What is Dry Rot (Merulius Serpula Lacrymans) in a nutshell?

The mention of Dry Rot usually puts people on their guard and to reach for their bank statement to check ones funds.

It has to be said that having Dry Rot in a property can be costly to eradicate, this is mainly due to this type of fungus being capable of spreading over quite an area and causing damage to structural timbers as well as door frames and window frames and other joinery timbers.

Dry Rot is probably the best known of all wood destroying fungus.

It tends to develop in concealed areas with poor ventilation. There has to be the right conditions for germination, requiring a narrow range of atmospheric relative humidity and wood moisture content. Germination would occur easily in acid conditions thus timbers having already been affected by wet rot decay can prove ideal.

Dry Rot produces hyphae which are white in colour. They are very fine tubes which branch and increase in length and spread in all directions from the original germination point, providing there is a sufficient food source.

Growth is inhibated at times through seasonal changes and resumes again when more suitable conditions return. Hyphae contract when drying out to form layers or mycelium, each layer denotes a season of growth.

In unventilated conditions active growth can give the appearance of cotton wool with perhaps droplets of water on it. This is the way the fungus regulates the humidity. The latin name ‘lacrymans’ means to weep/cry hence the tear like droplets.

The mycelium/Rhizomorpus are relatively brittle, unlike those of wet rots, and can travel/spread over large areas through, brickwork, masonry, behind wall plaster etc spreading through walls into adjacent properties ensuring a build up of infection even if all decayed timber is removed. Any treatment of sound wood and replacement timber with preserved wood should always be in conjunction with chemical sterilisation of mycelium infested brickwork.

When exposed to light, mycelium, which is usually grey, can become yellowish with lilac tinges and often subsequently green in colour through development of mould growth.

Sporophroes or fruiting bodies generally develop when the attack is understress perhaps through a temperature change, food supply ending or moisture source decreasing.

Sporophores are like flat plates or brackets and can be from an inch to three feet or more across. They are grey at first with the edges a margin of white. The surface then corrugates slightly in the centre and is soon covered in millions of rust – red spores which are eventually let loose into the air covering the surrounding area in red dust.

A company carrying out surveys in respect of dry rot would usually want to expose areas in order to ascertain extent of the attack and the damage caused, prior to being in a position to give an appropriate cost for remedial works/treatment.