Timber
What is the difference between dry rot and wet rot?
Dry rot is Serpula lacrymans. Property Care Association guidance of August 2025 calls it the most serious form because it can spread through timber and into adjacent masonry. Wet rot is more common and is typically confined to timber that stays wet. Treatment differs. A dry-rot treatment on wet rot can be unnecessary.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless a source says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
How do dry rot and wet rot differ?
The Property Care Association’s fungal decay guidance, dated August 2025, separates the two. Dry rot is the fungus Serpula lacrymans. The guidance calls it the most serious form of fungal decay of timber because it can spread through timber and into adjacent masonry. Wet rot occurs more often and is less serious in that document’s terms. Decay is typically confined to timber that has become wet and stays wet. Wet rot does not, in the ordinary case, run through a dry building in the way dry rot can. Neither label is a price.
| Dry rot | Wet rot | |
|---|---|---|
| Organism named | Serpula lacrymans | Several fungi, not one species |
| How serious | The most serious form of timber decay in that guidance | More common, and typically less far-reaching |
| Where it stays | Can spread through timber and into adjacent masonry | Typically confined to timber that stays wet |
| Treatment | A dry-rot specification | A wet-rot specification, which is not the same job |
Why does the wrong rot treatment matter?
The August 2025 guidance says the two types have to be distinguished because they need different treatment. A dry-rot treatment carried out on wet rot can be unnecessary. The reverse mistake, treating dry rot as if it were only a patch of wet timber, is less certain of success because dry rot can already be in timber and masonry beyond the wet patch. This is a reason to identify the fungus, not a reason to buy the larger specification just in case.
Both still depend on water. Stop the leak, the bridging or the condensation that is wetting the timber, or the decay continues whatever is sprayed on it. The Property Care Association also describes wet rot as localised softening, cracking and discoloration, often with a damp smell. Those signs justify opening up where the surveyor could not see. They do not justify a dry-rot treatment across the house if the organism is wet rot.
What can a home survey see, and what can it not?
A RICS home survey looks at timber that is accessible. Skirtings, the edge of a floor, a cellar and a roof space may show decay. Fitted coverings, insulation and stored goods hide the rest. The Level 3 description is a thorough visual inspection, not an opening-up contract. The surveyor should say if they suspect dry rot or wet rot, and they should say if they could not see the timbers that would prove it.
Do not read a damp meter, or a musty smell, as a named fungus. Smell and staining are reasons to investigate. The name of the rot, and how far it has gone into masonry, comes from someone who can expose the timber and who is using the distinction in the fungal guidance. In England and Wales that investigation belongs before exchange if the survey has said the structure may be affected. A price cut with no opening-up leaves you holding both the uncertainty and the repair.
What should you ask if the report mentions rot?
Use the surveyor’s words. If they said wet rot, do not let a quote silently upgrade it to dry rot. If they said they could not tell, the next instruction is identification, not a combined treatment for every fungus they can name.
- Did you see dry rot, wet rot, or only conditions that might allow either?
- Which timbers were visible, and which were covered?
- Where is the moisture coming from, and is it still arriving?
- Would a dry-rot specification be unnecessary if this is wet rot?
- What opening-up do you want before exchange?
Common questions
What fungus is dry rot?
Dry rot is Serpula lacrymans. Property Care Association guidance of August 2025 calls it the most serious form of fungal decay in buildings because it can spread through timber and into adjacent masonry. Wet rot is a different group of fungi.
Is dry rot always worse than wet rot?
The August 2025 guidance calls dry rot the most serious form because of the way it can spread. Wet rot is more common and is typically confined to timber that stays wet. Serious still depends on where the timber is and whether the water is still arriving.
Can one treatment cover both dry rot and wet rot?
No. The two need different treatment. A dry-rot treatment used where the problem is wet rot can be unnecessary. Identify which fungus is present before you accept a specification.
Can the surveyor say how far dry rot has spread?
Only as far as they could see. Dry rot can extend into adjacent masonry, but a visual survey does not open floors or chase walls as standard. Any distance beyond the visible timber is an investigation, not a sentence in the report.
Does a damp smell mean dry rot?
A damp, musty smell can come with either dry rot or wet rot, and with damp that has not yet decayed the timber. The Property Care Association treats the smell as a reason to investigate, not as the name of the fungus. Ask for the timber to be seen.
What does wet rot look like?
The Property Care Association describes soft, weakened timber, often cracked, discoloured and losing strength, sometimes with fungal growth and a damp smell. It is typically localised to the wet area. Those signs still need someone competent to confirm the type.
If you dry the timber, does the rot stop?
Wet rot is typically confined to timber that stays wet, so stopping the water is essential. Dry rot can spread beyond the wet patch, which is why the type has to be identified. Drying the building is part of either repair, not a substitute for knowing which fungus you have.
Should you investigate rot before exchange?
Yes, if the survey says structural timber may be decayed and the extent was not visible. You would be buying an unknown repair. A specialist who can see the timber, and who will say whether a dry-rot treatment is unnecessary, is the useful next step.
Sources
- Guidance document: fungal decay in buildings (August 2025) — Property Care Association
- What does wet rot look like? — Property Care Association
- Structural problems, including damp, dry rot, wet rot and woodworm (homeowner advice) — Property Care Association
- Description of the RICS Home Survey Level 3 (condition rating definitions) — RICS
Key facts
- Dry rot
- Dry rot is Serpula lacrymans. PCA guidance of August 2025 calls it the most serious form because it can spread through timber and into adjacent masonry.
- Wet rot
- Wet rot is more common. It is typically confined to timber that stays wet, rather than spreading through the building in the way dry rot can.
- Different treatment
- The two need different treatment. A dry-rot treatment carried out on wet rot can be unnecessary.
- What wet rot looks like
- PCA describes wet rot as timber that is soft, cracked, discoloured and weakened, sometimes with fungal growth and a damp smell. It is typically localised.
- Survey limit
- A home survey does not open floors as standard. Hidden joists and wall plates may not have been seen, so the extent can remain unknown.