Case Study 2: Dry Rot in a Listed Building
A listed building in the City Centre of Newcastle run as a pub by a leading brewer was the subject of a dry rot investigation. The client was a general maintenance and building contractor used frequently by the brewery. A fruiting body had been noted by the maintenance crew emerging from the wall ceiling junction.
The original 1840 building in Grainger Town which is the largest concentration of listed buildings in the UK had been extended in the 1940’s with the construction of a peninsular extention with concrete beamed and concrete roof covered by mineral felt.
The dry rot was noted at the interface of the two buildings as noted at ceiling wall junction. An exposure exercise revealed the suspended ceiling hiding the dry rot had been caused by attaching a timber frame to the underside of a cold concrete roof above and leaking through the now semi porous roof which was no longer adequately protected by the mineral felt roof covering. This had been repaired over the years but only after significant moisture penetration to the roof and ceiling below. Condensation between the cold concrete and suspended ceiling also accelerated germination of dry rot spores – which are present in most air.
The flat roof had insufficient fall and resulting ponding to the surface was noted with blocked vertical down pipes accessed via gaps in the surrounding parapet were not discharging the water overflow. Added to this the 1840’s architect John Dobson had designed a front elevation to be free of architectural ironwork so that the parapet gutter to the front elevation of this property and next door drained into a vertical lead pipe carried at an angle through the attic of the building then embedded in a groove in the wall from front to back to exit onto the rear gutter then discharging via a short downpipe to the rear extention. Thus additional water was discharging from two large roof slopes front and rear via one downpipe to a flat roof – an d due to lack of adequate fall of the flat roof with no discharge possible from there.
The exposure work below continued and it was found that the fungal decay had spread vertically from the timber of the suspended ceiling full depth of the 50 foot room down to within 300mm of the internal first floor level affecting window frames in its path. Thus the entire wall area on three sides full width and height had to be removed. The client was anxious to avoid its tenant the loss of the approaching Christmas trade. Thus a cavity drain membrane and dry lining was chosen after first treating the exposed surfaces with boron. This work was completed within a month.
However the existence of a further dry rot outbreak had by this time been noted to the original 19840’s building. This part was of high priority to the City Conservation officers. Dry rot had affected timber window lintels to the top floor and had grown into the party wall and down to the lintels of the second floor. The parapet gutter was inspected and found to have been relined with mineral felt rather than lead.
The rough surface of this had caused dirt to collect and vegetation to grow and block the gutter causing an overflow of water down the dressed ashlar sandstone facade.
Much of the façade had eroded due to water erosion caused by lack of adequate gutters then leading to inappropriate masonry repairs in cement with resultant acceleration of erosion. The facade itself was an ashlar facing 50mm thick as originally built pinned with iron pins to the front semi dressed rough coursed stonework core of the wall. Several sections of the façade had become semi detached and during the course of the works (which had by now been put on hold by the brewery ) fell off into the street below narrowly missing the public and building’s caretaker.
The downward raked internal down pipe delivering rainwater to the rear single collection downpipe from the front roof slope was found to be blocked forcing back up of water adding to the overflow as noted above.
In the meantime the dry rot had grown into the party wall and a further outbreak due to the inadequate and overflowing roof drainage to the rear had affected the large staircase window.
The tall front window reveals were lined with field panelled architraves and window shutters which had to be repaired/replaced where affected by dry rot.
Meanwhile as the costs escalated the Brewery’s internal management system escalated the work to a new cost level requiring higher authority and a different set of engineers and advisors. The brewery estates manager was concerned to meet the Christmas trade deadline. Thus the first part of the works was completed leaving the second part to the following spring. The changeover of personnel and professional advisor saw a new architect and engineer being appointed. The conservation officers had been willing to accept the recommendations of the dry rot specialist surveyor in replacing timber lintels with steel. However the new incoming architects wished to replace like with like. It further transpired that the lintels had been replaced probably 20 years previously but the listed building file contained no record of consents for this.
The main contractor was concerned primarily with assisting the brewer in meeting targets of reoccupation by the business tenant and was in any event detached from the architect who clearly had little knowledge of dry rot and as also an interior designer drawing up new décor schemes for the refurbished building.
The conservation officers now provided with a more favourable compliance situation to them accepted the architects recommendations despite it being apparent that the fungal growth could not be removed due to penetration throughout the core of the wall thus posing a future risk and timber lintels were installed. The specialist surveyor now having to make the best provision possible recommended treatment of the timber with boron and wrapping the lintels in boron impregnated breathable none vapour barrier membrane.
Despite the main contractor being put on notice that consequently no guarantee could be provided by the specialist treatment company and evidence that the lintels had only been replaced some 20 years previously the works went ahead with all timber finishing works such as skirting and architrave being fitted prior to adequate drying out of newly replastered walls.
The total cost of treatment was £79,000 and the related joinery works and new windows plus decoration were anticipated to be a further £120,000.
Meanwhile the original outbreak of dry rot to the peninsular outrigger 1940’s building where porous concrete and interstitial condensation has caused dry rot the recommendations made by the specialist company that the mineral felt roof covering must be replaced and treatment applied to the exposed concrete was ignored and a proprietary system of floating plastic covering applied direct over timber battens screwed into the concrete roof despite dry rot growth being present there. The resulting damp void with source of nutrients for the fungus acting as a latent future risk.
Conclusion is that a specialist surveyor requires not only considerable knowledge of the elements of a structure but expertise in dealing with dry rot identifying its cause and drawing up a reliable programme of treatment also taking into account requirements of a heritage building.