Both are fungal decay of timber caused by moisture. Wet rot stays where the timber is wet and stops when it dries, while dry rot (Serpula lacrymans) can spread through masonry from a damp source to reach other timber, so it needs prompt, thorough treatment. In both cases, the source of moisture must be fixed.
The names are confusing. Both need moisture, and so-called dry rot only gets its name from the dry, crumbly state it leaves timber in. What really separates them is how they behave.
Wet rot
Wet rot is a general term for several fungi that attack timber that’s wet. It tends to stay put, confined to the area that’s being kept wet. Typical places are window frames and sills, door frames, skirtings and joist ends against damp walls, and timber under leaking baths and showers.
Signs include timber that’s soft and spongy, darkened, cracking along the grain, or crumbling when you push a screwdriver into it. Paint may look fine on top while the wood underneath has gone.
Fix the moisture, and wet rot stops. Badly decayed timber needs cutting out and replacing, and the remaining timber can be treated where appropriate.
Dry rot
Dry rot is caused by one particular fungus, Serpula lacrymans, and it’s the one that worries people for good reason. Given damp timber to start on, it can produce strands that travel across and through masonry, plaster and behind skirtings to find more timber. It typically likes damp, still, unventilated areas: subfloors, behind panelling, in cellars, under stairs.
Signs include:
- White, cotton wool-like growth in humid conditions, or a grey, silky skin.
- Strands, sometimes as thick as a pencil, running over masonry.
- Timber with deep cracks across and along the grain, breaking into cube-like pieces.
- Fruiting bodies, which look like a pancake with a rusty-orange centre, and rust-coloured spore dust.
- A strong mushroom smell.
Treating it
With dry rot, the key steps are finding and stopping the moisture source, opening up to find the full extent of the outbreak, removing affected timber beyond the visible damage, treating surrounding masonry and timber where needed, and getting the area drying and ventilated. Without moisture it can’t keep growing, so drying the building matters most.
Be wary of being told your whole house needs gutting. Equally, don’t ignore it. Get a proper inspection.
When to call a specialist
If you suspect any kind of rot, especially dry rot, get a damp and timber survey promptly so the extent and cause can be found. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Frequently asked questions
Can dry rot spread through walls?
Yes, dry rot strands can travel across and through masonry to reach other timber.
Will wet rot spread?
It generally stays where the timber is wet and stops once the timber dries out.
What's the first step in treating rot?
Find and fix the source of moisture.