Dry rot in the UK Serpula Lacrymans (previously known as Merulius Lacrymans)
Dry rot is misleading name as the timber has to be wet for it to occur >28%, but after germination, the fungus can survive in lower moisture contents (20-22%), which are lower than the other major wood rotting fungie. There is nothing dry about dry rot except, the visual damaged to the timber after it has been consumed by the fungus.
Large brown cuboid damage with thick strands would normally indicate that the decay has been going on for a long period of time. Its fruiting body often occurs when the outbreak is distressed (It is the flower of the fungus).
Dry rot will not live in masonry (without a wood source), the strands bringing nutrients back to the main body to help balance its digestive system and can pass through weak lime mortar or render, but not solid stone or brickwork.
The fungus requires an initial germination temperature of between 21 and 25°C preferred pH level in the acid to neutral range, limited air movement and a suitable water supply (28-30%). Therefore despite it destructive reputation, dry rot has a high degree of sensitivity to its environment.
Some Background info
An inspection must be carried out with special attention to the structural timber sections, which should be drill tested, where possible to find the extent of any decay. A dry rot sensor can be helpful in mapping out the infestation or monitoring.
Rapidly remove the moisture responsible (in all cases). This is not as straightforward as it sounds as there can be numerous reasons for the delay. This is the main justification for chemical treatments.
In all cases we try to engineer out chemical treatments at the specification stage and any treatment used should be targeted.
A non-chemical treatment option briefly involves building envelope repairs, structural repairs with steel or slow grown durable timber (i.e. West Coast Douglas fir) and membranes, combined with the installation of ventilation or a moisture sink of some kind. These works are monitored with moisture sensors combined with a building maintenance schedule.
Heat treatment has been used in Denmark by heating the building to 50°C over a 16 hour period.
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