St Albans

The lower ground floor of this relatively new-built block of flats was undergoing refurbishment after flooding from a burst water tank, when some decay to the structural timber frame was noted. Further opening-up of the timber frame at and above skirting level revealed what appeared to be extensive wet rot decay to the sole plates and studs throughout the three flats on the lower ground floor level. Breaking-up of the slab and screed around the embedded internal and external wall timber sole plates uncovered severe localised decay. On inspection there was what appeared to be significant dampness left over from the flood, as well as visible liquid water from continuing plumbing leaks. Although drying methods had been implemented via the use of injection drying equipment; mould growth was evident in many places particularly on the wall surfaces. H+R were instructed in conjunction with loss adjusters to assess the extent, and likely source, of the decay to the timber framing, and to advise on cost-effective remedial works to allow the flats to return to domestic occupancy and to maintain the capital value of the building.

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Work undertaken

Due to high-quality retail finishes within the building, the investigation comprised a detailed internal and external examination of the area of timber frame in question, with targeted decay detection drilling and deep and surface moisture probing, in conjunction with borescope and videoscope technology where necessary within building voids and areas inaccessible at the time of survey. Microscopic analysis of insect frass and samples for species identification was also undertaken later in the H+R laboratory.

How we solved the problem

Structurally significant decay was detected, but generally confined to one primary corner post where wet rot decay and subsequent wood-boring beetle infestation had resulted in almost total loss of cross-section. Detailed external investigations revealed a number of remedial patches affecting the rainwater goods directly corresponding to the internal decay, which when combined with use of a bituminous impermeable lining between the timber frame and the cementitious render to the façade, was considered to have significantly exacerbated the effects of any moisture ingress. However, moisture content readings were mostly well below the decay threshold, with the majority below 12-10 per cent w/w, and as such the wet rot decay was considered historic. The extent to which the oak heartwood had been decayed by wood-boring beetle, in this case Death watch beetle (Xestobium rufovillosum), suggested chronic and frequent saturation by liquid water over a long period of time, and using this information, together with the moisture readings taken on the day, it was possible to produce a likely timeline to present to the client.

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