Dry Rot

Dry rot’ Serpula lacrymans is a fungus that decays wood, The name derived from serpent like and the tear ducts which produce moisture. The discovery of dry rot in a property can be very worrying to a property owner. Dry Rot is a destructive fungus but with professional surveying and remedial works it is completely treatable.

All wood-rotting fungi require both food (wood or other cellulosic material) and water, and the dry rot fungus is no exception; deprived of either, it cannot survive.

There is a lot of  mythology surrounding dry rot fungus which is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry area. The strands do transport water but they have to be in a humid unventilated situation otherwise water will evaporate very quickly. Dry rot will only grow in ideal conditions and once discovered and exposed / ventilated will form sporophores to try and propagate in other ideal situations by throwing spores into the air.

The worst outbreaks are normally found in buildings under or behind unventilated floors and timber walls with a source of moisture and a high humidity. Another common cause is timber building elements built directly into damp masonry.

CONTROL MEASURES

Diagnosis of any sources of moisture by a qualified timber surveyor is critical to curing Dry Rot.

Because of the nature of dry rot it is important that the opening up (removal of floors and plaster) to investigate the extent of the outbreak is carried out under the supervision of the qualified LSE remedial surveyor so as the full extent of the Dry Rot can be ascertained and drawn and mapped out but without causing unnecessary destruction to unaffected areas and finishes which may be unnecessary or of historical importance.

If an area of timber or plaster affected by Dry Rot is of historical importance then every effort should be made to conserve it by drying , isolating and if necessary treating with Boron. The area or building element should then be monitored either visually or with Dry Rot sensors and damp sensors which are now available through LSE.

Isolation of all timbers from damp masonry is essential as a long term cure for the Dry Rot.

Treatment with Boron can be carried out to help prevent further outbreaks. As a masonry biocide B10 will effectively eradicate spores and Fungal Growth in the wall. B20 will work very effectively on damp masonry and will remain in dry wood as a defense should it become damp at which point the B20 would move into the wood to give further protection.

All new timber used in repairs should be pre-treated with a wood preservative. Detailed guidance on the treatment required for various timber components is given in the British Standard BS 5268: Part 5, which deals specifically with structural timber, and BS 5589 which covers a wider range of uses.

Guidance is also given on the use of naturally durable timbers (see also Digest 429 published by the Building Research Establishment Ltd).