Dry Rot

Dry Rot (‘serpula lacrymans’) is a type of wood-decaying fungi that can cause severe structural damage to buildings by weakening and destroying the timber found in floorboards, skirting, joists and other wooden surfaces. It feeds by sucking moisture out of affected wood, leaving it relatively dry and shrivelled (hence the origin of the name).

Identifying Dry Rot
‍
Early identification of Dry Rot is not always easy because it can look very similar to less damaging Wet Rot. Because its appearance is constantly changing throughout the lifecycle it often gets misdiagnosed, leading to inappropriate treatments. 
Initial signs to the onset of rot include irregularities in the surface of joinery and hairline splitting along and across the grain of the wood that a knife blade can easily penetrate.
‍
Dry Rot may be detected by its distinctive mushroom-like smell. More commonly, identification becomes considerably easier once it develops distinctive cobweb like strands of white or grey hyphae that morph into mycelial growth (vegetative part of a fungus) - that look a bit like tufts of cotton wool with colourful patches. In its final stages the mycelium morphs into a pancake-like ‘fruiting body’ that emits millions of spores in the form of red dust, starting the cycle over again.
‍
Decayed wood takes on a darker brown, crumbly appearance with deep cuboidal cracking and, if handled, the affected wood will disintegrate into powder.
‍
Causes of Dry Rot
‍
The term ‘Dry Rot’ is in fact a bit misleading because all wood-destroying fungi need a certain amount of moisture for decay to take hold. And even though dry rot is not to be confused with wet rot, it is also a type of fungi that thrives in moist conditions attacking timber to extract nutrients. For timber to initially become vulnerable to attack it needs a persistently high moisture content. Once established however, the fungi can remain active in timber with a lower moisture content of only around 20%.
In suitable conditions spores can germinate within a couple of weeks. Left untreated, rampant fungal growth can eventually spread throughout a building, travelling 2-3m in a year.
‍
Where is Dry Rot Found?
‍
The most common place to find outbreaks of Dry Rot is in damp cellars and sub-floor voids particularly where ventilation has been blocked. Roof spaces also sometimes play host where water leaks from defective flashings etc have been allowed to persist resulting in high humidity, again compounded by poor ventilation. Hidden from plain sight, the fungus may be quietly spreading and eating away at structural timbers such as joists or rafters before homeowners notice any signs of infestation. 
Symptoms are more readily visible in skirting boards, wood panelling or timber studwork. Defects such as concealed plumbing leaks or poorly sealed baths and shower trays can promote ideal conditions for rot to develop in adjacent timbers. 
Although masonry contains no nutrients for the fungi to consume, once the mycelial growth becomes rampant, it can colonise porous brick or stone walls spreading through mortar joints in search of timber to attack, especially in older properties.

Dealing with Dry Rot

Remove the moisture source and promote rapid drying of timber with high moisture content. Application of fungicides and biocides repair damaged wood. Kill off the existing infestation. Replace any damaged timbers with pre-treated timber.

What are the Differences Between Dry Rot and Wet Rot?
‍
It can be difficult to differentiate between Dry Rot and Wet Rot due to the fact that both types of rot share a number of tell-tale signs.
Both cause timber to crack, leave affected areas soft and spongy and can lead to fungus-like growth on timber.
One of the main differences between Dry Rot and Wet Rot is that wet rot requires a higher moisture content of around 50% whilst dry rot will grow with a moisture content of around 20-30%. Because of this, Wet Rot will only be present near a prevalent moisture source and as such is often found in the vicinity leaking appliances, burst pipes or window sills. In contrast, dry rot can spread over relatively dry timber if the humidity is right.
Due to the difficulties in identifying the type of rot, we  recommend contacting a rot specialist who can examine any affected timber and establish if there is a rot outbreak!

‍