 St John's Church, Kates Hill, Surveys and Listing | sitemap | log in
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TIMBER DECAY SURVEY, JANUARY 2008Ridout Associates, 147A, Worcester Road, Hagley, West Midlands, DY9 0NW A timber decay survey of St John's Church, Dudley 1.0 INTRODUCTION Following written instructions from Stephen Sedwell of Astam GBC Consultancy, we visited St John's Church on Friday 4th January 2008 to carry out a timber decay survey of all accessible major timber structural elements. Internally, accessibility was a limiting factor throughout the survey with some areas being completely inacccessible (the tower) and some sections being only partially accessible (the central section of the nave roof being out of reach of the scaffold tower). Externally the S aisle and vestry eaves were reached by ladder. Our insurers require us to state that we have not inspected woodwork that is covered, unexposed or inaccessible and we are therefore unable to report on the condition of any such woodwork. Nevertheless based on our inspection of the uncovered, exposed and accessible areas, the following is our opinion. 2.0 BACKGROUND We were supplied with two documents prior to the survey. A structural survey carried out in 1993 by Ascough & Associates (following the 1992 Quinquennial), and the 2002 quinquennial. We understand the 2002 survey (that consequently misquoted the 1993 Ascough survey) formed the basis for the decision by the Diocese of Worcester to close the church on the grounds of its duty of care to the congregation and its employees. English Heritage have objected to an application by the Diocese of Worcester to make this church redundant on the grounds that the two surveys referred to above were 'too cautious'. 3.0 SURVEY The survey is in the form of a schedule of observations that has been referenced to the timber layout diagram of the church at the end of the report. An observation is followed by a relevant action in bold type should it be required. All timber was foudn to be good quality slow grown softwood. Any required replacement or resupport timber should be carried out in accordance with the timber replacement guidelines. (section 5.0). 3.1 Roof construction and Balconies Internally we were able to reach the wall plate of the W and E ends of the nave, but built in pews resrticted construction of the scaffold in the central section. We used a decay detected micro drill to test the integrity of the bearings of the N aisle tie-beams below the eaves. This instrument pushes a 1mm diameter steel probe into the timber at constant pressure. Resistance to pressure, correlating with timber density, is recorded on a revolving chart. The results are tabulated below and referenced to the diagram at the end of the report. (Copies of the chart can be provided on request). The S aisle eaves had been completely rebuilt in (we believe) 1992 and the tie beam bearings were not micro drilled. The wall head had been reconstructed around the tie beams which had been wrapped in damp proof membrane. The ends of all the common rafters had been cut off with new sections fixed to the ends, (see photograph 1 below) Photograph 1 - taken through hole made by removing sarking board between points 4 and 5 on the diagram below looking at E. This shows the ceiling void, resupported and wrapped common rafter ends and also what appear to be metal brackets supporting the upper wall plate, (circled). Photographs not included in website at present but can be seen at any of our public meetings 1. Original tie beam wrapped in DPM where Thermalite block wall head surrounds it. Tie beam notched over lower wall plate. Holes drilled in bearing indicate over zealous strength testing. All timber appears to be dry. 2. Original tie beam end cut off, new section spliced in and supported by metal plate. All timber sound and dry. 3. As 2 above. 4. 5 and 6 all as point 1 above.
13. Post and base of arched brace decayed by (what appears to be historic) brown ro. We were unable to get close to the element. (See photograph 2 below). Resupport base of post and arched brace. Photograph 2 - Base of post and arched brace decayed by historic brown rot Photographs not included in website at present but can be seen at any of our public meetings 14. Foot of nave roof principal rafter and wall plate sound. 15. Foot of nave roof principal rafter and wall plate sound 16. Foot of nave roof principal decayed by historic brown rot. After micro drilling, decay found to end at 900mm from wall plate, (see photograph 3 below). Resupport end 900mm of principal rafter. Photograph 3 - Decay to bottom 900mm of principal rafter foot in nave roof Photographs not included in website at present but can be seen at any of our public meetings 17. Base of principal rafter foot out of reach but appears to be decayed in a similar way to point 16 above, (see photograph 4 below). Resupport principal rafter foot. 18. Water staining of sarking boards indicating past water ingress. Not able to confirm if water ingress is current. 19. Foot of nave roof principal rafter and wall plate sound. 20.All truss bearings in chancel found to be sound and dense. 21. Purlin bearing decayed. Resupport. Photograph 4 - Historic brown rot decay to foot of principal rafter Photographs not included in website at present but can be seen at any of our public meetings 22. Common rafter adjacent to wall found to be decayed after hardboard lining removed. High levels of damp indicate the problem is ongoing. Replace. 23. 500mm of wall plate decayed by wet rot. Replace. 24. Floor joists and common rafters bear into pockets in the masonry. They must all be checked for decay when exposure/stripping out allows. Resupport as necessary. 25. Signs of past remedial works. Decay resulted from roof defects in a vulnerable detail above. Unclear if water penetration persists. 26. Small area of roof tiles were removed exposing the wall plate and thermalite block remedial work. The roof covering and tiling patterns appeared to be generally in good condition. The felt had torn at this point and it is unclear whetherthis was carried out as part of the exposure or if it was already in this condition. One tile had slipped from the nave and damaged some tiles on the aisle. The eaves gutter, although needing a clean out, was not as obstructed as one might have thought. (see photograph 5 below). Photograph 5 - S. Aisle roof covering and eaves in generally good condition Photographs not included in website at present but can be seen at any of our public meetings 27. A similar small area of the eaves was exposed at the E end of the S aisle. Again all the roofing elements appeared in relatively good condition. 28. The bearings of the three W-E beams supporting the roof construction above the N stairs to the balcony and tower are sound. we were unable to make an inspection of the roof covering. 29. A majority of the 6 bearings of the three W-E beams supporting the roof construction above the S stairs to the balcony and tower are decayed. Consequently the roof will require replacement. 30. The condition of the underside of the first floor of the tower (visible from the top of the stairs described in points 28 and 29), indicated the possibility of some decay to the joists that were obscured by the remaining lath and plaster. The tower was therefore not surveyed. 3.1.1 Additional Exposure A portion of the replacement sarking board was removed betwen the tie beams (points 4 and 5), to allow inspection of both upper and lower plates and the ceiling void. The eaves detail was dry. The ceiling void does have some detritus from the reroofing lying on the ceiling between the rafters. A floorboard, presumably decayed by the same building defect that allowed the tie beams to become decayed above, (point 11) was removed to check the timber of the balcony construction. The support joist (running parallel to the external wall) showed no signs of decay. 3.2 Ground floor and cellar The central nave section of the ground floor is solid and the two aisles and W section of the chancel are suspended. There is no sign of decay on the upper surface of the aisle floors or to any of the pews. A small hatch in the W end of the S aisle allowed access beneath the floor. The floor structure was supported by brick arches and vaulting. The hight of the floor void measured below 1 metre in the SW corner to over 2 metres in the NE corner, (see photograph 6 below). Photograph 6 - Vaulting below E end of S aisle Photographs not included in website at present but can be seen at any of our public meetings The floor construction has been very well designed. None of the main floor beams penetrate the external wall, but sit on a ledge built around the internal perimeter of the church. The level of the ground is roughly 150mm above the external ground and there are some points where water can be seen penetrating the fabric of the subterranean walls on the N side. This is due in main to cracked concrete slabs around the external wall bases that collect and channel surface and roof water towards rather than away from the church. However the construction means that this is not detrimental to any timber part of the structure of the church. 4.0 DISCUSSION The scope of this report is to detail our findings and relate them back to the previous two surveys mentioned in the background above (section 2.0) The summary of our findings regarding the timber decay within the main roof structures is that with the exception of the two decayed principle rafter feet in the NE corner of the nave (16 and 17 on plan below), the decayed post/brace foot (13) and the decayed tie beam bearing in the N aisle (11), the roofs have survived remarkably well considering the level of neglect over the past 5 years. The smaller roofs over the W balcony stairs and the vestry appear to have some decay issues but these are small roofs constructed with easily accessible and relatively small timber elements. We were unable to make a close inspection of the external N aisle roof or the W tower. Timber associated with the ground floor and all attached timber furniture has been protected by the well designed and built vaulted floor. All the decay issues concerning roof elements have resulted from blocked downpipes and overflowing eaves gutters. It must be ensured that all roof water is effectively collected and discharged well clear of the building. Bearing the above in mind it is confusing why the church was deemed unsafe in 2002. Working backwards, the most significant reference made by the 2002 quinquennial report to the 1993 Ascough report is section 6.011 where it is stated 'Dry rot problems of the roof timber, which was reported in March 1993, may be continuing to develop undetected, further weakening the roof structure.' This is repeated in the conclusions and is one of the main reasons for declaring the church unsafe. We must assume that the 2002 surveyor did not examine any of the roof timbers and simply based his report on the 1993 Ascough survey. The 1993 Ascough report was a structural report. Two items within the report do seem doubtful. In section 5.0.14 he suggests the roof structures of collared arched braced trusses constitute untied roofs and should have tie rods added! He also mistakes the two central light bars as decorated tie rods added at a later date. Apart from this the report is quite detailed and correctly identifies the importance of the roof being water tight (section 6.0.3), and the drainage channels being kept clear (section 4.2.1). It does not however make any reference to any current decay. One can only think that his reference to 'Problems with dry rot' (section 5.0.1), is in connection with the remedial works carried out to the S aisle eaves the year before. With reference to the structural timber within this building there is no reason to deem it unsafe. It appears the only reason the church was deemed unsafe, was due to the misinterpretation of the 1993 Ascough survey by the surveyor responsible for the 2002 quinquennial. Unfortunately the last 5 years have resulted in a deterioration of the internal finishes by condensation, a previous rat infestation and the general neglect of an important church. 5.0 TIMBER REPLACEMENT GUIDELINES The following general recommendations for reinstatement works are important in preventing any further fungal activity.
REPORT ENDS
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