Damp, mould and structural
Dry rot: how to identify and treat the most serious timber decay
Dry rot is a fungus (Serpula lacrymans) that decays damp timber and, unusually, can spread across dry masonry to reach new wood. It leaves timber cracked into cubes with a musty smell and rusty-red spore dust. It is the most serious timber decay in UK homes and needs a specialist to treat the rot and the moisture source.
- Also known as
- Serpula lacrymans, true dry rot
- Easily confused with
- wet rot, woodworm damage, general damp staining
- How serious
- High: spreads through masonry and weakens structural timber
- Typical cost
- Usually no cost for DIY control
How to identify dry rot
Affected timber becomes dry, brittle and cracks into distinctive cube-shaped pieces (cuboidal cracking) that crumble easily, with a strong musty, mushroom-like smell.
Dry rot produces fine grey or white sheets of mycelium, sometimes with lilac or yellow tinges, and grey strands that can spread across brick and plaster. A fruiting body looks like a soft pancake with a rusty-red centre, and rusty-red spore dust may settle on nearby surfaces.
It starts in damp timber but, unlike wet rot, can travel through and over dry masonry to attack sound wood elsewhere, which is what makes it spread.
How serious is it?
High: spreads through masonry and weakens structural timber
Dry rot is the most serious of the common timber decays because it can spread beyond the original wet area and weaken structural timber such as joists and roof timbers.
The Property Care Association treats dry rot as a job for a competent timber specialist: the decayed wood is removed, the moisture source is cut off, and remaining timber is treated. Cosmetic patching without addressing the moisture allows it to return and spread.
How to fix it yourself
- Find and fix the moisture source, because dry rot cannot survive without dampness: trace leaks, blocked gutters, penetrating damp or poor ventilation feeding the timber.
- Improve ventilation to under-floor and roof voids to help timber dry, which removes the conditions the fungus needs.
- Remove and safely dispose of obviously crumbling, infected timber only where it is safe to do so and not structural.
- Do not assume a spray alone will solve it: dry rot in structural timber is a specialist repair, not a DIY treatment.
When to call a professional
- You find cuboidal cracking, grey or white mycelium sheets, red spore dust, or a pancake-like fruiting body, especially on structural timber.
- The affected wood supports floors or the roof, or the rot may have spread through masonry to other timber.
Who to call
- A timber decay specialist, ideally a Property Care Association member, to identify and treat dry rot and specify repairs.
- A structural engineer if load-bearing timber such as joists or roof members is affected.
Frequently asked questions
How do I tell dry rot from wet rot?
Dry rot cracks timber into cubes, produces grey or white mycelium and rusty-red spore dust, and can spread across dry masonry to fresh wood. Wet rot stays in the wet timber, often looking darker, softer and stringy or spongy. Dry rot is the more serious and more invasive of the two.
Is dry rot dangerous to a house?
It can be, because it weakens structural timber such as floor joists and roof members and can spread beyond the original damp area. It is the most serious common timber decay and the Property Care Association recommends a specialist assessment rather than DIY treatment for anything structural.
Can dry rot be treated?
Yes. Treatment means cutting off the moisture source, removing decayed timber, and treating the remaining wood, usually carried out by a timber specialist. Treating the rot without fixing the dampness fails, because the fungus needs moisture to live, so the moisture fix is the essential part.
Sources
Editor, HomesAndHedge
Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.
Last reviewed: 8 June 2026