Dry rot in the UK Serpula Lacrymans

(previously known as Merulius Lacrymans)

Dry rot fungus is the most important timber decay fungus in buildings in Europe. The Himalayas is the only area where it is found in the wild (to date).

The name dry rot can be confusing as the timber has to be wet for it to occur (20% to 28%).  The name has been around for at least 200 years and mostly describes the effect of the brown rots.  In the early 1960’s the brown rots were re-assessed and Serpula Lacrymans was allocated the sole name dry rot to separate it from the other brown rots.

Despite a justified destructive reputation, Serpula Lacrymans has a high degree of sensitivity to its environment. The fungus requires an initial growth temperature of between 21 and 25°C preferred pH level in the acid  to neutral range and  limited air movement with a wood moisture content of above 20%.
Extensive brown cuboid damage with thick strands would normally

indicate that the decay has been going on for a long time.  
A dry rot fruiting body normally 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.   The fungus also has the ability to use rock wool as a mineral source.

Control

An inspection must be carried out with special attention to the structural 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 have a duty to try and engineer out chemical treatments at the specification stage and any treatment (I.e. Boron) used should be targeted.
• The non chemical treatment option briefly involves the normal 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 then monitored with moisture sensors combined with a building maintenance schedule.
• Heat treatment of the building has been used in Denmark successfully since 1989.  The dry rot is killed by heating the building to 50°C over a 16 hour period.