Windows, doors and glazing
The sill of a bay window is rotten and the sashes above it still open. What timber has the survey actually called decayed?
The timber the survey has called decayed is the sill of the bay, not the sashes above it. Those sashes still open. The inspection can describe softness, a broken paint line or lost section in that sill where it was seen. It has not called the whole bay rotten, and it has not opened hidden ends of the frame to chase decay that was not exposed. The named timber is the sill. The sashes are a separate piece that still worked on the day.
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?
Bay sills sit in the weather and fail first, while the sliding or hinged sashes above can still move. Decay in the sill is a loss of that horizontal timber, often where paint has split and water has sat. The survey names what it could probe or see. It does not, by naming the sill, declare the jambs, the head or the sash stiles decayed. Those pieces need their own sentence. Opening them was not part of calling the sill rotten.
A joiner should price a sill repair and say, once the rotten timber is cut back, whether the decay runs into the frame. That discovery is future work, not a finding already made. Tell the solicitor the decayed element is the bay sill. If a seller quote replaces the entire bay, compare it with the sill the survey actually called. Do not let the sashes, which still open, be written up as rotten by association.
What should you ask your surveyor?
- Which piece of timber did you call decayed: the sill alone?
- Did the sashes above still open, and were they separately described?
- How far did you test beyond the visible soft timber?
What are the typical next steps?
- Limit the decay note to the bay sill that was seen.
- Do not extend that note to sashes that still open.
- Ask a joiner whether the rot runs past the sill once it is opened.
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 a rotten sill still feed water into the frame while the sashes open?
It can. A failed sill is a shelf that holds water against the bottom of the frame. The survey has not followed that water into hidden timber. The sashes opening shows they still move. It does not prove the frame ends behind the sill are sound.
Is flaking paint on the sill the same thing as the decay?
No. Flaking paint is a coating failure. The survey has called the sill decayed, which is lost or soft timber, not paint alone. Paint can sit beside decay. The finding to use is the rotten sill, not the decoration on the bay.