ecay in buildings due to attack from the dry rot fungus, serpula lacrymans, is common in Europe. It causes breakdown of timber and even spreads through brickwork and masonry behind plaster. The result is a serious loss of structural strength.
The rot sets in. Dry rot invades structural timber.
Traditionally, control has been by removal and replacement of the infested timber and brickwork, followed by chemical treatment of the remaining materials. Workers at the Danish Technological Institute, Taastrup have developed a much less invasive method of treatment, using heat to kill the fungal mycelium within the structures and leaving it in place. There is no need to replace wood and brickwork attacked by the fungus, unless it has become structurally unsafe. The heat treatment method is much quicker and cheaper, and avoids the destruction of often culturally important buildings.
The only problem with the heat treatment method is that it has to be totally effective, or it fails. If any of the fungal mycelium remains viable, it quickly spreads again and the infestation is soon as bad as before. Therefore a quality control system for the method was developed in Denmark, to ensure complete and effective eradication.
The primary aim of the Innovation project, Heatcon(1), was to establish a model for the transfer of the Danish heat treatment method to Norway. Project co-ordinator Anne Pia Koch of the Danish Technological Institute says that one of the main reasons the Norwegians were so interested in the technology is that the Municipality of Oslo had a lot of important historic buildings in need of treatment. The Municipality had already adopted general policies for building renovation, which required that the methods and materials used should have minimal effect on the environment, so the heat treatment was ideal. "The Institute trained five Norwegian contractors to do the heat treatment and a building surveying company to do the project planning," says Koch.
However, working on the transfer of the heat treatment process to Norway revealed the absence of any form of quality control, so essential for this system. "We discussed this with the Norwegian partners and explained how important it was for them to back the technology with an effective quality control system," Koch recalls. "This would also help to raise awareness and improve the quality of work in treating decay in general."
A building clad and ready for heat treatment - no need to tear out the decayed timber.
Quality control body
With the advice of the Danish Technological Institute, a group of independent Norwegian heat contractors (KVH) has been set up to oversee the quality of heat treatment for dry rot control. They have established a quality control manual and ensured its compatibility with other regulations in Norway. They are in touch with the Danish quality control body to exchange information and experience. "However, we did not try to impose the Danish system, but to make them think about what they wanted in Norway," says Koch.
The KVH will also have the power to carry out inspections. If a heat treatment is found not to be of the required standard, it has to be done again at the contractor's expense. The next time such a contractor uses the method he might be subject to an independent check on his work. The ultimate sanction is to remove him from the group. This would not stop him using the heat treatment method, as the control is voluntary, but he could no longer claim compliance with the quality standard. Koch stresses the importance of proper marketing, so that when the owners of buildings choose the heat treatment from a contractor recognised by the quality control group, they know that they will benefit from the standard.
Extending still further
One of the factors which helped in the uptake of the heat treatment method in Norway was the presence of a major customer in the negotiations. The Municipality of Oslo had already experienced the technique - brought in specifically to rescue a major renovation project which was almost finished when serious dry rot was discovered in the roof. Using heat treatment made it possible to complete the project without having to redo the work at massive cost. Introduction of the method was also supported by architects in control of the maintenance of major state and royal buildings.
The Danish Technological Institute believes that the heat treatment process has a strong future. Given its initial success in Norway, approaches have been made to some other countries including Germany. The main obstacles seem to be conservatism, and the need to demonstrate real benefits over the traditional chemical method of treatment. However, the environmental and cost benefits of heat treatment should make it a popular alternative if its effectiveness can be guaranteed - which it can, now that quality controls are in place.
(1) Project IN1049 - Transfer of heat treatment technology as a means of controlling the dry rot fungus, serpula lacrymans, in buildings.