Identifying basic constructions

Transcription

1 Identifying basic constructions Covered in this section: Traditional construction Non-traditional construction Modern Methods of Construction (MMC) 32

2 Traditional construction The majority of houses/bungalows and many low-rise flats in Britain are of brick or brick and block wall construction, with pitched/sloping timber roofs. Solid wall construction was common from the 1800s to Cavity wall construction was introduced as early as 1900 in some areas but predominates from 1935 to the present day. Solid walls: Pre 1850 to Cavity walls: 1935 to present. Be aware of different mixes of header and stretcher bonds that require closer inspection to determine if a cavity is present and if the cavity has been insulated retrospectively. Both the above walls are of cavity construction and both show drill holes where the cavity has been filled with injected insulation. RdSAP Convention 3.01 Where a cavity wall has been identified, enter as such irrespective of the width of the cavity. Additional information on construction types in the Ageing properties and elements and Dwelling details sections. 33

3 Non-standard construction Definitions and further sources of information Included here are all constructions other than solid or cavity brick and/or block wall construction. Essentially they include: 1. Non-traditional Houses systems built between : Metal framed Pre-cast concrete In-situ concrete Timber framed Note: Both timber frame and system built are often described as non-traditional construction but they have different energy performances and are therefore identified separately in RdSAP. 2. Modern Methods of Construction (MMC) Dwellings constructed from the mid 1990 s, whose structural parts are wholly or in part manufactured off-site or on-site by contemporary methods. It includes complete housing systems built in factories through to new, site-based technologies. Identifying non-traditional and modern methods of construction Identifying specific construction types, whether non-traditional or modern methods of construction, can prove difficult. As such if you encounter a construction type that is unfamiliar to you then you should seek further advice. BRE have published several key publications to assist surveyors in identifying construction systems: BRE Report 469 Non-traditional houses: identifying non-traditional houses in the UK (below left). BRE Report BR282 Timber frame housing : Inspection and Assessment. BRE Report BR113 Steel framed and steel clad houses: Inspection and Assessment. BRE CD ROM AP149 Non-traditional housing. A collection of 82 previously published reports and leaflets on specific types of non-traditional houses. BRE Trust FB11 Modern methods of house construction by Keith Ross (below right). REMEMBER know your limitations, if this is not your area of expertise then do not accept instructions for these types of dwellings without further specialist training. Refer to the BRE website for training courses or contact the team via energyassessor@bre.co.uk. 34

4 Designated Defective A number of specific non-traditional dwelling types have been designated defective under the 1984 Housing Defects legislation (now part XVI of the Housing Act 1985) these are listed below. Non-traditional dwellings - Designated Defective List Airey Ayrshire County Council Blackburn Orlit Boot Beaucrete Boot Pier and Panel Boswell Cornish Unit Type I Cornish Unit Type li Dorran Dyke Gregory Mac-Girling Myton Newland Orlit Type I Orlit Type II Parkinson Reema Hollow Panel Schindler Smith Stent Stonecrete Tarran Temporary Bungalow Tee Beam Ulster Cottage Underdown Unitroy Unity Type I Unity Type II Waller Wates Wessex Whitson-Fairhurst Winget Woolaway Expect these types of dwellings to be over-clad and show other signs of remedial works. Cornish Unit Type 2: semi-detached left half over-clad. 35

5 Types of non-traditional construction Metal framed Principally these comprise steel framed (or steel and cast iron based) system built dwellings. About 140,000 such dwellings have at some time or other been authorised for construction in the UK, and many different kinds of system have been used. In addition to the steel systems there were a small number of aluminium framed dwellings constructed. The majority of metal framed dwellings would have been constructed for local authorities, with many subsequently passing into private hands. Few records remain with local authorities as to their location however BRE Report BR113 Steel framed and steel clad houses: Inspection and Assessment includes a useful list of locations. Some dwellings date from the interwar period but the majority date from the post Second World War period. This reflects the need for rapid re-building after the war and to a certain extent the availability of materials and manufacturing plant no longer directed to wartime production. A common feature of many systems is that the finished dwelling was made to look as close as possible to conventionally built dwellings, with the preferred finishes either brick, imitation brick or render. Some of these disguises are nearly perfect and it takes more than a superficial examination to discover that some dwellings are indeed metal framed. On the other hand, some are immediately obvious as being of unconventional design e.g. BISF Houses. If it is not obvious that the house is metal frame then the roof space is often the easiest place to confirm the construction type. The gable or flank wall normally comprises unlined sheathed metal framing, with the separating wall of metal stud framing, lined with plasterboard. It may also be possible to see the top of external wall panels at the eaves from within the roof where loft insulation does not preclude access. Sometimes it is possible to identify construction within service cupboards where linings have not been installed. Type 3 first floor BISF Type 3 first floor Riley It is important to note that the cavities of metal clad houses should not be filled; external insulation should be used instead. Where cavities are filled there is an increased likelihood of corrosion caused by condensation. 36

6 Pre-cast concrete It is reported that around 284,000 dwellings in England have concrete panels as their predominant wall structure. The earliest being constructed during the 1920s but the majority being constructed during the 1950s and 1960s There are essentially two types of pre-cast concrete dwelling system: Panel systems Pre-cast concrete on concrete framing Panel systems These essentially involve producing flat reinforced concrete panel units in a factory and transporting them to site for assembly. The structural panels are then stacked on pre-prepared foundations to typically form room or flat sized boxes. Panels being supplied for use as walls, intermediate floors and roofs. Panels used as external walls may have the concrete textured or have an external finish such as brick, tile, paint or sheet material applied to provide an aesthetic finish. Widely used in high rise developments they were also used for low rise housing. With low rise developments it was common to use the concrete panels to create a toast rack of separating walls and to use alternative materials for the external walls to the front and rear of the property. Internally concrete panels were usually wet plastered but some will have been dry-lined. Note that there are 23 different large panel systems used in the UK to construct buildings with 4 or more storeys. Pre-cast concrete on concrete framing In a large number of cases the external appearance of the dwelling will immediately indicate that it is a pre-cast concrete system built house as the frame and panels are left exposed. However a small number of systems were rendered externally during construction. Typically the systems comprise a concrete frame with storey height infill panels. The infill panels comprise pre-cast concrete panels which span either vertically or horizontally between the concrete frame. In most cases the infill panels are slotted so that they engage with the frame. Most systems were two storey and featured pitched roofs, but there are some three storey Cornish Unit blocks and most Orlit houses had flat roofs. Cornish Unit Type 1 Cornish Unit Type 2 Be aware that different types can look almost identical note the similarities between the Cornish Unit Type 1 and Gregory houses. Gregory 37

7 In-situ concrete Cast-in-situ concrete was used extensively as an alternative to brickwork during the inter-war period. A number of different systems of cast-in-situ walling were developed with the intention of lowering costs by reducing construction time. Subsequent analysis suggests that they were in fact more expensive to build than using traditional methods. There are several basic types of cast-in-situ construction: Single leaf walls with removable formwork Single leaf walls with permanent formwork Cavity walls consisting of precast concrete slabs with cast-in-situ concrete columns Cavity walls, consisting of precast concrete slabs with a cast-in-situ concrete core Cavity walls with removable formwork The concrete mixes specified included dense and clinker aggregates largely dependent on local sources. The most prolific system was the Wimpey no-fines system of which some 300,000 dwellings were constructed between the 1940s and 1970s. No-fines concrete is a non-proprietary material used extensively in Britain for the construction of both nonloadbearing and loadbearing walls in dwellings. No-fines concrete contains no sand fraction, and often has a single size stone as sole aggregate constituent. This produces a honeycomb structure in concrete which gives it a higher thermal insulation (lower U value) than that of dense concrete. System type Number built Concrete thickness Wimpey 300,000 8", 10" or 12" SSHA 25,000 8" - 10" Unit 4,350 8" Easiform Type I 2,100 8 Corolite 700 8" Foamed slag 200 9" Lamella 183 Miller temporary bungalow 100 8" Weir " In most cases in-situ concrete house walls were constructed as a single leaf and internally were wet plaster finished. Wimpey no-fines 38

8 Timber framed These are dwellings in which the loads from upper floors and roof are carried by and transmitted to the foundations by a timber frame. The claddings are generally nonload bearing and concentrate on providing weather protection and appearance. There are essentially four types of timber frame construction: Balloon frame two storey height or eaves-height external wall panels, with studs continuous from ground floor to roof. Platform frame storey-height external wall panels which are erected upon platforms formed by the ground and upper floor construction. Post and beam a structural frame of widely spaced timber posts and beams. Planked, joisted or panelled floor and roof units span between beams, and non-load bearing infill panels span between the posts to form the external wall claddings. Volumetric box assembled from three dimensional room-sized or storey width prefabricated units (see also modern methods of construction) Between 1920 and 1944 about 8,000 timber frame dwellings were built for the UK public sector with a further 100,000 built between 1944 and Numbers increased in the private sector during the1960s and 1970s. However, timber-frame lost favour in the 1980s to conventional brick and block construction. Since the late 1990s they have made something of a come back. Systems built prior to the Second World War were mostly timber-clad and are readily recognisable as being of timber frame construction. By contrast, many post war systems, particularly those built in the 1960s and 1970s, have brick claddings and are not easily distinguishable from other types of construction of the period. Even so, in most cases there are particular features that indicate the existence of timber frame construction. The claddings used for timber frame dwellings include brickwork, tile hanging (horizontal or vertical) and rendering. These may be used singly throughout or more often across a dwelling. With brick cladding the windows tend to be set back in the reveals, and there may be small gaps or soft packing beneath the window frames, under the eaves and at the tops of verges in order to accommodate differential movement between the cladding and framing. Internally, external walls are dry-lined, usually with plasterboard nailed directly to the timber framing. However those built immediately post war were often lined internally with fibreboard, possibly fixed over timber boarding. Scotwood rendered plywood timber frame 1980s rendered block timber frame As the Domestic Energy Assessor can only carry out a non-invasive inspection of a property you are likely to be limited in how to identify a timber-frame dwelling. 39

9 The roof space is often the easiest place to confirm the construction type. The gable or flank wall normally comprises unlined sheathed timber stud framing, and the separating wall is of timber stud framing, lined with plasterboard. It may also be possible to see the top of external wall panels at the eaves from within the roof where loft insulation does not preclude access. Sometimes it is possible to identify construction within service cupboards where linings have not been installed. The lining can sometimes be distinguished from drylining to a masonry wall by tapping the lining just above a window: timber frame walls usually have timber lintels which sound less hollow than other types of lintel. RdSAP Convention 3.02 If there is a system built wall that has evidence of retro cavity fill, record as system build with internal insulation and include Addendum 1. 40

10 Modern Methods of Construction The term modern methods of construction (MMC) covers a broad range of construction types ranging from complete housing systems built in factories through to new, site-based technologies. Older terms such as system building, off-site construction, industrialised construction and modular construction are still used by many. A simple classification of modern methods by built form is: Volumetric construction Panellised systems Hybrid construction Sub-assemblies and components Site based methods of construction The first four categories are usually manufactured in a factory. The term site based methods covers systems that do not fall neatly into the first four categories. Volumetric construction This involves the production of three-dimensional units in a factory. The units are transported to site where they are stacked onto prepared foundations to form the dwellings. A typical house is made from four units, whereas flats are usually formed using two units or with smaller flats a single unit. All of the necessary internal finishes, services and, potentially, the furnishings can be installed at the factory, with the complete entity transported to site and assembled. Some external finishes can be applied in the factory (for example brick slips), but usually some work is required on site in order to make good between units. To date most volumetric construction has been used in the hotel, student and key worker accommodation, healthcare and fast food sectors, however this method of construction is now being introduced to housing. Panellised systems This involves producing flat panel units in a factory and transporting them to site for assembly. These can be constructed in a variety of materials and constructions ranging from framed panels in timber or steel, to concrete and composite panels such as SIPs (structural insulated panels). Panel systems are referred to as open or closed. Open panel systems are framing systems (metal or timber) delivered to site before insulation, services etc. are fitted. Closed panel systems are more complex and can have services, windows, doors, internal wall finishes and external claddings fitted at the factory. Hybrid construction This method of construction involves a combination of volumetric and panellised construction. Typically three dimensional volumetric units are used for the highly serviced areas such as kitchens and bathrooms with the remainder of the dwelling constructed with panels. They can include a mix of construction and material types with steel framed volumetric units and timber-frame panellised elements. 41

11 Sub-assemblies and components From the point of view MMC, this applies to innovative constructions for floors and roofs that use engineered products such as timber I beams or lattice joists, which might be installed on site as prefabricated cassettes. It does not include factory produced sub-assemblies and components such as door sets, windows, stair strings etc. which have been used in factory manufactured or traditionally built dwellings for some time. Site based methods of construction This category relates to site-based assembly methods and the use of traditional components in an innovative way. This includes Tunnelform (cast-in-situ concrete using heated steel moulds), aircrete planks and thin joint blockwork. Other innovations include the use of brick slips, insulating formwork and single leaf masonry. 42

12 in-situ concrete brick slips polystyrene permanent shuttering brick slips 43