HODGES BARN SHIPTON MOYNE GLOS STRUCTURAL REPORT

Transcription

1 HODGES BARN SHIPTON MOYNE GLOS STRUCTURAL REPORT Date of inspection 22 May 2008 Inspection Carried out by: James G B Birdwood MA CEng MICE MIStructE Weather Dry

2 1. Introduction We were appointed by Mr & Mrs N. Hornby of Hodges Barn, Shipton Moyne to carry out an inspection and report on the structural condition of the roof of Hodges Barn. Our report is concerned only with this structural issue. All other aspects of the property are outside the scope of our report. No exposing work was carried out; our observations are based on a visual inspection. This report is prepared for the use of the above named clients only and may not be used or relied upon by any third parties without our specific written authorization. 2. General Description and Scope of Report The property is a cruciform stone barn, converted to residential use in the mid 20 th Century. The roofs are covered in Cotswold stone tiles laid in diminishing courses. There are hip ended wings to east and west with two storeys of accommodation in each. The attic of the west wing also contains one bedroom. The east wing attic is unconverted. The north and south wings comprise three storey stone towers with timber framed and stone slated domes to each. There is a second floor landing at the central crossing with a flat roof and glazed lantern above. In this report we are addressing the condition of the load bearing structures of the east and west wing hipped roofs, and of the north and south wing domes. In all four of these areas the stone tiling, though originally carried out to a high standard, is now at the stage where it needs to be stripped and relaid onto new battens or laths.

3 Our report is intended to identify those areas where repairs are needed to the rafters and principal roof timbers, and make recommendations for those repairs. We have also been asked to consider the strengthening works required to create usable floor space in the east wing attic, and to extend the floor space in the west wing. 3. External Observations East & West Wings On both wings there are signs of movement in the underlying structure, with the slopes ridged up at the main truss positions, and sagging between. This is a long standing issue caused mainly by deflection in the purlins, and is not in itself a cause of structural concern. At the NE corner there is substantial deflection in the lower hip purlin and the hip rafter, again of long standing, but the distortion in this area goes beyond what is normally acceptable. At the eaves it appears that a stone cornice has been added at the time of conversion, and a lead apron / capping has been introduced between the edge of the stone tiles and gutter. This is an unusual and potentially problematic detail as any failure of the lead can lead to soaking of the masonry walls. North and South Wings These could only be inspected from ground level. There is no evidence of underlying structural movement in the domes, and also no evidence of outwards movement in the parapets at the base of the domes.

4 4. Internal Observations East Wing This is a hipped roof structure in four bays of varying width, the east end being wider to suit the hip geometry. At the inner end there is a recent 9 brick wall dividing the attic from the central top landing. The roof structure is a mixture of oak and elm framing. There are three principal trusses consisting of Tie Beams at wall plate level, 275mm deep x mm wide. Principal Rafters typically 275 x 125mm Collars at mid height typically 150x90mm There is a principal rafter and collar at the centre of the hip, but no tie beam. There are two rows of purlins in each slope of varying size, typically between 150 and 175mm square, housed into the principals. Common rafters are typically 75mm deep x 100 mm wide. Laths and lime plaster torching are still reasonably intact above the rafters. There is no sarking felt. There are modern ceiling joists spanning between the tie beams, 100 x 50mm in the three inner bays, and 125x50 in the longer span end bay. A brick chimney has been introduced in the centre of the east end, and an ad-hoc arrangement of softwood framing has been installed to trim around it. At the south end of the central truss, the tie beam end has in the past rotted out, and an additional piece laid alongside and bolted to it. This repair is probably 19 th century in origin. Purlins are generally sound although overspanned particularly at the hip end lower purlins, where significant deflection has occurred. An additional lower purlin has been inserted in the south slope of the second bay in, supported on a face fixed timber plate. This repair is of long standing.

5 The NE hip rafter has sagged, and there is evidence of dampness at its lower end, however there was a large wasp nest nearby, and a close inspection was not attempted. Where visible the common rafters are in reasonable condition. It is to be expected however that the bottoms of the rafters, and the supporting timber plate will be affected by riot and beetle, and that some replacement will be required. There is some beetle infestation throughout the roof structure, but the structural members are not in general significantly weakened by this. There are a few signs of dampness around the edges of the roof, and there is one bucket presumably intended to catch a drip, but this was empty at the time of inspection. West Wing This wing is the same shape and size as the east wing, and with the same original structure, although it has been altered more recently. The two inner bays of the attic have been converted to a bedroom and the structure is largely concealed, although there are no signs of deficiency. The overall floor zone is about 250mm deep, suggesting that deeper floor joists have been installed, suitable for residential use. There is a studwork partition attached to the central roof truss, and the two outer bays beyond this are being used as a store. The floor level is about 125mm lower in this area, suggesting that the joists are shallower, similar to the ceiling joists in the east wing. The ceiling in the store area is clad in fibreboard, but parts of this are missing, revealing bituminous sarking felt above the rafters, and no sign of the original torching. This wing was probably re-roofed at the time of conversion. The original principal rafters, collars and purlins are visible, and similar to the east wing. The collar on the truss closest to the hip has been reinforced with an additional piece of timber and an iron strap where it has deflected sideways and split as a result of pressure from the hip end collar. These repairs are of long standing but have effectively failed.

6 The tie beams from the central and west trusses appear to have been removed at the time of conversion and replaced by a pair of 225 x 75 softwood ties, one at floor level and one about 0.75m above, joined by a central stub post. This may have been done to achieve the desired ceiling level in the bedroom below, or perhaps as a result of decay in the original timbers. The arrangement is satisfactory at present but would of course have to change to give a level floor through the whole space. North Wing The dome structure is of oak or elm framing consisting of 16 principal curved ribs, equally spaced. The ribs taper from 175 deep by 65 wide at the base to about 100mm x 75mm at the top. The ribs are supported on a sectional curved timber plate (or ring beam) 175mm wide x 125mm deep. This sits directly on the walls forming the rectangular tower, and spans across the corners. At the top of the dome there is a circular oculus framed by a timber ring at which the principal ribs abut. Between the principal ribs there are two secondary ribs each 175 x 50mm, curved and tapered in the same way, and spanning onto trimmers between the principals near the top of the dome. Laths and lime torching are still reasonably intact above the ribs, and there is no felt. There is an arrangement of diagonal ties, binders and a platform below the central oculus. The purpose of these timbers is not clear, but they do not seem to be part of the original dome construction. The undersides of the ribs show that the internal surface of the dome has never been plastered. In the walls below the ring beam the nesting holes of the dovecot are still to be seen. There are joists forming the ceiling of the bedroom below and supporting a galvanized water tank, but these are quite separate from the roof structure.

7 There is evidence of leaking around the base of the dome, and some sections of the timber ring beam are very worm eaten, as are the bottom ends of some of the ribs. These defects can be dealt with by local repair and piecing in of new timber. The re-tiling of the dome will be a specialist operation, in particular the fixing of new curved laths or battens, and the careful numbering and selection of the tapered stone tiles. Expert advice should also be taken on the feasibility of using a sarking felt in this situation. South Wing The construction of this dome is identical to the North wing, but there are no intermediate ties binders or platforms. It is however apparent that the underside of the dome was plastered in the past, as nails and traces of lime remain. There is also a decorative rose (or vent) under the oculus, and a painted timber cornice at ring beam level. This suggests that there was a room under the dome, either part of a dwelling or an office, and not just part of a barn. The condition of this dome was less visible mainly due to the cornice, but it appears similar to the north wing. Central Area We did not have access to this part of the roof, but there is no evidence internally of structural inadequacy.

8 5. Comments & Conclusions During the course of re-roofing the building it will be necessary to carry out repairs to damaged timbers, and to replace a proportion of rafter ends and wall plates that have been affected by decay or infestation. In this regard the roof structure is in a typical condition considering the age of the house and the time that has elapsed since the roof was last slated. Repairs and replacement of sections of defective timber will generally be of a localised nature, and the overall stability of the roof structure is not at risk. There are some issues highlighted in the observations above, in particular the splicing of the central truss tie beam in the east wing, and the excessive purlin deflections also in this wing, which will require specific repairs. Regarding the proposed alterations in the east and west wings, these will necessitate strengthening of the floor beams, new floor joists, raising of the truss collars and additional work in the west wing to remove the raised ties. This will require detailed drawings and design, but sketches are attached to this report illustrating the likely structural solutions. We will be pleased to answer any questions on this report. James Birdwood MA CEng MICE MIStructE

9 Hodges Barn Photographs South East Corner North East Corner

10 Sagging in North East Hip East Wing Attic

11 Splice to Tie Beam in East Wing Attic Spliced Tie Beam Junction with Principal Rafter

12 Collar Junction in East Wing Attic Collar Junction in West Wing Attic

13 Internal Structure of North Dome North Dome Ring Beam and Wall

14 Woodworm Damage to North Dome Ring Beam North Dome Ring Beam from Below

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