Non-destructive Testing

dryrot1Tim Hutton of H+R, discusses the problems of dry rot in today’s difficult market conditions in the UK.

In these days of financial stringency and a sluggish property market, there are many buildings awaiting renovation or development. In this building equivalent of the ‘poverty trap’, maintenance programmes are often curtailed at the very time reduced occupancy puts the building at a higher risk of problems such as, water penetration and poor ventilation. These conditions often result in chronic problems of timber decay and especially dry rot, Serpula lacrymans. It can be difficult to fund works in these circumstances, as the managers will wish to minimise expenditure on remedial work which might be made irrelevant by further developments. At the same time, it is important to prevent rampant timber decay developing, as this devalues the property and increases the cost of eventual renovation. Examples of this conundrum can be found in every sort of property portfolio from Grade I listed historic building to office and domestic accommodation.

Hard to detect and eradicate, dry rot is generally perceived to be a special problem in buildings because it can be hard to detect and hard to eradicate. Its preference for growing behind surfaces, or in poorly ventilated cavities means that it is usually not detected until decay is advanced. Similarly dry rot’s ability to spread while hidden in cavities, behind surfaces and through masonry make it difficult and expensive to define the extent of an outbreak by traditional means.

Harefield House in Middlesex suffered such a fate and developed some dramatic growths of dry rot. The situation was not helped by repeated outbreaks of that common pest of unoccupied buildings, the greater spotted lead nicker, plumbus larcinus.

As the building was Grade II listed, the Property Services Agency, PSA, Conservation Unit was consulted for their advice. The problem described had been occupying the minds of the PSA and ourselves as their consultants for some time. For fifteen years we have been advocating a policy of controlling dry rot and other timber decay by manipulation of the timber moisture content, ventilation and temperature in the building. These techniques had proved highly effective and could be carried out at very low cost. The use of these techniques requires minimal work and loss of materials and reduces the final costs of renovation between 60%-90%.

The problem with this approach was that it was necessary to survey the building for all the active dry rot outbreaks, which could be time consuming. If precautionary works were to be minimised it was also desirable to repeat the survey at intervals of three to six months to check for any new problems and to monitor the regression or development of any dry rot infestations. The practice were commissioned to carry out a site visit with preliminary recommendations for the control of the dry rot problem in November 1989 at which time the outbreak was reaching epic proportions. We recommended a full survey but in the meantime were able to give instructions for a number of holding measures. However, because of the ‘building poverty trap’ it was not possible to fund a full survey and remedial works.

At this time we were in the middle of our ‘Rothounds’ project to train search dogs to find active dry rot in buildings. We had found that Rothounds could detect small samples of dry rot hidden under floors, behind plaster, in ceiling spaces, and when hidden by furnishings and finishes of all sorts. They also worked very quickly covering standard 4-bedroomed houses in five to ten minutes. We were therefore always on the lookout for larger properties to train in, so as to extend the search times. We also needed to train in Harefield House, a Grade II listed building awaiting renovation.