Dry rot, wet rot and other forms of fungal decay

Fungal decay is the term given to all wood rotting fungi, of which there are a number of commonly occurring species, spread by microscopic airborne spores 

dry rot on the underside of a basement floor

dry rot on the underside of a basement floor

Timber is one of the most versatile building materials that we have available to us, the reason for this is that it can be replaced, i.e. it can be re-grown. However, because it is an organic material in origin it can therefore be degraded and whilst it is a replaceable commodity, replacement can be very expensive. There are basically two sources of degrading, that is ‘chemical degrading’ the other being ‘biological degrading’, this being either by fungal decay of by insect attack.

Dry and wet rot decay is responsible for thousands of pounds worth of damage to buildings every year, due to poor maintenance and repair, resulting in the degeneration of roof, floor and joinery timbers which can eventually result in structural collapse and weakening of a building’s fabric. Wood boring beetles can also if left to their own devices cause serious damage to timber again resulting in structural weakening of a roof and floor timbers.

Fungal decay is the term given to all wood rotting fungi, of which there are a number of commonly occurring species, spread by microscopic

Dry rot in panelling

Dry rot in panelling

 airborne spores. When these fungal spores settle on the surfaces of damp timber, they germinate and develop fine thread-like filaments called hyphae which penetrate the timber. The hyphae then release chemicals called enzymes into the surrounding timber.

The decay of the timber is caused by the process of these chemicals dissolving nutrients in the timber, the nutrients are then absorbed by the fungal hyphae, enabling the growth to take place. If the moisture content should fall below about 22% then this mechanism can no longer operate and the decay process stops, above 22% the growth extends through the timber through a fine network of threads called mycelium.

The mycelium of different fungi varies in colour and appearance and this aids in the identification of the growth. From time to time the fungal cycle is completed by the production of a spore bearing fruiting-body on the surface of the decaying timber. As with the mycelium growth, the shape colour and appearance of the fruiting body will vary, which can also aid identification of the decay.

Non wood rotting fungi

Non wood rotting fungi

However, not all fungi found in buildings will cause wood to decay, although others can cause catastrophic damage resulting in considerable expenditure and repair work. It is therefore that the correct identification of fungal decay is made during a survey so as to ensure that the correct repairs are specified, as the incorrect identification can result in unnecessary expenditure, treatment and repairs but more importantly the loss of the buildings fabric.

There are basically two main types of wood-rotting fungi found in buildings; wet rots and dry rot and it is not always necessary to distinguish between the many species of wet rot, as the remedial measures are generally the same for most of them. However, the successful treatment and eradication of dry rot can be more elaborate and generally more destructive and it is therefore essential that the diagnosis is correct so as to avoid unnecessary expense, inconvenience and more importantly irreversible loss and damage to the fabric of the building, particularly when dealing with period and buildings of historic interest.

Common Wood Rotting Fungi;

Dry Rot- (Serpula lacrymans)
Considered to be the most destructive of all wood rotting fungi causing extensive damage to timber embedded or in contact with wet masonry. Attacks both soft and hardwoods and is able to grow through and over masonry and mortar allowing the fungus to spread to dry wood if in un-ventilated conditions. Cuboidal cracking of timber or the appearance of fruiting body / spores is normally the first indication of a dry rot outbreak. Statistics indicate that moisture sources responsible for most of the recorded Dry rot attacks result from defects in down pipes and guttering systems.

Wet Rots – (Coniophora puteana)
Commonly know as cellar fungus and is the most common cause of decay in woodwork affected by water ingress. Attacks most types of soft and hardwood timber.

(Fibroporia vaillantii)
Commonly referred to as white pore or mine fungus. The poria species of fungi are a common cause of timber rot in domestic buildings, particularly in areas where high temperatures and poor ventilation exist. Attacks most soft and some hardwoods.

(Phellinus contiguus)
Common decay affecting external joinery timbers. Attacks soft and hardwoods. Timber bleaches and will eventually develop a stringy fibrous appearance, but unlike other wet rots there is no cuboidal cracking.

(Asterostroma spp)
Common cause of fungal decay to softwood skirting board joinery. Timber bleaches and will eventually develop a stringy fibrous appearance, but unlike other wet rots there is no cuboidal cracking and timber does not crumble.

(Donkioporia expansa)
Common decay affecting timbers where there has been persistent water leakage. Attacks mainly hardwoods (oak) but can spread to adjacent softwood timbers. Decay is often associated with infestation by Death Watch Beetle.