Damp and moisture meters
Can moisture trapped between secondary glazing and the original sash be nothing to do with the damp-proof course?
Yes, condensation can sit in the gap between secondary glazing and the original sash when that gap is cold and the room is humid. That is a glazing problem, not proof the wall or the damp-proof course has failed. The survey sees the glass and does not take the secondary panel off.
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?
Secondary glazing is an extra pane or panel on the room side of the existing window. It is not a replacement window. If the gap is not ventilated, or moist room air leaks into it, water beads on the old glass and can run onto the staff bead and the sash. Timber then stains in a way that looks like the wall is wet. The plaster around a dry reveal can be untouched. Rising damp is not water trapped in a glazing gap. A surveyor should say the moisture is in the gap if that is what they could see.
A home survey does not dismantle secondary glazing and does not test the seals. Misted factory-sealed units are a different product again. Do not inject the wall because the sash gap is wet, and do not assume the original window has failed as a frame just because the gap mists. Note whether the sash timber is soft or only surface-wet. Soft timber is a window repair. Beads on the glass are ventilation of that gap, and of the room.
What should you ask your surveyor?
- Is the water between the secondary panel and the sash, or on the room face?
- Is the sash timber soft, or only the glass wet?
- Is the wall below the window dry?
What are the typical next steps?
- Do not treat trapped condensation in the glazing gap as rising damp.
- Do not remove secondary glazing on a viewing. Ask the surveyor what they could see without that.
- If the sash is soft, that is a window repair, still separate from 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 secondary glazing a failed sealed unit?
No. A sealed unit mists between its own two panes. Secondary glazing is a separate panel. The water is in a different gap.
Can the original single glass mist with no secondary panel at all?
Yes. Cold single glass condenses room moisture. That, too, is not the damp-proof course.