Dry rot and wet rot are both wood-destroying fungi, and both start with timber that has stayed damp for too long. But they behave very differently, and treating one as the other can mean either unnecessary work or a problem that keeps spreading.
Wet rot: the more common of the two
Wet rot is a general term for several fungi that attack timber with a high moisture content. It usually stays close to the source of water, such as a leaking gutter, a failed window sill, a bathroom leak or a timber in contact with damp masonry.
- Timber feels soft and spongy, and may look darker than the surrounding wood
- The surface can crack along the grain, or break up into small pieces
- Paintwork on skirting boards and window frames may hide decay underneath
- The damage is usually confined to the wet area
Once the water source is fixed and the timber dries, wet rot stops. Affected timber is cut out and replaced or repaired, and nearby timber can be treated as a precaution.
Dry rot: less common, more serious
Dry rot (Serpula lacrymans) also needs damp timber to start, but once established it can spread through masonry and across dry areas in search of new timber. That is why it is treated with more caution.
- Timber shrinks and cracks into cube-shaped pieces
- White, cotton-wool-like growth in damp, still areas, sometimes with grey strands
- Flat, pancake-shaped fruiting bodies with a rusty-orange centre
- Fine red-brown spore dust on surfaces nearby
- A distinctive damp, mushroomy smell
Why the difference matters
Wet rot is mainly a moisture problem: fix the leak and repair the timber. Dry rot needs the moisture source fixed, the full extent of the outbreak traced, affected timber removed beyond the visible damage, and the surrounding masonry treated where appropriate. Getting the diagnosis wrong can mean far more opening up than necessary, or an outbreak that carries on spreading behind plaster and under floors.
What to do if you find rot
- Don’t strip out timber or plaster yourself before it has been inspected. It can make the diagnosis harder.
- Look for the water source: gutters, downpipes, plumbing, blocked air bricks and bridged damp proof courses are common culprits.
- Book a timber survey with a Property Care Association (PCA) qualified surveyor.
Our surveyors identify the type of decay, find the cause and recommend only the work your building needs. Find out more about our dry rot and timber treatment service, or request a survey.
