Timber decay and woodworm
The timber sill of one window is wet-rot soft and the frame above it is firm. Why is that sill not a diagnosis of dry rot in the floor?
That sill is not a diagnosis of dry rot in the floor because the decay found is local wet rot in one window sill. Wet rot stays where timber has remained wet. The frame above the sill was firm, which keeps the finding on the sill rather than on a fungus travelling through the joinery. The floor was not the subject of the note and was not opened. The survey has identified a soft sill. It has not diagnosed dry rot, has not said the floor is affected, and has not specified that floor timbers be replaced.
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?
Wet rot and dry rot are different. Wet rot needs the wood to stay damp, and it is common in sills that catch rain. Dry rot is a different organism that can put strands through drier timber and travel beyond the wet spot. A soft sill with a firm frame does not show those strands and does not show a floor. Using the sill to condemn the floor skips the evidence and names the wrong fungus. The inspection recorded what was soft and what was firm at that window.
A joiner can splice or renew the sill and sort the wetting that softened it, which is often the paint, the drip or the masonry joint rather than a floor fungus. Tell the solicitor the report is a window sill, not dry rot in the floor. The survey has not opened the floor and has not instructed a dry-rot contractor. If you later see strands, a mushroom smell or cracking in skirtings, that is a new note. It is not what this sill has already proved.
What should you ask your surveyor?
- Was the softness limited to the one sill, with the frame above still firm?
- Did you see any dry-rot strands, or only wet rot in the sill?
- Was the floor opened, or left out of this note?
What are the typical next steps?
- Treat the soft sill as local wet rot, not as dry rot in the floor.
- Have a joiner repair the sill and the detail that keeps it wet.
- Do not open or replace the floor on the strength of this window.
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
If the wall under the sill is damp, has dry rot started in the floor?
A damp wall under a sill explains how the sill got wet. It is not a diagnosis of dry rot in the floor. The survey did not open the floor and did not find dry rot there. No later decision about the sillwall was made, and this visit did not supply one.
Should every window sill be replaced because one is soft?
No. The note is one soft sill. The survey has not said the other sills are decayed, and firm frames elsewhere were not condemned with this one. What happens next for the othersills is outside this note and was not settled here.