Dry Rot

Dry rot is a misleading name as the timber has to be damp for it to occur >28% moisture content, but after germination, the fungus can survive in 20-22%, which are lower than the other major wood-rotting fungi.  There is nothing dry about dry rot except, the visual damage to the timber after it has been consumed by the fungus.

The S. Lacrymans 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 water.

 Therefore despite its destructive reputation, dry rot has a high degree of sensitivity to its environment.

At a late stage of the infection large brown cuboid damage with thick strands would normally be visible.

Dry rot affecting treated timber via a cut in the timber.
fresh fruiting bodie of Serpula Lacrymans

Its fruiting body often occurs when the outbreak is distressed due to lack of water or woodie mater (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. this is why it is found extensively in period properties.

Is there a cure

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 wood rot.

Rapidly remove the water 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 try to engineer out chemical treatments at the specification stage and any treatment used should be targeted.

Nonchemical treatments

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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