Part of Ward Property Services UK LtdGuides
Dry Rot vs Wet Rot: How To Tell The Difference
Identifying dry rot
Dry rot, Serpula lacrymans, produces deep cuboidal cracking across the grain, white cotton-wool mycelium, grey-white strands capable of crossing masonry, and rust-red spore dust from a fleshy fruiting body. There is usually a strong mushroom-like smell.
Its defining ability is transporting moisture through its own strands, which lets it spread from a wet area into timber that is otherwise dry — behind plaster, under floors and through walls. This is why treatment must chase the full extent of the growth, not just the visibly decayed wood.
Identifying wet rot
Wet rot fungi decay only persistently wet timber and do not spread into dry material. The wood feels soft and spongy, darkens, and cracks along the grain rather than across it. There are no travelling strands and no large fruiting bodies.
Typical locations are window sill bottoms, door thresholds, joist ends built into damp external walls and timber in unventilated sub-floor voids. Because damage stays local, repairs are usually far more contained.
Treatment and cost implications
Both start the same way: find and stop the water. From there, wet rot often needs only the decayed section spliced or replaced and adjacent timber treated. Dry rot requires exposure of the full extent, removal of timber beyond the last visible growth, masonry treatment and replacement in pre-treated timber.
Because of that difference, an incorrect diagnosis is expensive in either direction — unnecessary opening-up if wet rot is called dry rot, or a recurring outbreak if dry rot is treated as wet rot. Identification on site by someone who deals with both is worth the survey fee.
Common questions about this topic
Does dry rot mean major structural work?
Not always. Outbreaks caught early can be contained to a small area; the extent depends on how long the moisture source has been active.
Can I treat rot myself?
Surface preservative on minor wet rot is feasible, but any structural timber or suspected dry rot needs professional assessment.
Need professional advice?
Book an independent damp survey and get a written diagnosis for your property.