Damp and moisture meters
Why can a window reveal be wet after rain when the skirting below is dry?
Because the water is arriving at the opening, not from the ground. A failed seal, a cracked sill, a missing cavity tray or driving rain at the frame can wet the reveal and leave the skirting dry. That is penetrating damp at the window. It is not proof the damp-proof course has failed. A home survey sees the day it visits. It may not see the rain.
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?
Cavity trays and closers are there so water that gets into a cavity is thrown out above the opening. A visual survey often cannot see the tray. It can see a stain that starts at the head or the jamb and a dry wall below. The Property Care Association’s distinction still applies: name the path. Government damp guidance does not call every window stain rising damp.
A window fitter and a damp diagnosis are different jobs. Missing paperwork for replacement windows is not, by itself, the leak. Ask what was wet and what was dry. There is no RICS price for a new tray or a new window. Quote the opening that is actually staining, not the whole elevation.
What should you ask your surveyor?
- Is the staining at the reveal, the head, or the skirting?
- Did you see a defective sill or frame, or only the internal mark?
- Are you separating this from damp at ground level?
What are the typical next steps?
- Watch the opening in rain if you still have access, and photograph it.
- Do not buy a damp-proof course for a wet window head.
- Ask a competent window or building contractor about the opening the survey described.
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 misted double-glazed unit the same defect?
No. A misted unit is a failed seal in the glass. It is not a wet reveal, though both can be present.
Does dry weather on survey day clear the window?
No. A dry day means it was dry then. It does not prove the reveal stays dry in rain.