Damp and moisture meters
Does mould on a window board prove the wall below has rising damp?
No. Mould on a window board is usually condensation on a cold ledge under the glass. It does not prove that the wall beneath the board has rising damp. Check whether the skirtings and the plaster under the window are wet, or whether only the board and the glass edge are affected.
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 boards sit under cold glass. Night air cools the glass and the board, and room moisture grows mould along the back edge, especially behind curtains. That growth can be heavy while the wall below the board stays at ordinary dryness. Rising damp would be looked for at the base of the wall, not assumed from a mouldy sill. A surveyor can see the board. They are not obliged to cut into the wall under it to mention the mould.
A visual survey does not lift the board and does not guarantee the concealed plaster. If the plaster under the window is stained after rain, that may be the reveal or the cill letting water in, which is a different mechanism from both the mould and from rising damp. Keep the three apart in anything you ask the seller to address. Wiping the board does not change the cold glass or a failed cill.
What should you ask your surveyor?
- Is the mould only on the board, or is the plaster below it stained?
- Are the skirtings under this window dry?
- Did the growth sit behind curtains or a blind?
What are the typical next steps?
- Do not treat the wall for rising damp because the window board is mouldy.
- Note whether the glass itself is wet in the morning.
- If the plaster under the window stains after rain, ask about the cill and the reveal, not the damp-proof course.
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
Is a timber window board rotten if it has mould?
Not automatically. Mould is growth on the surface. Soft, crumbling timber is decay, and it needs a separate look.
Does double glazing stop this?
It can warm the glass. It does not help if the room's moisture has no way out, or if the new cill is trapping water.