Timber decay and woodworm

Wet rot in one window sill is not an attack on the floors. Why should you not price a whole-house timber treatment from that sill?

Because wet rot stays with the timber that is wet. A soft sill is a window and weathering repair, not proof that the floor joists are decaying, and it does not justify spraying the house. The Property Care Association treats wet rot as a moisture problem first. The survey has not opened the floors because a sill was soft.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

Window sills get wet from rain, failed putty and blocked drips. The rot is local. A contractor who turns one sill into a chemical treatment of every floor is selling a different job from the one the survey described. The floors may be fine, or they may have their own defects the inspection could not see under coverings. Those are not proved by the sill. A standard home survey does not lift fitted carpets to chase a window defect into the joists.

Ask the surveyor which sills were soft and whether any floor timber was actually tested. If none was, keep the quote for the windows. Repair the joint that is wetting the sill, and replace the timber that has lost its strength. Do not accept a “whole house” figure that starts from one piece of joinery. If you later find a soft floor, that is a new investigation with its own moisture source. The sill quotation should not be allowed to stand in for it.

What should you ask your surveyor?

Which sills are affected, and did you see any floor timber at all?
What is wetting this sill: the joint, the glazing, or something else?
Are you recommending treatment beyond this window? If so, what did you see?

What are the typical next steps?

Get a joinery quote for the sill and the weathering, not a house-wide spray.
Do not lift floors solely because a sill is soft.
If a floor comment exists elsewhere in the report, deal with that comment on its own evidence.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Can wet rot in a sill spread across dry masonry into a joist?

Wet rot needs the timber to stay wet. A dry joist across the room is not that sill. The PCA’s point is moisture, not a cloud of treatment.

Does one soft sill mean the other windows will be rotten?

No. Each window is its own piece of timber. Ask which ones were probed.