In general studies, roof construction including, pitch, thatch thickness and packing density as well as the skill of the thatcher and climatic conditions have all been cited as contributors to the longevity of a thatched roof. However, when assessing the causes for premature degradation it is important to recognise and identify these other conditions and to separate them from any alleged material failure associated with decay associated with contamination at the reed bed.
Premature degradation can be detected at a relatively early phase in the life of a roof, usually within 5 â€“ 10 years after thatching. Decay areas can be random and patchy with not all aspects of the thatch surface being involved. Early signs are light coloured patches and physical cracking on the surface often associated with surface clumping of the thatch, the problem is exacerbated by physical erosion from wind and weathering and is more obvious after periods of dry weather.
Thatchers across Europe, not just in the UK, have identified this type of decay, specifically in water reed harvested from some European reed beds. Reed from well managed reed beds in the UK is of high quality; harvest timing, cutting, cleaning, dry storage and reed conditioning do contribute to water reed quality for thatching, good reed bed management and post harvest storage conditions do contribute to water reed thatch longevity. Part of the problem is that demand exceeds supply for thatching reed and reed from marginal areas and over harvested sites is being sold to satisfy this demand. In wet reedbeds the butt may turn dark or black, this is a sign of good water management in young reed beds but in old reed it indicates a rapidly decaying biotype with advanced fungal attack. The butt ends of reed will be wetter and more subject to infection than the rest and living reed is more liable to decay. In providing remedial action for a thatch showing signs of this type of decay, the fact that attack takes place at the thatch surface makes recognition of the condition easier and for remedial action to be taken early. Early detection allows a thatcher to clean down the surface and to remove and replace any damaged patches, and to re-dress the thatch. It is seldom necessary for the whole roof to be re-thatched.
The National Society of Master Thatchers is currently engaged in a collaborative research programme to address the issues and is working with thatching organisations in Denmark, Holland and German and the Broads Authority and the British Reed and Sedge Cutters Association to find solutions.
New advances in the technology have led to solvent based borates for timber treatment that may be appropriate for treatment of small patches of decay in thatch. These require further investigation with the manufacturers and in the future may provide a solution to treating decay patches, but chemical treatment is some time away as any new application for new uses of chemicals requires certification before it can be adopted.