind girders span the width of the hangar and are located one at each end. These were found to be adequate to resist the wind forces calculated to CP3:ChV:1972. The members normal to the top and bottom booms were checked on the assumption that they are providing an intermediate vertical support for the self weight of the diagonal members. This additional loading was still within the allowed increase to permissible working stress. 20 December 2001

31 4 Structural appraisal The total wind load on the end of the hangar was assumed to be taken by a single wind girder. The wind girder at the opposite end was ignored Vertical bracing There are 4 No sets of diagonal vertical bracing, 2 sets per side of hangar. A pair of wind braces at one end of the hangar were found to be adequate to safely transmit the total wind forces to the ground Steel stanchions These consist of 2 No 15 x6 x45 lb/ft Universal Beams, diagonally laced together and encased in concrete. The columns have been analysed as pinned and then as fully fixed at their base to establish the two boundary conditions and, mindful of the extent to which they are encased in concrete, the stresses were considered satisfactory under the encased condition Foundations The information available was a standard drawing based on a permissible ground bearing pressure of 2 tons/square foot now reproduced at Drg DE/H1/01/102. A note on the original drawing stated that the bases should be designed to accommodate the permissible ground bearing at the individual location. Calculations were carried out on the foundations sizes based on the 2 tons/square foot permissible bearing pressure. The bases were adequate for vertical loading, but once bending moments were introduced, the ground was theoretically overstressed. No information on actual base sizes was available for specific locations. It was noted that there had been no reports of foundation failure. It was reasoned that since the hangars had presumably been exposed to extremes of loading at some time during their sixty years of life, and that no adverse effects had been recorded, then engineering judgement must be that the foundations have proved capable of sustaining the actual forces applied. It was recorded that holding down bolts were acceptable, and capable of taking the wind forces. 4.5 CONCLUSION Based on the findings of the appraisal, DE's conclusions are 1) that structural capability of the hangars to carry current day loading (ie. CP3 at the time of appraisal) can be considered adequate for the locations covered. Outside the 45 m/sec basic wind speed contour eg. Yorkshire, Cornwall, Wales, the wind and snow loadings increase and where an overstress could be considered acceptable elsewhere it is unlikely that the other hangars (especially in Scotland) can be justified. However, it is reasoned that since all calculations in the above appraisal had been based on a very restricted number of detail drawings it is likely that the other hangars have been designed for the more onerous local conditions. 2) the Northern hangars are still standing after 60 years and this is an indicator for use in professional appraisals. December

32 Guide To World War II Hangars 4 Structural appraisal 3) the trusses have proved the test of time of 60 years and provided the members are adequately maintained and repaired, the trusses should continue to provide a structurally sound roof support. 4) the stanchions appeared to be approaching maximum increased permissible working stress. It, therefore, seems reasonable to accept that the stanchions will continue to provide adequate support even with the loading requirements extant at the time of appraisal. 5) there did not appear to be any record of severe settlement occurring to the hangars, especially to the hangars in the area previously covered by what was once the PSA North East region on whose records the appraiser's report has been based. It was not possible to confirm that the foundations are adequate. One original standard foundation drawing was found but this was based on a 2 tons/square foot bearing capacity with the proviso that all locations should have their foundation redesigned to suit the relevant conditions. Calculations showed that these bases could be overstressing the ground during exceptional loading conditions at short duration. 6) in summary, it is proposed that for option study purposes the Type C hangars are structurally sound, and capable of sustaining current loading conditions. This view relates to the main structural members and the information is based upon a single set of standard drawings with the assumption that all hangars considered had been constructed to equivalent details, or to enhanced requirements commensurate with the loading at their location. 7) individual Option Studies for specific locations will require an appraisal of the basic structure to confirm it is adequate for the actual loadings. 4.6 IMPLICATIONS OF APPRAISAL CONCLUSION It is, therefore, considered that the findings are appropriate for use at Option Study Stage. The preparer of a future Option Study should make suitable adjustments to cover: a. actual geographical location b. actual type of hangar c. actual knowledge of member sizes d. changes to loading e. changes to wind codes issued subsequent to the appraisal f. changed understanding of how pre-war steelwork performs g. removal of wind speed limitations covered by TB 99/29 h. changes to suit temporary condition of loadings 22 December 2001

33 5 Operational requirements 5.1 INTRODUCTION Like the majority of hangars on the MOD estate, the Type C hangar is currently subject to various operational requirements, in relation to concern about structural safety for heavy snowfall and high wind situations. 5.2 HANGAR BUILDING The general structural appraisal identified that there are circumstances when the structure of a Type C hangar may have the normal structural safety factors reduced to levels of concern eg. during complete door removal or introduction of dominant openings in the end quarter of the gable elevations. The onus is, therefore, on the EWC undertaking technical inspections and professional appraisals to identify site specific matters which may require further consideration. The appraisal was undertaken using a basic 3 second gust wind speed of 45m/sec as taken from and applied in accordance with CP3 For locations with a basic wind speed above 45m/sec eg., Scotland, Cornwall, Wales, Northern Ireland, and Yorkshire, the PROM will need to ensure that the EWC advises on the implications as part of the professional appraisal under DE Spec 005. The EWC will, therefore, need to produce site specific guidance on the permissible loading arrangements taking account usage of runway beams, heavy snow, high wind gust speeds, and the actual member sizes at the site concerned. It is not possible in this document to give specific recommendations for each Type C. This is because there are site specific matters to take into account. eg. condition of structure building orientation altitude weight of building services In order to minimise further risk of overstress, the generic guidance is: a) the load-carrying capacity of any runway or other lifting beam should be certified and clearly marked on the beam (already an extant requirement) b) the adequacy of the supporting structure needs verifying as part of the professional appraisal c) for hangars covered within the 45m/s wind speed contour the findings of this Guide may be used to supplement site based conclusion December

34 Guide To World War II Hangars 5 Operational requirements d) keep hangar doors closed when winds are gusting at speeds of 27m/s and greater, in accordance with Technical Bulletin 99/29 e) Keep hangar doors closed when high winds and heavy snow are forecast and do not use the runway beams Users are advised to undertake Risk Assessments, to recognise both the financial and strategic value of equipment stored in hangars, and to appraise the significance and implications of any potential loss. It may be necessary to devise an Emergency Action Plan to protect valuable or important equipment from loss or damage. 5.3 PROFESSIONAL AND TECHNICAL INSPECTION The current property management arrangements for hangars are contained in DE Specification 005. The EWC duties are: Technical Inspection (Task 584) 2 yearly Professional Appraisal (Task 582) 5 yearly It is recommended that the Technical Inspections have specific regard to the matters raised in the documents and in particular the corrosion of structural frame eg. outriggers, corrosion of guttering, etc. It is required that the outcome of the Technical Inspection is subject to review by a Chartered Civil/Structural Engineer. It is required that the Professional Appraisal is undertaken by a Chartered Civil/ Structural Engineer and that the continued ability of the structure to perform its function for the next 5 years be confirmed. Where the EWC identifies areas of concern through either the Technical Inspections, the Professional Appraisals or reports from others, the operational implications are to be considered by the Property Manager. In the event of concern the precautionary measures should follow the typical scenarios established by the TB 99/29 see Annex E eg. site specific measures to be taken during snowfall, before and during high winds. Emergency action plans are required to cover these and other situations. 24 December 2001

35 6 Refurbishment - General 6.1 INTRODUCTION Refurbishment is normally the most economical and practical solution for a Type C hangar, rather than demolition and new build. The main elements of work to be considered are roofing and gutters, vertical cladding (1938 version only), windows, walls and doors. It may also be necessary to repair or renew the ground floor slab to suit loading requirements. Although the mechanical and electrical services usually also require repairs or renewal, this is outside the scope of the Guide, however, such work should be considered at the same time as the main building work. The full life cycle implications on maintenance, operation and efficiency are to be taken into account. Each refurbishment option is to consider heating losses and ventilation requirements. 6.2 OPTIONS AND RECOMMENDATIONS For any refurbishment project, an Option Study needs to be carried out in order to establish the most cost effective solution. Reference should be made to BS 7543 : Guide to Durability of Buildings In carrying out such a study, the generic information contained within this Guide is to be quoted with any departures highlighted. This base information can include the form of construction, as shown on the drawings in Annex A (a). The Budget cost estimates for Option Study purposes for the various roof options are given in Annex I. These can be quoted and updated to suit current requirements. The choice of roof configurations and roofing material is usually a major constituent of any refurbishment project, and accounts for the largest expenditure item. Every Option Study is to include the 'Flat Roof' Option. A review of recent option studies for a number of sites, where different methods have been used, the recommendations for the main roof element is to provide a 'Flat Roof' system, incorporating either a single ply membrane or the aluminium standing seam system, depending upon the life span required. Further details of the separate refurbishment options for all of the elements are detailed in the chapters dedicated as follows: Roofing (Chapter 7) Gutters and Drainage (Chapter 8) Windows (Chapter 9) Walls (Chapter 10) Doors (Chapter 11) Each element of work will be considered separately and where necessary detailed guidance will be covered in a relevant Annex. December

36 Guide To World War II Hangars 6 Refurbishment - General 6.3 WARRANTIES/GUARANTEES The installation of manufactured products can often be accompanied by a warranty or guarantee. An examination is required of the associated terms and conditions to establish the extent of any caveats. A check should also be carried out on any existing warranties that may still be in force from any previous works. If such warranties do exist, then continued applicability needs to be confirmed. A further indication as to the credibility of an installed system can be demonstrated through accreditation by an independent testing house such as the British Board of Agrément. Careful consideration should be given to any conditions which tie MOD to continued involvement with the installing or supplying company. Such conditions may act to the long term financial detriment of MOD and may adversely affect the ability of the EWC/WSM to effectively undertake their duties. Where a guarantee is regarded as appropriate, it should be fully underwritten and insurance-backed. For building systems comprising a number of products such as roofs or windows, guarantees should cover a whole system as installed including all fixings, sealants, glues, jointing systems, cut edges or any other treatment to the materials necessary for installation. It is also essential to consider the extent, frequency and cost of any inspections or maintenance necessary to ensure continued validity of the guarantee. A quality installation is one which incorporates good design and skilled workmanship. It is, therefore, important that full attention is given at the outset. The guarantee/warranty is normally a confirmation of that process. In the event of a failure it is very unlikely that the guarantee/warranty will cover other than the building work. The costs of disruption will normally still fall to the user. 26 December 2001

37 7 Refurbishment - Roofing 7.1 DESCRIPTION Original Type C hangars have multi-pitched roofs separated by valley gutters at 7.62m (25ft) centres. With the exception of the earliest 1934 Type-C hangars, the end of each duo-pitch roof is hipped and rainwater run-off is collected by edge gutters behind parapet walls along each side of the hangar. Each internal valley gutter links with the edge gutter. In the earlier 1934 variations, the end of each duopitch roof is gabled without the edge gutter and all rainwater is collected by the valley gutters which are not linked. 7.2 PROBLEMS a) The roof arrangement of a typical 300ft x 150ft 1934 hangar involves some 2200ft (670m) of gutters, comprising 1650ft (503m) of valley gutters and 550ft (167m) of perimeter wall gutters. The entire system has no overflow capability, resulting in blockages causing unacceptable discharge into the hangar building. Maintenance of the roof and gutters is of crucial importance if overflow problems are to be avoided. b) The internal cast iron rainwater down-pipes and underground drainage require maintenance if internal flooding due to pipe blockage and joint leakage is to be avoided. c) The multi-pitch configuration produces potentially high snow loads when drifting arises in the valleys. d) The multi-pitch roof configuration includes a large number of hip and ridge tile runs, as well as numerous awkward flashing arrangements. These are areas of frequent maintenance and also add to the cost of re-roofing works. e) The original 1930's roof construction comprises asbestos cement tiles or corrugated sheeting fixed to timber battens on close boarding and supported by timber purlins spanning onto the secondary trusses. After some 60 years, the finishes are normally in need of replacement. f) There is a significant amount of heat loss through the original multi-pitch roof, arising from: 1) ventilation via the valley gutters 2) lack of insulation, and 3) large surface area of roof because of the multi-pitch arrangement. December

38 Guide To World War II Hangars 7 Refurbishment - Roofing 7.3 ROOFING REQUIREMENTS Other than the obvious requirement for a roof to resist water leakage, the following general requirements apply: Fire rating The roof construction shall comply with Crown Fire Standard E10. In summary, the materials must be self-extinguishing and must resist penetration by fire or hot airborne debris either from within or outside the hangar. This has two objectives: any fire within the hangar is contained and does not spread to other adjacent buildings fire occurring outside the hangar cannot penetrate the roof and spread to areas within the hangar which may be protecting valuable equipment Existing Type C hangars have dispensation regarding requirement for internal spread of flame (Sect 19 of Technical Bulletin 99/31). Colour For hangars, the roof colour is rarely of aesthetic importance. However, in the vicinity of airfields, very light colours can create a dazzling hazard being highly reflective of sunlight. Conversely, dark colours absorb more heat which hinders the control of internal temperatures within the building and the greater range of temperatures increase thermal stress on materials. A medium but dull shade is preferred, but as light as is acceptable to flying operations. The Sponsor should confirm the requirement. Durability The proposed lifespan should meet the needs of the user. As discussed under "Warranties" in section 6.3, care must be taken to ensure that all components of a roof system have the same required lifespan including all fixings, sealants, glues, jointing systems, cut edges or any other treatment occurring during installation. Independent accreditation The roof system should have accreditation by an independent testing house, such as the British Board of Agrément or other European equivalent. Thermal insulation The minimum requirement is to raise that element being refurbished up to the current standards. Investment appraisal techniques can be used to indicate that, to spend to save is justified by increasing the thermal efficiency of the roof and other elements. Lightning protection Lightning protection needs to be considered as part of the refurbishment. There is a requirement to carry out a risk assessment for the structure to determine whether the structure needs protection. BS 6651 : 1999, provides a mathematical risk analysis method, which considers, the geographical location, effective collection area, use of the structure, type of construction, contents, location and topography. 28 December 2001

39 7 Refurbishment - Roofing Non-metallic roofing systems normally require a network of air terminations, which link into the existing structure, and require down conductors to achieve earthing. Metallic roofing systems do not normally require the networks of air terminations, but links to the existing structure, down conductors and earthing are required. Careful design and attention to detail is vital to the successful installation of the protection system. 7.4 ROOFING MATERIAL Materials There are several roofing materials/types which may be considered: A) single ply membrane, for which there are various different materials B) standing seam concealed-fix aluminium sheeting C) traditional profiled steel sheeting D) traditional profiled aluminium sheeting E) composite sheeting F) fibre cement sheeting G) existing asbestos cement sheeting retained, repaired and coated with waterproof compound. Annex F provides further information on these and includes comprehensive references. A) to D) are used as part of built-up roofing systems comprising a series of separate layers, including liner sheets, vapour control membranes and insulation, all assembled on site. E) comprises manufactured panels of sandwich construction effectively preassembling the liner sheets, insulation and external sheeting together off site. F) and G) involve labour intensive work on site. Neither lend themselves to providing additional insulation, unless placed to the underside of the roof within the hangar (not always a practical solution) and not preferred due to possible condensation problems. The above materials have different degrees of flexibility for how they may be used in roofing solutions. December

40 Guide To World War II Hangars 7 Refurbishment - Roofing 7.5 ROOFING OPTIONS There are many different materials which may be utilised to refurbish a Type C roof. When these are combined with the different possible roof layouts and roofing techniques the options and sub-options for roof refurbishment are limitless. Any major roof refurbishments should replace all existing fragile roofing materials. Over the years, many different methods have already been utilised on MOD's hangars and an examination of these together with a detailed study of particular solutions have identified that four options are considered. Option R1 Flat Roof is the DE recommended solution. The latter one R4 represents poor value for money Option R1 - Flat Roof (DE Recommended Solution) R1a - Flat roof single ply membrane R1b - Flat roof aluminium standing seam Option R2 - Multi Pitch Roof R2a - Multi pitch roof built-up steel cladding R2b - Multi pitch roof built-up aluminium cladding R2c - Multi pitch roof composite steel cladding Option R3 - Multi Pitch Retain Patch and Repair Option R4 - Repair and coat original sheeting with a waterproof compound At major refurbishment, the DE recommended solution is a Flat Roof utilising either Option R1a single ply membrane or Option R1b aluminium standing seam, depending upon the projected life requirement for the hangar and a detailed investment appraisal to suit the specific requirements of the hangar. Problems with 'flat' roof options at particular coastal sites have been reported to DE. These relate to the likelihood of birds being attracted to 'flat' roofs for nesting or roosting. Therefore, the advice is to consider any existing local problems, and the likelihood of this been increased due to any refurbishment project. Particular advice should be sought from the relevant authorities at option study stage, such as the Birdstrike Avoidance Team. The retention of the multi pitch roof has many technical and financial disadvantages, but may in certain circumstances be retained to meet a site specific requirement to retain external appearance. Where Option R2 is specified the PROM should ensure that all the implications of retaining the multi pitch roof are fully understood and included within the full life costings. Option R3 should only be considered as a short term low reliability solution and is not recommended. Option R4 is not recommended and represents poor value for money. Annex F contains details of many of the different roofing systems examined, but the remainder of this Chapter is dedicated to the above options. At major refurbishment, the DE recommended solution is, therefore, Option R1. Provide new Flat over-roof. ie. this has the advantages detailed under 7.6. Should individual sites have a long term specific wish to retain the multi-pitch configuration ie. Options R2 and R3, the Guide indicates other matters for full consideration. 30 December 2001

41 7 Refurbishment - Roofing 7.6 DETAILED DESCRIPTION OF ROOFING OPTIONS The options are now described in detail together with drawings for illustrative purposes only Option R1: Flat over-roof The shallow fall provided by this solution requires that the roof is finished either in material A (single ply membrane) or B (standing seam conceal-fix aluminium sheeting). For this concept all of the existing cladding, boarding and timber purlins are removed, (providing the stability of the secondary truss members are not affected), but the steel structure is retained. The new roof is formed by spanning steel beams laid to a fall, and supported off steel stubs at the main truss node points, (some of the steel stubs may require stability bracing). Cold rolled purlins at centres to suit proposed cladding. These span across the 7.62m centres of the trusses, carrying a pitched roof typically to a fall of 1 in 40 (2.5%). This fall raises the roof by about 600mm above the existing along the centre of the hangar. The roof liner sheeting should be galvanised for durability or may be in aluminium for material B. A brighter internal working environment can also be provided if the liner sheeting is colour coated in a reflective light colour such as white. December

42 03 - Type C hangar 7 Refurbishment - Roofing Laced Column Purlins on stub columns F Figure 7.2 Option R1 Secondary New truss flat roof details profile igure 7.1 Option R1 Main truss details Gutter Laced Column Main roof girder truss Lattice stiffening girder Figure 7.1 Option R1 Main truss details 32 December 2001

43 7 Refurbishment - Roofing Flat roof over comprising either single ply membrane or aluminium standing seam sheeting with insulation on vapour control layer and profiled lining panels. Cold rolled purlin Stub column. Secondary truss spanning 7.62m between main trusses. Figure 7.2 Option R1 Secondary truss details The advantages of roof option R1 are as follows: a) all valley gutters are removed which removes the cost of valley gutter renewal both initially and in the future; (gutter replacement intervals often differ from those for roofs) removes a major ongoing maintenance liability removes the possibility of valley snow loading occurring removes a source of likely leakages arising from overflow due to blockages removes the air loss via the valley gutters - a main source of heat loss b) compared to the multi-pitch arrangement, the flat roof concept reduces the overall surface area of roof, thereby: reducing the cost of the roof, due to use of less materials reducing heat losses, due to reduced roof area c) with both the membrane and standing seam solutions, no fixings or sealants are exposed to the external hostile environment, thereby: minimising the maintenance requirement minimising the risk of roof component failure December

44 7 Refurbishment - Roofing The disadvantages of option R1 are as follows: a) the need for some additional supporting structural steelwork, and for deeper purlins to span between the main trusses b) due to removal of purlins on the secondary trusses the stability of the members under compression will need to be checked as part of the design process and additional provision made for lateral stability c) marginally longer construction period than option 2 d) the ability of the roof drainage systems to hold water is reduced thus leading to quicker run off with possible flooding consequences e) it will require total possession of the hangar Option R2: Multi-pitch profile, removing existing timber boards This option retains the existing multi-pitched roof profile, and reclads the roof in built up steel or composite cladding. It assumes that the condition of the existing timber boarding and purlins necessitates their removal. New purlins are provided spanning about 7.62 m between the secondary trusses. These support new liner sheets, insulation and new roof covering as per the desired material option. The liner sheeting should be galvanised for durability unless in aluminium. A brighter working environment can also be provided if the liner sheeting is colour coated in a reflective light colour such as white. If the gutters are more than five years old it would normally be cost effective to also renew all valley and perimeter gutters at the same time to aim for compatible life spans. Renewal periods for gutters and roof materials often differ, and access for future gutter work can be limited if the roof is to remain undamaged. The advantages of roof option R2 are as follows: a) the external appearance of the building remains largely unchanged b) materials A and D may be used, offering a similar lifespan to roof option R1 Disadvantages of roof option R2 are: a) the valley gutters remain, with consequences to renewal and maintenance costs, disruption at future gutter renewal, risks of leakage, and valley snow loading. Heat losses are not reduced b) the multi-pitch arrangement requires: greater cutting of roof sheeting, thus increasing labour and material wastage costs greater detailing arrangements for ridge, hip and flashing 34 December 2001

45 7 Refurbishment - Roofing Roofing Option R3: Multi-pitch profile, retaining existing timber boarding This option is very similar to roof option R2, except that the existing timber boarding and purlins remain. There may be a need for some local repair and partial renewal of deteriorating timber. All timber, new and retained, should be fully treated with a solvent based preservative for rot and insect attack. To support the new overlying sheeting, new metalized purlins will be placed on the boarding with fixings through into the timber purlins beneath. The depth of the new metal purlins is usually determined by the insulation thickness and ventilation gap, rather than a spanning requirement. Insulation is supported directly by the retained timber boarding, in lieu of providing new liner trays. It is preferable to review all valley and perimeter gutters at the same time as major roofing works, thus aiming for compatible lifespans. Future gutter replacement can be very difficult, is disruptive for the occupants below and can cause damage to the roof. New cold rolled purlins bolted through boarding into existing timber purlins. Profiled metal roof sheeting with insulation on vapour control layer. Existing boarding retained as liner to be repaired and preservative treated. Secondary truss spanning 7.62m between main trusses. Figure 7.3 Option R3 Secondary truss details The advantages of roof option R3 are the same as for option R2 with the addition of the following: a) a cost saving is made by retaining the existing timbers b) the construction period is marginally shorter than for other options c) by retaining the inner boarding, there is less disruption to the occupancy of the hangar during refurbishment. December

46 7 Refurbishment - Roofing Disadvantages of roof option R3 are the same as for option R2 but the following additional matters must be considered: a) the lifespan of the roof is dependent on the adjudged longevity of the retained timbers b) the need for additional timber repairs may be uncovered during the refurbishment work, resulting in extra costs, possible delays and potential contractors' claims Roofing option R4: Repair and coat original sheeting with a waterproof compound Where a defective roof needs making good for a short term, eg. less than five years, a proprietary overlay or patch repair system may be considered. If the gutters are in a poor condition, their repair should be considered prior to the application of compound, because subsequent repair would be very disruptive and potentially damaging to the existing roof. Wholesale gutter replacement and renewal is not advocated for this short term solution. Existing sheeting retained, to be cleaned, repaired and coated with a proprietary waterproof compound. Existing baording and timber purlins retained. Secondary truss spanning 7.62m between main trusses. Figure 7.4 Option R4 Secondary truss details The advantages of roof option R4 are as follows: a) the construction period is shorter than that for Option R1 b) there is limited disruption to the occupancy of the hangar during the work. 36 December 2001

47 7 Refurbishment - Roofing The disadvantages of roof option R4 are: a) it is very expensive compared to the other options b) the lifespan of the roof is short and is dependent on the old timbers and condition of asbestos cement. It should not be regarded as a permanent solution. It gives very poor value for money c) unless insulation is provided in some other way, this roof construction will lose heat quicker than through the other options d) being covered by the asbestos sheeting, the underlying timbers will be difficult to effectively treat with a suitable preservative e) the need for additional timber or sheeting repairs may be uncovered during the work, resulting in extra costs, possible delays and potential contractors' claims Matters to be considered with all options efficiency in use especially long term maintenance, heating costs, etc. roof access lightning protection disruption during works. 7.7 SUMMARY OF ROOFING OPTIONS OPTION R1 Provide new flat over-roof: using either a single ply membrane or standing-seam aluminium sheeting, including new purlins and insulation. OPTION R1 IS THE RECOMMENDED OPTION. OPTION R2 OPTION R3 OPTION R4 Retain existing multi-pitch roof profile: Remove existing timber boarding, and reclad with new profiled metal sheeting, purlins and insulation. Retain existing multi-pitch roof profile: As Option R2, but retain and repair existing timber boarding. Retain existing multi-pitch roof profile: Clean, repair and coat existing sheeting with a waterproof compound. A tabulation of these options is given at Annex F. December

48 7 Refurbishment - Roofing 38 December 2001

49 8 Refurbishment - Gutters and drainage 8.1 DESCRIPTION Gutters constitute a major weakness with the traditional multi pitch Type C roof. At major refurbishment, every effort needs to be taken to ensure that this, often overlooked and trivialised area, is properly addressed and an adequate solution fully developed and specified. The original gutters were typically 455mm wide by 155mm deep, and constructed in 5mm thick galvanised mild steel. Subsequent maintenance may have involved the painting or covering in bitumen sheeting or other waterproofing material. There is a parapet gutter 84m long to each side of the hangar, and a series of valley gutters each 46m long within the multi-pitch arrangement. The 1934 version has 12 valley gutters (552m total length), and the 1938 version has 11 valley gutters (506m total length) but with eaves gutters, each 46m long above each end door. The valley gutters discharge into the parapet gutters, which, in turn, discharge into a series of 152mm diameter cast iron down-pipes, typically 11no. on each side of the hangar. Refer to Sect 7.2 for additional generic description of the multi-pitch roof arrangements and valley gutters. 8.2 PROBLEMS The original mild steel gutters have lasted well but will now have normally exceeded their useful life, with corrosion sometimes having perforated right through the steel plate. Gutters are prone to blockages due to self-sown vegetation, wind-blown debris, dead birds and dropped maintenance items. In the event of a blockage or short periods of high rainfall, the original roof and gutter design allows a surcharged gutter to overflow under the edge of the roof into the building. With the multi-pitched roof arrangement, this problem can result in water spillages anywhere in the hangar. In addition, with no local widening to form a tapered hopper-head at the tops of the down-pipes, the outlet flow is limited and the gutter-efficiency reduced. In order to generate the discharge required of high flow conditions, the gutter fills to a greater depth and the freeboard is much reduced. It has been known for inappropriate and poor maintenance work to have laid bitumen sheet over some rainwater outlets, thereby forcing the stormwater discharge to flow through a reduced number of outlets and down-pipes. Due to the resulting lack of capacity, the gutters become surcharged and overflow into the building. Although some gutters can last perhaps 30 years, inappropriate joint sealants fail at more frequent intervals. December

50 8 Refurbishment - Gutters and drainage The original below-ground drainage needs to be maintained and kept clear. The structural adequacy of underground pipelines needs to be checked and their capacity ascertained as part of any major refurbishment work. 8.3 GUTTER PROPOSALS Gutter renewal periods usually differ from the roof coverings, however, gutter replacement by itself is often disruptive to an existing roof construction. Where roof replacement/refurbishment is carried out it is recommended that gutter replacement is done at the same time. 8.4 GUTTER MATERIAL OPTIONS The main materials for gutter replacement are: coated galvanised mild steel (original gutters lasted for about 40 years; modern gutters are low cost but thinner with design lives of 10 to 25 years, low cost) aluminium (25 to 40 years, medium cost, needs good detailing and workmanship to avoid bimetallic corrosion and to allow good provision for expansion) stainless steel (expensive, 60 years plus) glass reinforced plastic (GRP), as a replacement or relining to existing single ply membrane, integrally with the roof system (material option A), also needing decking and side support reinforced bitumen or felt lining (short term) is effective for the short term only, perhaps for 5 years and not more than 10 years and should only be considered when an Option R4 Patch and Repair solution is being used. All relining work needs good workmanship and supervision. All options are susceptible to impact damage, and use of snowboards will assist to protect; stainless steel has best resistance, then steel but coating/galvanising is susceptible and if damaged will reduce lifespan. Design life is also governed by sealant durability and workmanship. It is very rare for sealant to last 20 to 30 years. Coated galvanised steel is the preferred option for a traditional gutter. The use of a single ply membrane as an extension of roof material option A is equally applicable. Care is also needed in selecting an appropriate joint sealant, for which manufacturer's recommendations should be followed. Joint sealants need care in its specification and, workmanship on site. Provision should be made to accommodate thermal expansion of long gutter lengths. 40 December 2001

51 8 Refurbishment - Gutters and drainage New gutter designs should incorporate adequate insulation to satisfy building regulations, reduce heat losses, and to stop condensation which causes internal dripping and can initiate corrosion. Composite insulated gutters will reduce the gutter capacity due to the thickness of the insulated gutter wall. 8.5 GUTTER ARRANGEMENT There are two main alternatives for the perimeter gutter arrangement Renewal or re-use of existing internal down-pipes Improve gutter system with the following: provide tapered hopper-heads with rounded edges, to improve discharge capacity incorporate gargoyle-type overflow pipes to stop the gutter overtopping into building in conjunction with the single ply membrane roof option, dress the membrane in and around the gutter to form a sealed lining, thus, removing the provision for overtopping into the building renew the internal down-pipes. Consideration may also be given to providing a siphonic system to improve the discharge capacity and reduce the number of down-pipes required. As the below-ground drainage would also need renewing to cater for the increased flows, this option can appear expensive. However, the underground drainage may be in need of major replacement due to other deficiencies. Snowboards and supports Gutter flashings. Existing timber on new metal zed purlin. Remove existing gutter and replace with preformed insulated metal gutter or single skin galvanised gutter and seal all joints. Existing gutter support frame. Form 6no gutter overspill shutes. Existing parapet construction either concrete, brick or cladding on steel frame. Figure 8.1 Parapet gutter detail (edge protection not shown) December

52 8 Refurbishment - Gutters and drainage Gutter screwed to packing pieces at 900 centres or fixed in accordance with manufacturer's instructions. Snowboard. Gutter flashing Remove existing gutter and replace with preformed insulated m etal gutter or single skin galvanised gutter. Remove existing packing and replace with new tanalised packing to suit falls. Figure 8.2 Typical section through Valley Gutter Provision of new external down-pipes Discharge parapet gutter through the parapet into external hopper-heads and provide new down-pipes external to the wall, discharging to new below-ground drainage. Where an annex is adjacent to the hangar, a new horizontal pipe may be provided external to the wall, to collect stormwater from the down-pipes for disposal at each end. In this case, new below-ground drainage will be required to cater for the downpipe discharge at each of the four corners of the hangar, as the current drainage layout collects stormwater centrally in the middle of each side wall. Alternatively, the external hopper-heads at high level could be connected to the existing internal down-pipes via new swan-necked pipes. Again a siphonic system may be feasible as the existing below-ground drainage will require renewing for this option, as discussed above. 8.6 SNOWBOARDS The original snowboards (also known as duckboards), were constructed in timber. It is recommended that a system of snowboards is also retained for either arrangement. Their purpose is threefold. Firstly, as the name suggests, they prevent a build-up of snow in the gutter. Any snow in the gutter is less likely to contribute to blockages and resultant roof leaks. Secondly, snowboards provide protection to the gutter from damage due to foot traffic or movement of equipment and tools during maintenance, for which the gutter is not always designed. Thirdly, snowboards limit the build-up of wind-blown or dropped debris which would otherwise require more frequent maintenance to clear blockages. 42 December 2001

53 8 Refurbishment - Gutters and drainage The original timber boards are likely to need renewal or replacement. For ease of gutter maintenance, snowboards should be as light as possible to aid their handling, but with adequate means to resist the danger of wind uplift or becoming dislodged and causing a trip hazard. Suitable materials are timber, glass-reinforced plastic (GRP), UPVC, aluminium or steel, the latter being rather heavy. For lightweight ease of use and minimum maintenance, UPVC snowboards are likely to be the most cost-effective in the long term. Various means of support are possible, but care is needed to ensure that the gutter flow is not hindered: straps can be used to span across the gutter onto local purlins at centres to suit snowboard strength and local bearing solutions the snow boards can be designed to span across the gutter sitting directly on the roof edge stools can be provided to sit directly in the gutter, but of a thin profile to minimise restrictions on a free-flowing gutter. The flat roof option R1 removes all valley gutters and thereby reduces the total length of all gutters and associated snowboards from 670m to 167m. With a single ply membrane or standing seam aluminium extended across the roof edge and dressed fully around the gutter surface, consideration can be given as to whether snowboards are needed. Full access requirements need to be addressed, as there may be a need to attend to lighting, antenna or other equipment attached to the hangar roof. (See Section 12). Where there is a desire to retain the existing sloping timber boarding and asbestos cement sheeting, the opportunity can be taken to consider use of walkways which form a physical barrier to prevent people falling through any fragile membrane adjacent to the valley gutter. 8.7 BELOW-GROUND DRAINAGE The condition of the drain runs and manholes should be checked. This may include a visual check plus close circuit television video footage appropriate to the diameter involved. It is advisable to ensure that the drain runs are cleaned prior to any CCTV survey. December

54 8 Refurbishment - Gutters and Drainage 44 December 2001

55 9 Refurbishment - Windows 9.1 DESCRIPTION The original windows were of steel frames which in many cases have been replaced by Profilit glass units. The typical variations are: 1934: A window panel approximately 6.2m long by 4.4m high within each 7.62m structural bay occurring wholly within a brickwork or reinforced concrete wall requiring support by a R.C. lintel. With concrete walls, the lintel is formed integrally within the wall. 1938: Window panels are set about 3m high but of varying length either 13.4m or 21.4m long running across two or three structural bays. There is no lintel support as the walls are constructed only to the top of the windows, above which the hangar is framed in steel and originally clad in asbestos cement sheeting. 9.2 PROBLEMS 1. Differential movement between the glazing and the surrounding structure. The causes are: a) thermal movement of the glass, window frame and wall material at varying rates b) concrete shrinkage c) brickwork expansion due to moisture absorption d) corrosion of steel window frames, and e) inadequate provision of movement joints in the walls. Because of the rigid and brittle nature of glazing along with the old window design, maintenance problems are inherent. 2. Internal lighting conditions: Although natural lighting may have been an original assumption, it will not always provide an ideal working environment. The lighting levels vary ie. sunlight to complete darkness at night. Brilliant sunshine can be dazzling and causes shadows giving an uneven lighting distribution unsuitable for some types of working. Sunlight intensity is both variable and unreliable, the contrasting pattern of bright and shadowed areas alters during the day. Artificial lighting still remains necessary. 3. Heat losses due to inadequate old windows. 4. Absence of a means of controlling ventilation by opening windows. 5. Poor access for maintenance and cleaning. December

56 9 Refurbishment - Windows 6. Doubts about the ability of existing windows to withstand local wind loading. 9.3 PROPOSAL FOR WINDOWS The Statement of Requirement (SOR) for a refurbished hangar will need to identify activities to be undertaken within the hangar. This will dictate the type of lighting required and the heating and ventilation requirements. If natural lighting is required, it should be specified in the SOR with the knowledge of its effect on the cost of window provision, window maintenance and any associated access requirements. If natural daylight is not required for specific work tasks within the hangar it is recommended that windows are not installed during refurbishment of buildings. An Investment Appraisal will need to identify the additional cost of providing natural lightning and justify its use. With modern high efficiency lighting, any additional energy required to light the building will be compensated by the increased thermal efficiency of the building, however it should be noted that attention to roof heat losses will provide even greater scope for reduction. The security classification of the hangar will address the need for anti-blast glazing. The glazing specification for new or major replacement work should consider DE DMG 02, Glazing Standard for MOD Buildings Subject to Terrorist Threat. For any chosen window option, it will be necessary to examine the long term costs in use, both operationally in terms of energy usage and in terms of maintenance and repair. There are four options available: Option W1 Option W2 Option W3 Option W4 Remove existing and provide solid infill, or overclad with suitable insulated opaque cladding. Remove existing and replace with translucent wall cladding or multiwall polycarbonate sheeting with suitable light diffusion, thermal and durability characteristics. Remove existing window and replace with, perhaps, double glazed units in appearance similar to existing. Retain existing windows if condition permits, and repair. Strengthen if required. Option W1 Will provide the best value for money solution unless other options are specifically required in the SOR. Options W3 and W4 are available, but these are not recommended. Annex G provides: 1. a summary of the advantages/disadvantages of each window option 2. illustrative detail of Option W2 - overcladding solutions for polycarbonate or translucent sheeting 3. illustrative detail of Option W4 - strengthening of existing glazing 4. detail of overcladding at existing window positions. 46 December 2001

57 10 Refurbishment - Walls 10.1 DESCRIPTION The construction and elevational appearance of the existing walls varies, depending on the hangar version, date built and occasional local variations. The main side walls of early 1934 versions were built in brickwork, and stone has been used for hangars in some area. There are cases where the masonry has been rendered. Reinforced concrete was used for the hangar walls, for the majority of 1938 versions. 250 reinforced concrete wall or 450 solid brickwork 125 reinforced concrete wall or 279 cavity brickwork Existing windows. Vertical asbestos cladding Single storey annexe Single storey annexe 254 reinforced concrete wall or 279 cavity brickwork (335 solid wall abutting annexe) Reinforced concrete wall 1934 HANGAR 1938 HANGAR Figure 10.1 Side Elevations as Existing 10.2 REINFORCED CONCRETE The reinforcement is regarded as mainly for anti-crack purposes and is not normally of major structural significance. The exception to this is the framing around door and window openings, and the bottom 1.5m of the R.C. walls which are designed to span between pad foundations. In contrast, masonry walls bear on strip footings. Asbestos cement cladding was used above the doors in the end walls of 1934 versions, and above the windows in the side walls of 1938 versions. December

58 10 Refurbishment - Walls 10.3 DETERIORATION OF WALLS Masonry/ Brickwork Concrete Cladding This can vary significantly depending on the brick type used and the degree of exposure to local atmospheric and environmental conditions. With good periodic maintenance work, many walls should continue to serve their purpose. Others will need more extensive treatment with possible areas of rebuilding. Due to the poor grade of concrete used in construction and the lack of adequate cover to reinforcement, many hangars have concrete walls with cracking and spalling. The reasons for deterioration should be determined. Spalled concrete can cause problems for aircraft and is a safety hazard to personnel below. In many cases, the existing sheeting is nearing the end of its useful life. Repairs to asbestos cement sheeting can present a health hazard ALTERATIONS Caution is required when making structural alterations to hangars or annexes with concrete walls. It is essential to remember that unlike masonry walls which bear on strip footings, the R.C. walls are designed to span between individual column foundations. The R.C. wall beneath an annex window acts as a beam and, therefore, the structural significance of window enlargement, or conversion into a door opening, should be considered. The original construction provided inadequately for movement in masonry and concrete walls. This cause of cracking and spalling may be addressed during refurbishment TREATMENT OF EXISTING CLADDING Replace existing cladding with suitable insulated cladding. The areas of wall originally clad in sheeting differ according to the hangar version: 1934: sheeted at both ends of hangar along its full width above the main doors. 1938: both sides of hangar sheeted along its full length above the windows PROPOSALS FOR SOLID WALLS In order to determine the repairs required, it is important to undertake preliminary investigatory work to identify or confirm the causes of any deterioration. Failure to do this leads to inappropriate remedies at unwarranted extra cost to the client. Symptoms such as concrete spalling and cracking can result from various causes, and for the correct treatment to be used, the cause should be clearly identified. Some degree of local material repair is usually necessary, together with other preventative action. Material repair alone is rarely economical for large areas. 48 December 2001

59 10 Refurbishment - Walls Masonry repairs Material repairs alone are rarely economical for large areas, other preventative measures are usually required such as over-cladding. Where masonry repairs are feasible, care is required in matching new mortar with the existing. The use of inappropriate mortars, very often, has a detrimental effect on the wall, as follows: a) a poor colour match can make repair patches stand out like "sticking plasters" with large numbers of repairs giving the wall a patchwork appearance. b) the wrong blend of mortar constituents can actually cause long term damage to the wall, often accelerating the rate of deterioration. Ordinary modern mortars are usually stronger than the original due to the properties of modern cement, and can cause the following situations: 1. repair patches are stronger than the locally surrounding wall and so have less ability to accommodate movement. Future movement is then limited to adjacent weaker areas of wall, thereby increasing the likelihood of cracking and the rate of deterioration in these areas. 2. normal modern mortar is usually less breathable than the original lime mortar and its use often impairs the behaviour of the masonry resulting in surface "blows" or disintegration. Use of traditional lime mortars is often necessary. Repairs to reinforced concrete walls The guidance given in the following BRE publications should be considered: Corrosion of steel in concrete BRE Digest 444 Parts 1, 2, & 3 Feb 2000 Repair and maintenance of reinforced concrete Currie & Robery 1994 Corrosion Damaged concrete Pullar-Strecker CIRIA 1987 Walls All external walls of a building envelope should be designed so as to provide the following: a weatherproof skin thermal insulation as required by the Building Regulations physical security resistance to impact damage. Wall cladding The criteria for choosing a wall cladding system and the range of materials, finishes and insulation available are much the same as for roofing. Some variations are possible: structural steel liner trays can be added, providing a flush inner wall it is necessary to ensure that any core material has appropriate fire resistance some cladding systems have the option of an industrial grade plasterboard, or composite plasterboard/insulant inner lining. These materials are not regarded as durable enough for most hangar facilities. December

60 10 Refurbishment - Walls Over-cladding of walls External cladding is the recommended solution for deteriorated concrete and masonry walls. The cladding serves at least three purposes: protection of the concrete from the weather and atmospheric borne agents of corrosion improvement to the insulation characteristics of the building protection of personnel from falling pieces of spalled concrete The causes of deterioration must first be established and remedial works carried out before any decision is taken. New wall sheeting to overclad New wall sheeting to overclad existing solid walls with existing solid walls with translucent sheeting across window ranslucent areas sheeting across window areas. New wall cladding to replace existing and extend to overclad existing solid wall. Translucent sheeting across window areas. Single storey annexe Single storey annexe 1934 HANGAR 1938 HANGAR Figure 10.2 Side Elevations as Proposed Flat roof option Lower dado walls The lower dado walls provide: appropriate physical security against unauthorised entry (refer also to Sect 13.4) simplicity for internal fixings simplicity or repair in the event of accidental damage greater ease of fire compartmentalisation. A fully engineered design may dictate forms of construction commensurate with the heights involved. Guidance on the selection and suitability is provided in BRE Report 262 Thermal Insulation Avoiding Risks. These walls should comply with the requirements of the Building Regulations in respect of structural stability, resistance to damp penetration and thermal performance. Increases in the height or thickness of walls may be dictated by acoustic considerations, the requirements for fire compartmentalisation, or levels of increased security for specialist Units. Care should be taken with the detailing, specification and construction of masonry walls, particularly in areas susceptible to conditions of driving rain. Movement joints should be provided in accordance with BS 5628 Code of Practice for the Use of Masonry. 50 December 2001

61 10 Refurbishment - Walls Guidance publications: BRE Information Paper 19/81. Assessment of Hard Body Impact Resistance of External Walls. BRE Report 262 Thermal Insulation; Avoiding Risks. Re-alkalisation of concrete This process restores carbonated concrete to its original alkaline state, which is necessary for the protection of reinforcing steel. It can be very expensive, however it is said to be economical in the long term. Corrosion protection (CP) systems These can also provide very effective means of controlling corrosion of the reinforcement, but again can be expensive to set up. In the long term, this system is inexpensive to operate and can use remote controls, ideal for sites with access difficulties. For hangars, solutions other than CP are regarded as more costeffective. Summary of wall repairs Walls are not usually considered to be critical structural elements which might warrant CP systems or realkalisation. A system of basic repairs, anti-carbonation coating and overcladding is regarded as the most effective. December

62 10 Refurbishment - Walls 52 December 2001

63 11 Refurbishment - Doors 11.1 DESCRIPTION There are six sliding and overlapping steel doors at each end of a typical Type-C hangar. Each door measures approximately m high by 8m wide and weighs in the order of 12.5T, comprising a steel frame clad in steel plate. The doors run on cast iron wheels in tracks set into a reinforced concrete footing. The tops of the doors run between guide rails which also provide lateral restraint. Originally, the cavity between the sheeting was filled with gravel, although there was an instruction in the 1950s to remove the gravel to reduce the load on the wheels PROBLEMS Water has leaked into the doors, resulting in corrosion of the door frame and the plates, exacerbated by the lack of ventilation in the door cavity and retention of water by the gravel infill. Expansion due to corrosion has occurred causing the plates to bow out between the fixing bolts or studs, leaving rust-filled gaps between the frame and the plate. Around the edge of each plate these gaps allow further water penetration, thereby, aggravating the situation, particularly around the perimeter of the doors. The wheels and tracks have worn and corroded, often by 10 mm or more. The lower tracks collect debris which can cause derailment. Health & Safety Warning Notice 01/02 identified the shearing and corrosion of members providing upper level lateral support to the door. Subsequent investigations has indicated dubious shimming arrangements to the upper level lateral support bracket, often involving a 150mm depth of shims. It is recommended that this detail is reviewed as part of any refurbishment. The upper guide rails have also corroded particularly at the fixing brackets and bolts where the rails are formed by channels lying flat or I-sections. Water and debris collects on the exposed web and is contained by the upturned flanges. In some cases this has been eased by the drilling of holes through the web, but the arrangement remains poor. Due to wear and tear, corrosion, and a lack of maintenance, fixtures at height have been known to loosen and fall creating a dangerous hazard. These items include door stops, buffers, wheels and draught excluder strips. With a combination of some of the above situations and in certain wind conditions, the lateral stability of a door may be at risk. If a roof is subject to wind uplift, the top guide rails will deflect upwards with the roof structure to which they are attached. December

64 11 Refurbishment - Doors 11.3 DOOR OPTIONS There are various options which will vary depending on the site specific requirements. Generally these are: Option D1 Retain repair and refurbish existing doors. Maintain existing arrangement with the steel plates on the front and rear faces. Refurbishment can include provision for either: A. Manual operation B. Automatic operation Option D2 Provide new doors similar to existing with automatic operation. Option D3 Do nothing (rarely suitable due to deterioration of the door). Where there is no specific requirement to retain the door or where the opening size may be reduced the following may apply. Option D4 Decommission but retain as a structural wall. Figure 11.1 indicates this option. Option D5 Remove existing doors and infill. Figure 11.2 indicates this option. In options D4 and D5 the opportunity can be taken to introduce smaller roller shutter doors or up and over industrial doors as illustrated in Figs 11.1 and Option D6 Remove existing doors, infill partially and provide reduced height and/or width doors commensurate with the ability to retain access for aircraft involved eg. helicopter hangerage may not require full height access doors. It is recommended that an option study identifies the separate alternatives of manual or automatic operation. Risk assessments of the use of existing, refurbished and new doors should be included in the option study. Further details of Options D1 to D6 are provided at Annex H. It is recommended that the temporary loading conditions be considered fully when considering complete removal of doors. Adverse structural consequences to roof members can arise in certain circumstances and these must be managed out DOOR INSPECTIONS Doors require regular inspection and maintenance to prevent deterioration. The gravel infill, if still in place, should be completely removed. They should be fully operational whilst ensuring that all means of access to a building remain safe. It is known that the door plates are an integral part of the door structure. Therefore, no modifications to the door structure are to be carried out, without first carrying out a comprehensive analysis taking into account the door structural members, bracing and plating etc, and the site specific loadings. 54 December 2001

65 11 Refurbishment - Doors The door top guides, supporting brackets, door stops, bottom tracks etc, are all an integral part of the door system, which also require regular inspection and maintenance. For further details and guidance, reference should be made to DE Technical Bulletins 99/29 and 99/30, and DE Health and Safety Warning Notice 01/ HANGAR DOOR OUTRIGGER STRUCTURES These are typically exposed steel latticed frames, supporting the door top guides, located on either side of the doors, to allow the doors to fully open giving full width access in to the hangar. The top door guides are usually beam or channel sections, positioned horizontally. This arrangement allows debris and water to collect in the horizontal webs. This area needs to be checked for debris and corrosion. Small holes can be drilled in the webs at regular centres, to allow surface water to drain away. Ensure that the holes are painted, or corrosion will take place. The frame sections and the corrosion protection needs to be checked, and for any physical damage, at ground level, If any physical damage is found, then repairs are to be carried out, and consideration is to be given to the provision of protection bollards around the frames. The outrigger lattice frames are subject to high wind loads, when the doors are in the open position, and as such, high uplift forces can be generated, and are resisted by the foundation holding down bolts. This condition should not normally occur, as the doors should be closed when high winds are forecast. Nevertheless, the projecting holding down bolts, and the frame base plates, which are usually located just above ground level, are to be regularly inspected for corrosion and damage. Repairs to corroded sections usually involve removing existing paint finishes and welding plates or suitable sections, to achieve full section properties. The paint finish is to be re-instated to the repair areas, or the whole of the exposed frame and door guides can be re-treated with a suitable system BLAST AND FRAGMENT PROTECTION As stated in 11.1, the cavity of the door structure was originally gravel filled to provide this protection, which was subsequently removed. However, if there is a requirement to reinstate this protection, as part of any refurbishment, then advice should be sought from the Protected Buildings and Weapon Effects (PBWE) section of Defence Estates. Contact: Protected Buildings and Weapon Effects Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL Tel: Fax: December

66 11 Refurbishment - Doors Remove existing door gantry or retain for possible recommissioning of doors. Vertical profiled cladding to 1934 hangars, pitched roof sheeting to 1938 hangars. New insulated profiled metal cladding on new sheeting rails, as infill over doors. Hangar doors moved aside and permanently secured in position and decommissioned. New roller shutter or up and over industrial door. End Elevation Existing doors fixed in position as permanent cladding Figure 11.1 Door Option 4. Decommissioning of hangar doors but retention as structural wall Vertical profiled cladding to 1934 hangars, pitched roof sheeting to 1938 hangars. Existing doors removed and replaced with new insulated profiled metal cladding on new sheeting rails. Existing redundant door gantry may be removed as opposite side. Personnel Door New roller shutter or up and over industrial door. End Elevation Existing doors removed and replaced with new cladding Fig 11.2 Door Option 5 Remove existing doors and infill. 56 December 2001

67 11 Refurbishment - Doors 2 / 3 1 /2" x 2 1 /2" x 1 /4" 4 / 5" x 41 /2" x 18 lb/ft BSB roller guides Top guide roller. Steel plate doors. Cast steel wheel. Rolled steel bottom rail r.c. foundation. Figure 11.3 Section through top and bottom door guides December

68 11 Refurbishment - Doors 58 December 2001

69 12 Roof access 1. It is MOD policy to comply with the 1974 Health & Safety at Work Act, the Workplace (Health, Safety and Welfare) Regulations 1992, the Management of Health and Safety at Work Regulations 1999 and the Construction (Health, Safety and Welfare) Regulations Regulation 13 of the Workplace (Health Safety and Welfare) Regs provides guidance on falls or falling objects eg. para (1). para (3). So far as is reasonably practicable, suitable and effective measures shall be taken to prevent any event specified in para (3). The events specified in this paragraph are: (a) any person falling a distance likely to cause personal injury. (b) any person being struck by a falling object likely to cause personal injury." 3. Access to the roof is to be determined by hazard identification and risk assessment. The risk assessments should include a consideration of the competence of the personnel involved, the tasks on which they are engaged and the likelihood of slipping, falling, the presence of fragile materials, etc. 4. It is generally not economic to provide 365 days access to untrained people. It is recommended that suitably trained/screened people are to be used for various activities. (a) (b) for routine pre planned works purposes access, is preferably restricted to daylight hours when conditions are not windy, icy or wet (wind speed to be identified in risk assessment). User requirements over and above (a) will dictate commensurate enhanced provision eg. access works and/or better calibre of personnel. 5. The property management system under DE Specification 005 indicates that technical inspection are required every 2 years, and therefore, appropriate access is required to ensure that a meaningful visual inspection can be made of the roof. 6. External lights, antennae and lightning protection are often installed on roofs and these may dictate more frequent inspections. The additional costs of these activities should be identified at Option Study stage. 7. Work to the roofs may be identified during the technical inspections. In addition work may be programmed on a periodic basis eg. cleaning of clear roof panels, valley gutters, outlets, etc. December

70 12 Roof access 8. Guidance on roof working is available in HSE publications. (a) (b) HSG 33:1998 Health and Safety in Roof Work. HSE HSG I5O: 1996 Health and Safety in Construction. HSE 9. Method of access must be recorded for each major structure and the Property Manager must ensure that this information is kept within the Master Index and is made available for any person needing to go on to the roof. The Method of access record should be prepared either at (a) the time of need (b) the next professional appraisal (c) the time of project or works service involving a refurbishment (eg. to meet CDM requirements). 10. Flat roofs (up to 10 degrees slope) Where there is no need to inspect perimeter gutters or the perimeter from the roof, permanent means of protection need not be provided. 11. Roofs (above 10 degrees slope) Provision is to be made for permanent protection eg. by edge protection and/or work positioning devices or fall arrest devices. The means of permanent protection must be commensurate with the competences and knowledge of the personnel requiring access. For instance, if a suitable system of body harness is required to undertake the work this dictates a level of competence and underpinning knowledge only demonstrated by a defined class of personnel. Refer to DE Technical Bulletin 00/06 Fixed Access Ladder Systems and SRP 07 Safety Rules and Procedures For Working at Height. 12. Damage can be caused to the roof surface by incorrect footwear and inappropriate sharp or heavy objects. As examples, single ply membranes can be punctured or the protective coat to steel sheeting can be violated. 13. Warranties Installers and manufacturers warranties/guarantees can be invalidated by people who are not made aware of specific requirements when working on roofs. A positive no blame culture must be developed to ensure that the location of any damage accidentally caused is reported to the Property Manager immediately. 14. Access to the roof Reference should be made to DE Technical Bulletin 00/06 Fixed Access Ladder Systems. In general terms the arrangements are: Ladder Type 3 used in conjunction with Working Platforms spaced at 3 metres maximum (used by general worker). Ladder Type 2 in conjunction with Access Platforms spaced at 6 metres maximum (used by an authorised worker.) 60 December 2001

71 12 Roof access Ladder Type 1 (and Rigid Rail Fall Arrest System) in conjunction with Rest Platforms spaced at 15 metres maximum (used by authorised basic climbers). 15. Access on the roof The requirements at roof level eg. provision of handrails, walkways, anchorages, will influence the decision on whether a general worker, a screened worker or authorised climbers are required. For option study purposes it is recommended that the Ladder Type 2 solution is adopted as a minimum. This will require two intermediate platforms to suit the height of 14m to eaves level, plus a top platform at eaves level. If the Project Sponsor requirement is for a Ladder Type 1 solution then this should be included at option study stage. 16. Adverse effects of access provision Wherever possible the need for access to the roof should be minimised. Numerous additions to a roof results in an increased access requirement due to a consequent additional inspection and maintenance requirements. Provision of permanent protection to meet this need eg. by edge protection, work position devices or fall arrest devices and associated fixings/anchors/eyebolts leads to an inspection requirement in itself. Unless great attention is given to the design and workmanship, the use of fixings/anchors/eyebolts can cause the watertightness of the roof to be impaired. December

72 12 Roof access 62 December 2001

73 13 Standards and regulations It is Government Policy that although the Crown is exempt from the provisions of the various Building Acts and Regulations all construction carried out on behalf of Government Departments is to comply with the substantive requirements of the relevant Acts of Parliament and Statutory Instruments, and that this compliance can be demonstrated BUILDING REGULATIONS At the present time The Crown is exempt from the substantive and procedural requirements of the Building Regulations. However it is Government policy that we comply with the substantive or technical requirements. Notice has been given that it is the intention of the Government to remove Crown exemption from the substantive requirements in the near future resulting in MOD having to comply by way of law rather than policy. The MOD has a system in place to deliver compliance with the Building Regulations. Details of this sytem can be found in Technical Bulletin 01/26 'The Method of Operation of the MOD Building Control Compliance System'. The regulations that apply to each project will be determined by location. England & Wales : Scotland : Northern Ireland : The Building Regulations 2000 (Statutory Instrument No 2531) The Building Standards (Scotland) Regulations 1990 (as amended) The Building Regulations (Northern Ireland) 1994 (as amended 1995 & 1997) The Building Regulations are not applied retrospectively but where major refurbishment works are carried out to a building, the works may be considered as a 'Material Alteration' requiring compliance with the Building Regulations. An alteration is considered material for the purposes of the regulations if the work, or any part of it, would adversely affect the level of compliance in the existing building of the following sections: Part A: Structure Part B: Fire Safety Part C: Access & Facilities for the Disabled There is an amendment proposed to the Building Regulations (England & Wales) which suggests that Part L, Conservation of fuel and energy may be added to the above list. Consideration should also be given to the requirements of the Disability Discrimination Act 1995 which may have some impact when it comes into full effect in December

74 13 Standards and regulations Further advice on compliance with Building Regulations is available from: DE Specialist Building Control Officer Defence Estates Central Blakemore Drive Sutton Coldfield West Midlands B75 7RL Tel: Fax: PLANNING AND FIRE OFFICER APPROVALS Works to the hangars which significantly affect the external appearance of the buildings, increase the volume, or raise the roof height should be notified to the Local Planning Authority (LPA) using the Circular 18/84 Notification of Development process. The area Defence Estate Advisor should also be involved with any application. Changes of use of the building may or may not require planning permission but should be notified to the LPA for a determination. Changes of use and internal layout will usually require consultation with the Fire Prevention Officer as they are likely to alter means of escape provisions and the fire risks of the new use may be greater or less than existing CROWN FIRE STANDARDS It is expected that each site will be subject to a Fire Risk Assessment Methodology (FRAM) analysis to determine the minimum levels of Fire Protection provision. Crown Fire Standards and, in particular, Fire Standard E10 - Aircraft Hangars are mandatory for all new build hangars and they are to be applied, so far as is reasonably practicable, when major refurbishment or modernisation of hangars is carried out. The Crown Fire Standards are not however retrospective and, where for example, only limited renewal works items such as roof cladding are carried out, then only that element of the works is required to comply with the Standard. It should be noted that the relevant Crown Fire Standard to be applied is determined by the proposed use of the hangar building and not by what it was built for originally. Therefore, Crown Fire Standards E9 - Vehicle Workshops and Storage, Garages and Car Parks or E11 - Storage Premises may be relevant Fire Standard. Further advice on compliance with the respective Fire Standards is available from: Senior Fire Prevention Officer Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL Tel: Fax: December 2001

75 13 Standards and regulations 13.4 HEALTH AND SAFETY It is MOD policy that all works fully comply with relevant Health and Safety legislation. The guidance provided in JSP 375 the MOD Health and Safety Handbook should be followed The Health and Safety at Work etc. Act 1974 The main purpose of the Health and Safety at Work etc. Act is to secure the health, safety and welfare of people at work, and to protect others against risks arising out of those work activities. The Act also controls the keeping and use of explosive, highly flammable or other dangerous substances. The Act is supplemented by Health and Safety Regulations, of which the following are particularly relevant to MT facilities: Workplace (Health, Safety and Welfare) Regulations 1992 Provision and Use of Work Equipment Regulations 1998 Manual Handling Operations Regulations 1992 Management of Health and Safety at Work Regulations 1999 Health and Safety (Safety Signs and Signals) Regulations The Construction (Design and Management) Regulations 1994 (As amended by the Construction (Design & Management) Amended Regulations 2000). These regulations do not supersede the Health and Safety at Work etc. Acts, but place new duties upon clients, their agents, designers and contractors to take health and safety issues into account and co-ordinate and manage them effectively throughout all stages of a construction project, from the inception to the completion of the work on site and subsequent operation, maintenance and repair. The following DE Technical Bulletins should be referred to: TB 95/23 TB 95/24 Health and Safety CDM Regulations 1994 as applied to projects Health and Safety CDM Regulations 1994 as applied to Property Management TB 95/24 Addendum to Technical Bulletin 95/24 Further advice on compliance with the above documents is available from: DE Health and Safety Officer Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL Tel: Fax: Control of Substances Hazardous to Health Regulations 1994 (COSHH) The aim of the Control of Substances Hazardous to Health Regulations is to provide protection from the effects of work with substances hazardous to health. These substances range from common materials such as cement or paint, to those which may be present on a site, such as toxic materials in the soil or silica in masonry. December

76 13 Standards and regulations 13.5 PHYSICAL SECURITY During any refurbishment project, the Project Sponsor must give consideration to physical security. Guidance to Project Sponsors, Property Managers and security officers on the methods of obtaining security assistance and advice for works services is given in JSP 440, Vol 1, Chapter 5. The design of new walls should comply with the requirements of the Building Regulations in respect of structural stability, resistance to damp penetration and thermal performance. The security class of the building, as well as its liability to terrorist attack, may affect the type and strength of glazing required in any works where windows, doors or glazing are proposed to be replaced. DE Design and Maintenance Guide 02 - Glazing Standards for MoD Buildings subject to terrorist threat is a mandatory document if the building is assessed as being at risk ENVIRONMENTAL LEGISLATION It is MOD policy to comply with the Environmental Protection Act 1990 and other relevant legislation. The guidance provided in JSP 418, the MOD Environmental Manual, should be followed. 66 December 2001

77 Annex A Record of drawings a) CAD drawings of typical detail drawings and sketches: Drawing No. Title DE/H1/001/101 C Type Hangar - Gabled (1934) GA Original Drainage DE/H1/001/102 C Type Hangar - Gabled (1934) Foundation Plan DE/H1/001/103 C Type Hangar - Gabled (1934) GA Plans and Elevations DE/H1/001/104 C Type Hangar - Gabled (1934) GA Steelwork Layout DE/H1/001/105 C Type Hangar - Gabled (1934) Main Truss A Details DE/H1/001/106 C Type Hangar - Gabled (1934) Secondary Truss Details DE/H1/001/201 C Type Hangar - Hipped (1938) GA Original Drainage DE/H1/001/202 C Type Hangar - Hipped (1938) Foundation Plan DE/H1/001/203 C Type Hangar - Hipped (1938) GA Plans and Elevations DE/H1/001/204 C Type Hangar - Hipped (1938) GA Steelwork Layout DE/H1/001/205 C Type Hangar - Hipped (1938) Main Truss A Details DE/H1/001/206 C Type Hangar - Hipped (1938) Secondary Truss Details December

78 03 - Type C hangar Annex A Record of drawings 68 December 2001

79 Annex A Record of drawings Annex A Record of drawings (b) Drawings held on microfiche at DE - Hangar Type: C Cat Microfilm Drawing Hangar Drawing Title No Number Number /34 C: Calc for main stanchions, door trestles grantry girders and foundations /34 C: Calc for Roof girders /34 C: Stress Diagrams for Roof and Wind girders /34 C: Load Diagrams and Calc for Roof Trusses /34 C: Calc for Wind Girders, Vertical Bracing /34 C: Roof Trusses /34 C: Gables Frames, Stanchions, Founds, Bracings /35 C: Timber Purlins /35 C: Horizontal Wind Girder A/35 C: Horizontal Wind Girder /35 C: Roof Trusses /35 C: Roof Girders E /35 C: Roof Girders E /35 C: Roof Girders A/35 C: Roof Girders /35 C: Vertical Bracketing /35 C: Main Stanchions /35 C: Gullerbearer and Runway Beams /35 C: Purlin Details, Deats /35 C: Top Door Guides and Canopy /35 C: Door Trestles and Box Girders /35 C: Top Door Guides and Canopy /35 C: Gen Arrangement /35 C: Gable Framing /35 C: Gutters Bearers /35 C: Gutters /35 C: Corner Stanchions /35 C: Elevations and Details of Steel Windows /35 C: Elevations and Details of Steel Windows /35 C: Sprocket Wheels for MSD /35 C: Hip Rafters /35 C: Rafters and Comp d Tie Beams in Gables /35 C: Annexes - HB Squadron /35 C: Annexes - AC Squadron /35 C: Concrete Construction /35 C: Drainage /35 C: Concrete Construction /35 C: Arrangement and Drainage /35 C: HB Squad - Concrete Construction December

80 03 - Type C hangar Annex A Record of drawings /35 C: HB Squad - Concrete Construction /35 C: Light Bomber Squad - Concrete Construction /35 C: Fighter Squad - Concrete Construction /35 C: A T Squad - Concrete Construction /35 C: A T Squad - Rein Concrete Design /35 C: A T Squad - Rein Concrete Design /35 C: A T Squad - Rein Concrete Design /35 C: A T Squad - Rein Concrete Design /36 C: Main Girders, Wind Girders /36 C: Gearing Rails for Gravel Filled S D /36 x 2 C: MSD /36 C: Found to Door Rails * /36 C: Travelling Wheels /36 C: Operating Gear, Brackets and Rollers MSD /36 C: Cocking Attach, MS Rails, Timber Buff /36 C: MSD /36 C: Founds for Steel Door Rails * /36 C: Founds for Stanchions and Door Trestle /36 C: Concrete Construction /36 C: Shed Wall Reinforcement /36 C: Rein Concrete Design / /36 C: Shed Wall Rein /36 C: Staircase Details /36 C: Staircase Details /36 C: Staircase Details /35 C: Staircase Details /36 C: Heating Pipe Ducts /36 C: Extra Wall Rein /36 C: HB Squad - Shed Wall Rein /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Shed Wall Rein /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /36 C: HB Squad - Rein Concrete Design /35 C: Annex: Flying T Squad - Concrete Cons /36 C: Annex: Flying - R C Wall Details /36 C: Annex: Flying - R C Wall Details /36 C: Annex: Flying - R C Wall Details /36 C: Annex: Flying - Shed Wall Rein /36 C: Annex: A C Squad - Plan Part Annex /36 C: A T Squad - Concrete Construction /36 C: R C Squad - Rein for Nor Prot /36 C: R C Squad - Rein for Nor Prot /36 C: R C Squad - Rein for Nor Prot /36 C: Concrete Construction /36 C: Rein in Stanchion Casing /36 C: Rein in Wall Beams * /36 C: Concrete Construction * /37 C: Erecting Shed 70 December 2001

81 Annex A Record of drawings /37 C: Rein for Normal Prot /38 C: Erecting Shed /36 C: Erecting Shed /36 C: Rein for Norm Protection /36 C: Rein for Norm Protection /36 C: Shed Wall Reinf /36 C: Rein for Norm Protection /36 C: Erecting Sheds /36 C: Erecting Sheds /36 C: Shed Wall Reinf /36 C: Erecting Sheds /36 C: Elevation /36 C: Shed Wall Details /36 C: Shed Wall Elevations /36 C: Shed Wall Rein F T Squad /36 C: Rein Norm Protection /36 C: Rein Norm Protection /36 C: Annex: Rein Norm Prot - F T Squad /36 C: Annex: Concrete Const - H B Squad /36 C: Annex: Concrete Const - H B Squad /36 C: Annex: Stanchions Encasing - H B Squad /36 C: Annex: Staircase Details - H B Squad /36 C: Annex: Sections to Annex Walls - H B Squad /36 C: Annex: Elevation H B and M B Squad /36 C: Annex: Shed Wall Rein - H B Squad /36 C: Rein for Norm Prot - A T Squad /36 C: Rein for Norm Prot - A T Squad /36 C: Rein Concrete Design /36 C: Rein Concrete Design /36 C: Shed Wall Rein / /36 C: Rein for Norm Prot /36 C: Rein for Norm Prot /36 C: Rein for Norm Prot /36 C: Rein for Norm Prot /37 C: Shed Wall Elevations * /37 C: Shed Wall Details /784 67/37 C: Annexe Wall Details /785 68/37 C: Sections to Annexe Walls /786 69/37 C: Staircase Details * /37 CO/S: Gen Arrangement * /37 CO/S: Roof Trusses * /37 CO/S: Gable Frames, Stairs, Founds /37 CO/S: Main and Wind Girders /38 C Asbestos: Gen Arrangements /38 C: Founds Plan /38 C: Founds for Stanc + Door /38 C: Asbestos: Framing to Side Walls / /38 C: Framing to Side Walls End Bays /38 C: Arrangement of Steelwork to Annexes /38 C: Details of Steelwork to Annexes /38 C: M.S.D /38 C: Details of M.S.D /38 C: Gen Arrangement Door Gearing /38 C: Locking Attachment December

82 03 - Type C hangar Annex A Record of drawings /38 C: Chain Wheel for MSD /38 C: Sprocket Wheels for MSD /38 C: Travelling Wheels for MSD /38 C: Pins, Handles for MSD /38 C: Foundation Plans /38 C: Founds for Stanchions and Door Trestle /38 C: Framing to Side Walls /38 C: Arrangement of MSD /38 C: Details of MSD /38 C: Gearing, Rails for MSD /38 C: Locking Attachment /38 C: Operating Gear, Brackets + Rollers /38 C: Travelling Wheels for MSD /38 C: Steel Doors to Annexes /38 C: Sliding and Hinged Annexes /35 x 2 C: Perm Camber to Roof Girders /39 C: Steel Ties and Concrete Footings for Brick Walls /39 C: Asbestos: Gen Arrangement * 65/37 C: Shed: Stair Encasing and Beam Details * 66/37 C: Shed: Annex Wall Details /37 C: Shed: Annex Wall Details /37 C: Shed: Sections to Annexe Walls /37 C: Shed: Staircase Details * 1977/37 C: Shed: Erecting Shed * 2678/37 C: Shed: Rein Concrete * DCES/3/660A C: Hangar: Doors * XK1/1 C5: Proposed Alternative Designs * XD1/1 C34: Hip Rafters 72 December 2001

83 Annex A Record of drawings Annex A Record of drawings c) Schedule of archive drawings held at DE - Type C (1934) Hangar drawings Neg/Print Drawing Drawing Title No. P 832/34 Calculations for roof girders P 834/34 Load diagrams & calculations for roof trusses N 1584/34 G.A. N 2029/34 GA P 2029/34 G.A. N 2036/34 Annex details & section through main wall of shed N 2040/34 Annex: G.A. & foundations N 2774/34 Annexe plans & elevations N 3013/34 Details of foundations for stanchions & door trestles N 861/35 Roof trusses (2434/37) N 862/35 Roof trusses N 863/35 Roof trusses N 865/35 Roof girders N 867/35 Main stanchions (2441/37) N 872/35 G.A. P 872/35 G.A N 880/35 Corner stanchions (2447/37) P 3264/35 Concrete construction (with expansion joint on RHS of stanchions) P 3265/35 G.A. & details of drainage inside shed N 3266/35 Concrete construction N 3268/35 Concrete construction - Annexe plans & elevations P 172/36 Side Annexe - R.C. wall details P 173/36 Side Annexe - R.C. wall details P 275/36 Main sliding doors P 709/36 Foundation plan & foundations for mild steel door rails P 2955/36 R.C. design - details of shed wall reinforcement P 5046/36 Concrete construction (14 walls) - Annexe plans & elevations P 3012/34 Foundation plan & details of door rail foundations December

84 03 - Type C hangar Annex A Record of drawings Annex A Record of drawings d) Schedule of archive drawings held at DE - Type C (1938) Hangar drawings Neg/Print Drawing Drawing Title No. N 9180/38 G.A. N 9181/38 Foundation plan & details of door rail foundations N 4262/39 Main stanchion topcliffe (2386/37) N 4263/39 Roof girders A & D - Topcliffe (2387/37) N 4264/39 Roof girders E - Topcliffe (2388/37) N 4265/39 Roof trusses N 4266/39 Roof trusses - Topcliffe (2390/37) N 4267/39 Roof trusses - Topcliffe (2391/37) N 4275/39 Hips -Topcliffe (2396/37) N 9267/39 Foundation plan & door rail foundations 74 December 2001

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97 Annex B Change Suggestion Form Defence Estates Wind Sensitive Structures Specialist Services Blakemore Drive Sutton Coldfield B75 7RL Guide to World War II Hangars Hangar Guide 03 Type C Hangars Change Suggestion Form Originator: Date: Reference: Change Suggestion Section: Page: Change detail: Continuation sheet included? Y N Reason: Continuation sheet included? Y N DE Review Action: Reference: Action Date: Approved: Actioned: December

98 03 - Type C hangar Annex B Change Suggestion Form 76 December 2001

99 Annex C Hangar Notification Form HANGAR TYPE: DEFENCE ESTATES Wind Sensitive Structures Specialist Services Blakemore Drive Sutton Coldfield B75 7RL NOTIFICATION OF: (a) HANGAR RELATED PROBLEMS or (b) WORKS ON A HANGAR BUILDING or (c) EXISTENCE OF HANGAR FOR INSERTION ONTO DATABASE Height of Hangar in number of Standard Units (ie. 2 or 3 units high) MOD Establishment Name: Address: Tel No: Location of Hangar (if different from Establishment) Current Use of Hangar Building Reference Total Estimated cost of Works/Project Details of Modifications carried out to original construction: (eg. new roof cladding and purlins, modified hangar doors, etc) Description of Hangar Works/Project (or description of problem) Programme of Works/Project (include expected dates of main activities eg. option study, design, tender, construction, etc) Project Sponsor Project Sponsor Name: Name: Address: Address: Project Sponsor Name: Address: Tel No: Any Other Comments: Tel No: Tel No: Form Completed By: Name: Appointment: Date: Address: Tel No: December

100 DMG 00 Guide to World War II Hangars 03 - Type C hangar Annex C Hangar Notification Form 78 December 2001

101 Annex D For map of the United Kingdom showing the Basic Wind Speed. See the British Standard BS CP3 CHAPTER V Part 2: 1972 December

102 Annex D This page left intentionally blank 80 December 2001

103 Annex E Safe loading Attention is drawn to the contents of TB 99/29 Hangars - Safety of Structure - Recommendations for Users During Adverse Weather Conditions. During Snowfall. When freshly fallen snow reaches a depth of 200 mm, the Property Manager must advise the Commanding Officer of the possible dangers and that the hangar structure must be put under observation. If excess deflection or other signs of structural distress are noted by the EWC, the occupants should be ordered to evacuate the hangar. Depending upon the level of risk attached to the dangers and the value of stores or aircraft inside the hangar, the Commanding Officer must decide if their removal is imperative. During High Winds. When high winds are forecast, the Commanding Officer must ensure that hangar doors are kept closed. There is a risk to the safety of the structure and damage to roof cladding. High winds for the hangars listed in this Bulletin can be considered to be gusts of more than 27m/s (60mph). (NB The wind speed stated is the gust speed as against a steady wind speed). These minimum limitations apply unless there is contrary evidence based on site specific calculations. Where refurbishments materially change the building form, the project manager should provide information on the safe operational conditions. A site specific analysis gives the opportunity to determine the actual limiting gust speed that is allowable. December

104 Annex E Safe Loading 82 December 2001

105 Annex F Roofing options & description of roofing materials The various roofing options referred to in Section 7 are summarised in Fig F1. Figure F1 Summary of roofing options (see Section 7) OPTION R1 OPTION R2 BRIEF DESCRIPTION Provide new flat over-roof: using either a single ply membrane or standing-seam aluminium sheeting, including new purlins and insulation. OPTION R1 IS THE RECOMMENDED OPTION Retain existing multi-pitch roof profile: Remove existing timber boarding, and reclad with new profiled metal sheeting, purlins and insulation. FULLER DESCRIPTION OF OPTION VARIANTS Option R1A - Flat roof finished in a single ply membrane Remove all existing cladding, boarding and timber purlins, but retain the steel structure. The new roof is formed by spanning steel purlins across the existing main trusses (7.62m span) and supported on steel stub columns of varying height to create a fall of 1 in 40 (2.5%) from the hangar centre to the sides. The single ply membrane with separation fleece overlays rigid insulation board and is fixed to an under-lying profiled structural liner sheet spanning across the purlins, including a vapour control layer beneath the insulation. The liner sheeting should be galvanised for durability and consideration should be given for colourcoating the underside to improve the internal lighting of the hangar. Option R1B - Flat roof finished in aluminium standing seam sheeting For this option the stripping of existing finishes and provision of new purlins is as Option R1A. The internal liner spans between the purlins which, unlike option R1A, is largely non-structural and only provides support to the insulation, which has no requirement to take foot traffic. The external aluminium sheeting is supported by the purlins via upstanding brackets. As with option R1A, a vapour control layer should be provided, and the liner sheeting should be galvanised for durability with consideration given for colour-coating the underside to improve internal lighting. Option R2A - Existing multi-pitch profile, reclad with steel sheeting and existing timber boarding removed Remove all existing roof coverings but retain the steel structure. Reclad the existing multi-pitch profile with new built-up roof in profiled steel sheeting supported by new purlins with inner liner, vapour control layer and loose insulation. Option R2B - Existing multi-pitch profile, as Option R2A but reclad with aluminium sheeting As Option R2A removing all existing boarding etc., and retaining existing multi-pitch roof profile, but reclad with new aluminium sheeting in lieu of steel sheeting. Option R2C - Existing multi-pitch profile, as Option 2A but reclad with composite sheeting As Option R2A removing all existing boarding and retaining existing multi-pitch roof profile, but reclad with new composite cladding in lieu of built-up system. December

106 Annex F Roofing options & description of roofing materials OPTION R3 OPTION R4 BRIEF DESCRIPTION Retain existing multi-pitch roof profile: As Option R2, but retain and repair existing timber boarding. Retain existing multi-pitch roof profile: Clean, repair and coat existing sheeting with a waterproof compound. POOR VALUE FOR MONEY. FULLER DESCRIPTION OF OPTION VARIANTS Option R3 - Existing multi-pitch profile, as Option 2 but retain and repair existing timber boarding The existing timber boarding is often found to be of good quality and condition. In such cases, it may be retained as the inner liner. Remove existing roof coverings down to the boarding which shall be repaired and treated with a preservative to resist rot and insect attack and renewing any rotten or decayed timbers. Reclad with steel sheeting on new purlins with vapour control layer and insulation. Option R4 - Repair existing sheeting and coat with a waterproof compound Where a defective roof needs making good for a short term, perhaps less than five years, the existing sheeting can be cleaned, repaired and coated with a proprietary waterproof compound. Gutter repairs may also be necessary. Figure F2 illustrates how various roofing materials may be applied to the different roofing options (Sect 7.5). Figure F2 Application of roofing materials to roofing options MATERIAL OPTION 1 FLAT OVER-ROOF OPTION 2 Remove existing timber OPTION 3 MULTI-PITCH PROFILE Retain & repair existing timber OPTION 4 Retain & repair existing sheeting A Single ply membrane B Standing seam concealed-fix Aluminium sheeting C Traditional profiled steel sheeting D Traditional profiled aluminium sheeting E Composite sheeting F Fibre cement sheeting G Coat with waterproof compound The recommended solution is to adopt the flat roof options using either single ply or standing seam concealed-fix Aluminium sheeting. All the material options and roofing concepts are described and discussed below. 84 December 2001

107 Annex F Roofing options & description of roofing materials Description of roofing materials Material A: Single ply membrane The single ply membrane can be laid at minimal falls and is also suitable for pitched roofs. It is laid over rigid insulation board and fixed to an underlying profiled structural liner sheet spanning across the purlins. A separation fleece may be required to physically isolate the membrane from what may be chemically incompatible insulation board. Insulation boarding must be sufficiently robust to allow foot traffic for maintenance access and this trafficking must be designed for. In addition, a vapour control layer is normally provided beneath the insulation to prevent migration of water vapour. Otherwise such vapour can condense on the underside of the cooler membrane and be retained by the insulation which should be kept dry. The resulting local dampness reduces the effectiveness of the insulation and also may initiate corrosion of the fixings and liner. The liner sheeting should be galvanised for durability and may be suitably coated to improve brightness of the internal working environment. Mechanically attached single ply membranes are laid in rolls and secured to the substrate by either individual fixing plates placed along one edge or linear bars secured over the roof membrane. Fixings centres must be determined by the need to resist uplift load due to wind in accordance with British Standards. Adjoining rolls are overlapped, covering the fixings in edge fastened systems, and jointed by either hot air welding or chemically bonded solvent welding. Adhered roofing systems are laid in rolls secured to a suitable substrate with the manufacturers recommended adhesive. Adjoining rolls are overlapped and jointed by either hot air welding or chemically bonded solvent welding. Guarantees are available for single ply membranes. The manufacturers' recommendation and the conditions of any guarantee should be followed. A major advantage of the single ply membrane is that no fixings or sealants are exposed to the external hostile environment, and material specifications are available for good tear-resistance, durability and dimensional stability. Material B: Standing seam conceal-fix aluminium system The aluminium sheeting is supported by upstanding brackets which either sit on the purlins or on a structural liner, the latter normally being more expensive. The internal liner, spanning between the purlins, is usually non-structural as it only needs to support the insulation, which has no requirement to take foot traffic and so need not be rigid. As with material A, a vapour control layer should be provided between the liner and the insulation. The liner sheeting is either in aluminium or galvanised steel and again as with material A, its underside may be colour-coated to improve the internal lighting aspect. Aluminium has a coefficient of thermal expansion twice that of steel so care is necessary in design and installation to ensure that there is adequate provision for thermal movement of aluminium sheets. In addition, if using stainless steel fixings with aluminium sheets on steel purlins, care is needed to build in precautions against bimetallic corrosion. Isolation tapes and washers should be used where necessary, making use of manufacturers' recommendations. The upstanding brackets, fixed through the liner, are placed on each purlin at centres to suit the width of the standing seam sheets. Sheets are laid in sequence with one edge of each sheet overlapping the edge of an adjacent sheet, and are then mechanically crimped together. December

108 Annex F Roofing options & description of roofing materials Aluminium sheeting may be coated for cosmetic purposes, corrosion protection is not required. Aluminium is not as hard as steel and so is susceptible to local damage and within limits this is not serious. Aluminium is still harder than the protective coatings applied to steel, and when scratched, the oxidation process is of a self-protective nature, unlike steel. Although the coating of aluminium sheeting does not prolong its lifespan significantly, uncoated mill-finish aluminium can be highly reflective and requires coating to dull this effect. Guarantees are available for standing seam aluminium systems. Manufacturers' recommendations and the conditions of any guarantee should be followed. For option study purposes the period for repaint in years should be considered (refer to BS 5427 : Part 1 : 1996). As with material A, a major advantage of this option is that no fixings or sealants are exposed to the external hostile environment. The density of aluminium is also nearly a third that of steel and so provides a lightweight roof. This makes it easier to handle, cut and drill than steel, making installation and repair of an aluminium roof a quicker process. Because of its relatively stable nature, aluminium has good economical recycling properties. Material C: Traditional profiled steel sheeting This option is not suitable for the flat roof concept, as the recommended roof pitch is in the order of 15. The built-up roof comprises high quality organically-coated, profiled steel sheeting with loose insulation on inner liner trays, all supported by purlins. If the existing timber purlins and boarding are retained, spacers will be required fixed through the boarding into the timber purlins beneath, but insulation would be supported by the boarding in lieu of liner trays. The coating is necessary to protect the steel from corroding which is likely to be initiated by damage. The steel sheet should be pre-galvanised and it is then essential that a good quality "organic" coating is specified to both the top and underside of the steel sheet. A newly installed steel roof cannot be assumed to be damage-free, due to possible careless workmanship "building-in" potential corrosion from day one. The deliberate cutting and drilling needed to fix the roof sheets and accidental damage requires additional protective treatment of the exposed steel. This slows the fixing process down but unless all exposed steel is effectively treated rusting arises. Aluminium does not require the same attention to detail. The durability of steel sheeted built-up roofs depends heavily on the quality of workmanship and exposure to the weather during installation. Any moisture or rain ingressing the insulation is rarely removed before completion. The resulting local dampness and possible saturated insulation material reduces the effectiveness of the insulation material and creates an ideal environment to initiate corrosion of the fixings, the liner and the underside of the steel sheet. The durability of the roof is also dependent on the components making up the roof system. The fixings, sealants and cut edges of sheets are usually the elements that deteriorate first and it is these that determine its useful life. Stainless steel fixings are electrochemically not compatible with steel, therefore, fixings for steel roofs are normally galvanised or sheradised but are still less durable than stainless steel. Stainless steel fixings are closer in compatibility with aluminium sheeting. Periodic repair of components such as sealants is not practical or cost-effective. Guarantees are available for coated steel sheeting. Manufacturer s recommendations and the condition of any guarantee should be followed. Steel sheeting is particularly prone to corrosion resulting from damage, installation defects, unseen damage, or by not following the manufacturers' recommendations. For option study purposes, for the functional life period and the external environment, the period for repaint should be considered, (refer to BS 5427 : Part 1 : 1996). 86 December 2001

109 Annex F Roofing options & description of roofing materials Coated steel roofing needs to be inspected annually to check for damage or at other defined periods specified under warranty/guarantee. Due to their susceptibility to corrosion resulting from damage to the coating, it is important that inspections are carried out regularly. The underlying steel is prone to rapid corrosion if damage is left undetected. Material D: Traditional profiled aluminium sheeting The make up of this roof system is similar to material C, except that the sheeting is in aluminium. It is a built-up roof comprising profiled aluminium sheeting with loose insulation on inner liner trays, all supported by new purlins. Again, the existing timber purlins and boarding may be retained, and the option is not suitable for the flat roof concept because of the nature of the system and the need for sealants. The minimum recommended roof pitch is typically 15. Aluminium sheeting is expensive initially, however, it is more durable and requires less maintenance, and is said to be more cost effective in the long term. Aluminium is not prone to corrosion and damage tends to self-heal. Coatings are required for cosmetic reasons only. Advantages referred to for standing seam aluminium also apply here, except that the durability of the whole system also relies on the fixings and sealants used. Care is needed in specifying ancillary components, to ensure the envisaged lifespan applies to all parts of the system. Periodic repair of components such as sealants is not practical or cost-effective. Material E: Composite sheeting Composite sheeting comprises a series of pre-assembled panels bonding two profiled metal skins around a core of insulation in a sandwich construction. The sheeting can be in either coated steel or aluminium. Although normally more expensive initially, the system usually provides a better quality product than the equivalent built-up system. As the internal and external sheets are separated by the insulation, cold bridging is minimal, which reduces the risk of soffit condensation. Factory assembly gives scope for better quality control measures hence the risk of water ingress to the insulation is reduced. The drawbacks are that the multi-pitch nature of the Type C roof dictates short lengths of cut panel. The system still requires sealants and fixings along the joints and, because of its composite nature, damage is both more expensive to repair. Treatment of steel panel cut edges is still needed, and regular inspections are required to ensure the continued effectiveness of the coating is maintained. Composite panels are heavier and more difficult to handle, and their rigidity also offers little flexibility to accommodate irregularities found in old roof structures. The system is unsuitable for the flat roof concept due to the minimum roof pitch requirements associated with the flat roof. The expected lifespan depends on the materials used. December

110 Annex F Roofing options & description of roofing materials Material F: Fibre cement sheeting This option is a similar system to the original asbestos cement roof sheeting, in terms of appearance. The ability of the sheeting to resist bending, relies on the tensile performance of the fibres. Although the fibres have an adequate tensile yield stress, they stretch excessively under load and the cement cracks. When laid on Type C roofs, fibrecement sheeting, therefore, has limited capability to accommodate irregularities found in the roof structure and any movements. This material has good breathability and reduces condensation. Additional insulation should be provided for which existing timber boarding or new liner trays and purlins would be needed to support the insulation if placed within the new roof construction. Material G: Coat with waterproof compound Where a defective roof needs making good for a short term of less than five years, a proprietary overlay or patch repair system may be considered. The existing sheeting requires thorough prior cleaning. Provision should be made for the collection, retention and disposal of any asbestos fibres loosened in the cleaning process. Proprietary cleaning systems are available, which use special brushes pre-cut to the profile of the existing roof. The existing roof needs a thorough check for integrity of fixings, cracked sheets or evidence of leaking. Repairs are required before the cleaning proceeds. After cleaning, a fungicidal wash is required to kill off and remove lichen spores embedded in the roof surface. After completing all preparation work, a quality waterproof and vapourpermeable coating may be applied to the existing sheets. Other materials Lead, copper, zinc or slate roofing materials are available, however it is not considered that these materials are appropriate for the large areas involved. Period to repaint For option study purposes, the period to repaint in years should be considered within the context of the type of external environment, and the guidance given within Annex D, of BS:5427:Part 1:1996. GUIDANCE PUBLICATIONS BS 5427:Code of Practice for the Use of Profiled Sheet for Roof and Wall Cladding on Buildings. Part 1:Design Profiled Sheet Roofing and Cladding : A Guide to Good Practice, National Federation of Roofing Contractors. Third Edition:1999 Technical Paper No 5:Metal Wall Cladding Detailing Guide, MCRMA Technical Paper No 6:Profiled Metal Roofing Design Guide, MCRMA Technical Paper No 9:Composite Roof and Wall Design Guide, MCRMA BRE Digest 372:Flat Roof Design: Waterproof Membranes, BRE CIRIA Book 15:Flat Roofing Design and Good Practice, CIRIA The Single Ply Roofing Association - Code of Practice Guidance of Design Criteria For Single Ply Roofing Membranes Durability of Cladding:A State of the Art Report, W S Atkins & Others Coated Metal Roofing & Cladding:Oliver Albon & Garner, Thomas Telford Ltd. 88 December 2001

111 Annex G Window refurbishment options and typical window drawings The advantages and disadvantages of the various window options (sect 9) are: OPTION ADVANTAGES DISADVANTAGES COMMENT OPTION W1 Remove existing and provide solid infill, or overclad with suitable insulated opaque cladding. Savings in heat losses. Full artificial lighting is normally required for winter or night working. Removes natural light provision, and is therefore not appropriate when natural light is specifically identified in the statement of requirement. Practical and economical, particularly in the long term. DE RECOMMENDED OPTION OPTION W2 Remove existing and replace with translucent wall cladding or multiwall polycarbonate sheeting with suitable light diffusion, thermal and durability characteristics. Diffusive properties of translucent cladding or polycarbonate sheeting provide improved lighting conditions, more suitable to the working environment required in hangar type buildings. Sympathises with the preferred solution to overclad the walls, and translucent sheeting can be in the same profile as the main wall cladding. Additional costs of window provision. Practical and economical solution when the SOR dictates natural lighting. OPTION W3 Remove existing window and replace with double glazed units in appearance similar to existing. Improved appearance. Expensive initially. Diffused glass removes clear views. Hangar type buildings do not need high specification double glazed windows, which are more suited to office buildings. OPTION W4 Retain existing windows if condition permits, and repair. Strengthen if required. Full repair costs may not be apparent until work starts. Maintenance is high. Corrosion accelerated by the condensation problems. May be a need to strengthen the windows. Heat losses are not reduced. Diffused and contrasting patterns of light with varying intensity is not ideal for hangar-type work. Frames are usually corroded, particularly the bottom cill. December

112 Annex G Window refurbishment options and typical window drawings Typical drawings are given to illustrate the typical solutions. However, it shall remain the responsibility of the contractor to provide as constructed solutions which are fit for purpose. Window head Flashing Continuous 90x90x8 ms galv. angle bolted to top of window. Clear triple wall polycarbonate sheeting fixed in accordance with the manufacturer's instructions. Sheradized steel fixings. 90x90x8 ms galv. angle bolted to vertical members. Continuous 90x90x8 ms galv. angle bolted to bottom of window. Option W2 - Vertical section thro' window showing New Polycarbonate Sheeting VERTICAL SECTION 89x89 rsj (min) or 2/90x90 ms angles at expansion joints. Actual sizes of vertical supports to suit height of windows and hangar location. Option W2 - Horizontal section thro' window showing New Polycarbonate Sheeting HORIZONTAL SECTION Manufacturer's end plate 90x90x8 galvanised ms angles 90 December 2001

113 Annex G Window refurbishment options and typical window drawings Option W2 - Vertical section through window showing new translucent sheeting December

114 Annex G Window refurbishment options and typical window drawings Option W4 Vertical section showing strengthening of existing Profilit glazing 92

115 Annex H Door refurbishment options Any option should have regard to the extant information. TB99/29 Safety of Structure - Recommendations for users during adverse weather conditions. TB99/30 Inspection, maintenance, adjustment and use of large sliding and folding doors. TB99/31 Guidance on works during hangar refurbishment and hangar identification. TB97/40 H&S - Fixed electrical power distribution for aircraft hangars and hardened aircraft shelters. HSWN 01/02 Inspection of hangar doors, Door Top Guides - Type C hangars. HSWN 95/07 Inspection of hangar doors. The options below draw out some of the issues involved. A detailed site specific analysis is required at each site. December

116 Annex H Door refurbishment options OPTION ADVANTAGES DISADVANTAGES COMMENT OPTION D1 Refurbish existing doors. A. Manual operation Operation of doors will be greatly improved due to: - Reduced weight; - New running gear; - Manual brake; - Continuous and adjustable bottom track; - Removal of general debris via catchpits to prevent jamming; - Removal of surface water via catchpits to reduce incidence of ice formation. Reliance on manual operation. Braking and crank handle "snatching" significantly reduced but not entirely eliminated. Full maintenance access to all running and operating gear. Maximum number of open door configurations maintained. Maximum door width and height maintained. Maximum flexibility for future use maintained. Heat loss minimised. Lowest cost of all options. Minimal running costs. Reduced maintenance costs. B. Automatic operation Operation of doors will be greatly improved (as Option D1A) Full electric operation with manual override provided. Maximum door height and width maintained. Flexibility for future use maintained. Heat loss reduced. Reduced maintenance costs. Initial cost is prohibitive when compared with option D1A. Maintenance costs are likely to be higher than option D2 where totally new doors are provided. Current operational flexibility in terms of open door configurations reduced due to door linkage. In order for this option to achieve the same low level of maintenance as option D2 a high emphasis will be required when assessing the acceptability for re-use or otherwise of the existing door components. Good compatibility will need to be achieved between existing and new components to ensure that all elements achieve the required operational design life. OPTION D2 Provide new doors similar to existing with automatic operation All door components are new. Ease of operation. Full maintenance access to all running and operating gear. Maximum door width and height maintained. Heat loss minimised. Maintenance costs are likely to be less than option D1B. Increased certainty of achieving required minimum design life when compared to Option D1B. Highest initial cost. Potential for icing-up of bottom tracks remains. OPTION D3 Do nothing 1) long term risks to H&S of operatives and damage to equipment due to collapse of doors 2) ever increasing maintenance costs. 3) increased risk of disruption to hangar operations Not recommended. 94

117 Annex H Door refurbishment options OPTION ADVANTAGES DISADVANTAGES COMMENT OPTION D4 Decommission but retain as a structural wall Maintenance of doors and running gear reduced. Heat loss minimised. Low cost option. Insulation linings can be fixed to the inside face. Re - Commissioning will be very difficult, and full inspection will be required. Doors must be in good structural conditions. OPTION D5 Remove existing doors and infill End walls can be fully insulated. No external maintenance. Existing good condition doors can be used on other structures. High initial costs. Not readily amended back to full hangar doors. OPTION D6 Remove existing door, infill partially and provide reduced height and/or width doors Lowest initial cost for electrically operated doors. Lower maintenance costs than some options Ease of operation Icing-up of bottom tracks can be eliminated. Addresses all Health and Safety issues attached to manual operation. Least heat loss of all options. Door openings optimised for use by vehicles, helicopters etc. Minor reduction in flexibility for future use by larger aircraft. This option will preclude the use of the hangars aircraft as identified as being too wide or too tall. Reduction in long term flexibility. To lessen the effect of any long term loss of flexibility, it would be prudent to retain the top guides and outrigger frames under this option. This would permit future re-installation of doors with the maximum clear opening if required. Note: The methodology given is illustrative of the items which may be required. This is given as an indication of the requirement. Each site will require a specific design. December

118 Annex H Door refurbishment options 96 December 2001

119 Annex I Cost comparisons No option for a solution can be given full consideration without some idea of cost implications. Technical solutions on their own do not carry any merit unless they can be proved to be economically viable. Budget cost estimates are, therefore, given in this chapter for the basic work items in connection with a typical Type C hangar, roof refurbishment. All costs are base estimates, in that they are raw costs without inclusion of risk additions, preliminaries, VAT or professional fees. A site specific investment appraisal of the various options should take all such factors into account. All estimates will require validation for a particular project and updating to current price levels. They provide a rough guide for budgeting and comparison purposes. If for security reasons a dado wall is built around the perimeter of the building, then extra over costs will be incurred. The costs for a new build hangar are not provided. It is unlikely that the Project Sponsor s requirement would be for the same footprint or height of hangar. Experience indicates that a rigorous approach to determination of space requirement dictates a smaller structure with commensurate lower costs. For comparison purposes within the Option Study it will, therefore, be necessary to obtain a Statement of Requirement which provides the space requirement. If a green field site is chosen, the cost of site preparation and laying new services will need to be included, together with provision of a ground slab. The costs for refurbishment are less than a new build hangar of the same size. However, a new hangar can be designed to present day operational needs, normally with reduced maintenance and running costs. Whole life costs of the different options should be taken into account in an investment appraisal. The DE view is that refurbished Type C hangars represent the best option for the client, subject to their being a defined need for the extant hangarage space. December

120 Annex I Cost comparisons COST ESTIMATES FOR ROOF REFURBISHMENT TYPE C 1938 Based on estimates at the first quarter 2000 prices OPTIO N R1 R2 R3 R4 DESCRIPTION Provide new mansard over roof, remove existing roof covering including timber boarding VARIANT A Clad with single ply membrane ITEM COST Strip Work to existing New roof construction New parapet gutters Total Option R1A RECOMMENDED OPTION B Clad with aluminium standing seam Strip Work to existing New roof construction New parapet gutters Total Option R1B Retain existing valley profile, remove existing roof covering including timber boarding Retain existing valley profile, remove existing roof covering, retain and repair timber boarding Repair and coat original sheeting with a waterproof compound A Clad with profiled steel sheeting B - Clad with profiled aluminium sheeting C Clad with composite steel sheeting A Clad with profiled steel sheeting B Clad with profiled aluminium sheeting Strip Work to existing 8360 New roof construction New valley/parapet gutters Total Option R2A Strip Work to existing 8360 New roof construction New valley/parapet gutters Total Option R2B Strip Work to existing 8360 New roof construction New valley/parapet gutters Total Option R2C Strip Work to existing New roof construction New valley/parapet gutters Total Option R3A Strip Work to existing New roof construction New valley/parapet gutters Total Option R3B Not recommended. Poor value for money Total Option R4 Approx Note: The above figures are subject to confirmation and are based on a C Type hangar with 12 bays giving a footprint of 4180 m 2 on PLAN (excluding annex roofs). 98 December 2001

121 References 1. Appraisal of Existing Structures, 2nd Edition, The Institution of Structural Engineers. 2. Appraisal of Existing Iron and Steel Structures, Publication 138, Steel Construction Institute. ISBN Assessing the Capacity of Existing Steelwork, Paper AD135, New Steel Construction, Vol 1, No 4, June Steel Construction Institute. 4. Historical Structural Steelwork Handbook, Publication No 11/84, The British Constructional Steelwork Association Ltd. ISBN BS 15: Standard Specification for Structural Steel for Bridges and General Building Construction. 6. BS 449: Use of Structural Steelwork in Buildings. 7. BS 449: Use of Structural Steelwork in Buildings. 8. BS 5427: Part 1:1996. Code of Practice for the Use of Profiled Sheet for Roof and Wall Cladding on Buildings. British Standards Institution. 9. BS 5628: Part 1: Code of Practice for Use of Masonry. British Standards Institution. 10. BS 5950: Part 1: Structural Use of Steelwork in Building. Code of Practice for design. Rolled and Welded Sections. British Standards Institution. 11. BS 6399: Part 1: Loading for Buildings - Code of Practice for Dead and Imposed Loads. British Standards Institution. 12. BS 6399: Part 2: Loading for Buildings - Code of Practice for Wind Loads. British Standards Institution. ISBN BS 6399: Part 3: Loading for Buildings - Code of Practice for Imposed Roof Loads. British Standards Institution. ISBN BS 6651 : Code of Practice for Protection of Structures Against Lightning. British Standards Institutions. 15. BS 7543 : Guide to Durability of Buildings and Building Elements, Products and Components. British Standards Institutions. 16. BS CP 3: Chapter V: Part 2: Code of Basic data for the Design of Buildings - Wind Loads. British Standards Institution. ISBN BS EN 12056: Parts 1 to 5: Gravity Drainage Systems Inside Buildings. British Standards Institution. 18. BRE Report 254: Repair and Maintenance of Reinforced Concrete. Building Research Establishment. ISBN December

122 References 19. BRE Report 262: Thermal Insulation - Avoiding Risks. Building Research Establishment. ISBN BRE Digest 346: The Assessment of Wind Loads, Parts 1 to 9. Building Research Establishment. 21. BRE Digest 372: Flat Roof Design. Waterproof Membranes. Building Research Establishment. ISBN BRE Digest 444: 3 Parts: Corrosion of Steel in Concrete. Building Research Establishment. 23. BRE Information Paper 19/81: Assessment of Hard Body Impact Resistance of External Walls. Building Research Establishment. 24. Technical Instruction CE: 104: Appraisal of Existing and Design of New Runway and Lifting Beams. Property Services Agency. 25. Corrosion Damaged Concrete: Assessment and Repair: By Pullar-Strecker, P Butterworths. ISBN Health and Safety at Work, etc, Act: HMSO. ISBN The Workplace (Health, Safety and Welfare) Regulations: Statutory Instrument No HMSO. ISBN The Management of Health and Safety at Work Regulations: Statutory Instrument No HMSO. ISBN The Construction (Health, Safety and Welfare) Regulations: Statutory Instrument No HMSO. ISBN Health and Safety (Guidance) HSG 33: Health and Safety in Roof Work. HSE. ISBN Health and Safety (Guidance) HSG 150: Health and Safety in Construction. HSE. ISBN The Provision and Use of Work Equipment Regulations: Statutory Instrument No HMSO. ISBN Manual Handling Operations Regulations: Statutory Instrument No HMSO. ISBN Health and Safety (Safety Signs and Signals) Regulations: Statutory Instrument No 341. HMSO. ISBN X. 35. Construction (Design and Management) Regulations: 1994 (as amended by the Construction (Design and Management) Amended Regulations 2000) Statutory Instrument No HMSO. ISBN Control of Substances Hazardous to Health (COSHH) Regulations: Statutory Instrument No 437. HMSO. ISBN The Building Regulations: 2000 Statutory Instrument No HMSO. ISBN The Building Standards (Scotland) Regulations: Statutory Instrument No HMSO. ISBN December 2001

123 References 39. The Building Regulations (Northern Ireland): Statutory Rule No 243. HMSO. ISBN Environmental Protection Act: HMSO. ISBN Crown Fire Standards: Crown Fire Standard: D6. July Fire Alarm Systems - Automatically Operated. Crown Fire Standard: E4. July Office Buildings. Crown Fire Standard: E9. July Vehicle Workshops and Storage, Garages and Car Parks. Crown Fire Standard: E10. July Aircraft Hangars. Crown Fire Standard: E11. July Storage Premises. 42. Department of the Environment: Standard Fire Precautions for Contractors Engaged on Crown works. HMSO. ISBN Defence Estates. Property Management of the Defence Estate - DEO(W) Specification 005 Issue 003, Incorporating Amendment 1, dated 31/10/ Joint Services Publication rd Edition: Services Accommodation Code. Ministry of Defence. 45. Joint Services Publication 318A. 2nd Edition: Military Air Traffic Services. (Chapter 23). Ministry of Defence. 46. Joint Services Publication rd Edition: MOD Health and Safety Handbook. Ministry of Defence. 47. Joint Services Publication 418: Environmental Manual. Ministry of Defence. 48. Joint Services Publication 440. Volumes 1, 2 and 3. Defence Manual of Security. Ministry of Defence. 49. Joint Services Publication 455: Military Aerodromes Construction and Safeguarding Criteria. Ministry of Defence. 50. DEO(W) Specification 033: Pavement Quality Concrete for Airfields. TSO. ISBN DEO(W) Specification 035: Concrete Block Paving for Airfields. TSO. ISBN DWS Functional Standard 06: Guide to Airfield Pavement Maintenance. HMSO. ISBN X. 53. Design and Maintenance Guide 02: Glazing Standards for MOD Buildings Subject to Terrorist Threat. Defence Estates. 54. Design and Maintenance Guide 13: Mechanical Transport Facilities. Defence Estates. HMSO. ISBN Design and Maintenance Guide 20: The Heating of Large Spaces. Defence Estates. HMSO. ISBN December

124 References 56. Technical Bulletin 97/40: Health and Safety - Fixed Electrical Power Distribution for Aircraft Hangars and Hardened Aircraft Shelters. Defence Estates. 57. Technical Bulletin 95/23: Health and Safety CDM Regulations 1994 as Applied to Projects. Defence Estates. 58. Technical Bulletin 95/24: Health and Safety CDM Regulations 1994 as Applied to Property Management. Defence Estates. 59. Technical Bulletin 95/24; Addendum to Technical Bulletin 95/24. Defence Estates. 60. Technical Bulletin 99/29: Safety of Structure - Recommendations for Users During Adverse Weather Conditions. Defence Estates. 61. Technical Bulletin 99/30: Hangars and Industrial Buildings - Inspection, Maintenance, Adjustment and Use of Large Sliding and Folding Doors. Defence Estates. 62. Technical Bulletin 99/31: Hangars - Guidance on Works during Hangar Refurbishment. Defence Estates. 63. Technical Bulletin 00/06: Fixed Access Ladder Systems. Defence Estates. 64. Technical Bulletin 01/26: The Method of Operation of the MOD Building Control Compliance System. Defence Estates. 65. Health and Safety Warning Notice 95/07: Inspection of Hangar Doors. Defence Estates. 66. Health and Safety Warning Notice 01/02: Inspection of Hangar Doors, Door Top Guides. Type C Hangars. Defence Estates. 67. Safety Rules and Procedures. SRP 07: Procedures for Working at Height. Defence Estates. (To be issued in due course). 68. AP 113A Earthing of Aircraft and Ground Support Equipment. Defence Estates. 69. AP 100D Precautions Against Electric Shock in Electric Hazard Areas of Electric and Electronic Facilities. Defence Estates. 70. Other Relevant AP's, (eg. AP 100B - 01). Defence Estates. 71. Various Other AGL Requirements / Standards Such as for Exterior Lighting to Hangars in Vicinity of Airfields. eg. Drawing No CU (M&E) Defence Estates. 72. Profiled Sheet Roofing and Cladding: A Guide to Good Practice: Third Edition E & FN Spon. ISBN Durability of Cladding: A State of the Art Report, WS Atkins. Thomas Telford. ISBN Coated Metal Roofing and Cladding: Oliver, Albon and Garner. Thomas Telford. ISBN X. 75. Flat Roof Design and Good Practice: Book 15. CIRIA. ISBN December 2001

125 References 76. The Single Ply Roofing Association: Code of practice. (Soon to become a British Standard). Guide on Design Criteria for Single Ply Roofing Membranes. (Under revision). Product Sheets 1 to 6. (Soon to be incorporated into design guide). Further information is available from: The Single Ply Roofing Association The Building Centre 26 Store St London WC1E 7BT Tel: Fax: The Metal Cladding and Roofing Manufacturers Association: Technical Paper No 5: Metal Wall Cladding Detailing Guide. Technical Paper No 6: Profiled Metal Roofing Design Guide. Technical Paper No 9: Composite Roof and Wall Cladding Panel Design Guide. Further information is available from: The Metal Cladding and Roofing Manufacturers Association 18 Mere Farm Road Prenton Wirral Cheshire CH43 9TT Tel: Fax: December

126 Prepared by: Wind Sensitive Structures Specialist Services December 2001 Defence Estates Blakemore Drive Sutton Coldfield West Midlands B75 7RL Tel: Fax: Sutton Coldfield Mil Extn (9) 4421