True Dry Rot

Dry rot is the common name given to the wood rotting fungus, Serpula Lacrymans. Despite its common name, it generally attacks timber which has been subject moisture ingress.

The dry rot fungus is significant for its ability to spread extensively behind plaster and through wall materials.

Fungal decay in timber is caused by high moisture content. Providing timber is kept dry, it should not decay. Untreated damp timber is at risk of decay by one or more of the many wood rotting fungi.

Spores are present in the environment and potentially present in all properties. However, a spore will only germinate where both food and water, i.e., dampness and a food source, wood and some other cellulose based materials. Moisture must be present for spore germination.

Once initiated, hyphae and mycelium of the fungus can grow through and over damp masonry in search of further cellulosic based materials to attack. Unprotected timber in contact with damp masonry are at risk of attack, e.g., joists, lintels, panelling, fixing grounds, skirting and any other timber which becomes damp or wet.

Dry Rot

Dry rot, Serpula Lacrymans, is a destructive fungus, which attacks timber in moist conditions (20–30% moisture content). It causes wood to shrink, crack in a cuboidal pattern, and become brittle, often appearing with white, cotton-wool-like mycelium or orange, rusty spores. It requires fixing the moisture source, increasing ventilation, and replacing damaged timber.

Dry Rot, Serpula Lacrymans causes structural defects in buildings. It is unsightly and unhealthy and can grow at a rapid rate. Defects are caused by damp ingress, leaks, poor ventilation and poor maintenance.

Dry Rot is the most serious of wood rotting fungi. For fungal decay to begin it requires water to penetrate wood which then allows bacteria and micro fungi to colonise resulting in the partial breakdown of the cell structure. The timber becomes more porous and potentially wetter. If the moisture content is sustained above 30% then Dry Rot can colonize and germinate leading to decay.

As Dry Rot spores are airborne this means that all buildings are susceptible to attack given the right conditions. Once germination is established the fungus can spread rapidly, though thick masonry walls, in search of timber causing potentially extensive damage if not treated at the earliest instant.

The History of Dry Rot

Originally known as Merulius Lacrymans (meaning Tears of the Blackbird as it was thought originally that the fungus was spread by blackbirds) the fungi now known as Dry Rot can be traced back to 1720. By 1827 the name had changed to Serpula Lacrymans because of the snake like growth of the hyphae which eventually come together to form mycelium growth. At the ends of the hyphae, tear like droplets of water appear (this is the Dry Rot’s way of controlling moisture) hence the term Lacrymans meaning tears.

The Lifecycle

Like woodworm, fungi have life cycles and probably the most economically important species of fungal decay in buildings is True Dry Rot, serpula lacrymans.

Dry Rot requires three elements to grow in timber, water, air and a food source. The fungus obtains its food from the timber by breaking down the cell walls resulting in a loss of strength and collapse.

When the timber has an optimal moisture content of between 25% and 30% for germination and the correct environment, the lifecycle starts with a spore landing on the timber. The spores are omnipresent and in the atmosphere all the time. If a sample of air was taken in a room and micro filtered, it would be likely to contain fungal and mould spores, including dry rot.

As the spores land on the damp timber, they germinate to produce hyphae growth. This is similar to seeds in damp compost. The hyphae growth is the root of the spores. The hyphae growth then mass and colonise together to produce mycelium, white and “fluffy” in appearance. After a period, the Dry Rot becomes stressed, which occurs when one of the three necessary elements for growth (water, air or food) is removed or if the dry rot is subject to light.

When stressed it produces a sporophore or fruiting body which is a self-reproduction organ. This allows the spores to shed into the atmosphere allowing new spores to land again with the aim of finding suitable conditions to continue germination and extending the Dry Rot growth.

Wet Rot fungi, whilst generally not as destructive as dry rot can also cause severe damage if allowed to go unchecked and is a common cause of structural defects. Wet rot is commonly found in timbers in contact with damp masonry. Typical signs include localised fungus which is mainly black in colour. Another key identifying factor of Wet Rot is the colour of the decayed and rotten timber as well as the size and type of cracking of the timber.

Areas We Cover

We build house extensions and loft conversions across Barnstaple and North Devon, including:

Barnstaple, Bideford, Ilfracombe, Braunton, Northam, Appledore, Instow, South Molton, Torrington, Woolacombe, Combe Martin, Lynton & Lynmouth, Umberleigh — and surrounding areas — plus wider Devon by request.