Damp and moisture meters
Do secondary glazing, together with an unvented sash box, count as evidence on condensation trapped in the cavity between the glasses, or only as a note of what was visible?
They are only a note of what was visible, not evidence of condensation trapped between the glasses. Secondary glazing is an extra pane or frame set inside the sash. An unvented sash box means the frame or the space was recorded without a vent. The survey saw those two things. It did not open the cavity between the glasses, did not wipe it as a test, and has not decided that condensation is trapped there. No humidity was measured.
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 leaves a narrow space in front of the original glass. If that space is sealed and the room is moist, condensation can form, but this visit did not record water between the panes. An unvented sash box is a separate air path that is closed. The report pairs the two. It did not remove the secondary frame, and it did not blame the box for anything on the glass.
Tell the solicitor the secondary glazing and the unvented box were described, and that trapped condensation was not shown. If the panes mist, a glazing fitter can look at ventilation of the cavity as a separate job. The home survey has not designed that. The lender has no condensation test. Do not remove the secondary glazing on the strength of this note alone. The cavity between the glasses stays uninspected.
What should you ask your surveyor?
- Was the cavity between the glasses left unopened?
- Did you note an unvented sash box without measuring moisture?
- Have you avoided calling trapped condensation a result?
What are the typical next steps?
- Treat the secondary glazing and the box as a visual note.
- Ask a glazier about the cavity only if misting is actually seen.
- Tell the solicitor condensation between the glasses was not shown.
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
Does secondary glazing always mist if the box is unvented?
The survey has not said so. An unvented box and a secondary pane are two notes. Misting depends on how moist the room is and how the gap is sealed, and neither was measured. The report does not turn the pairing into a forecast of trapped condensation.
If the main sash glass is clear, is the cavity proved dry?
No. Clear glass on the day of the visit is one look. Condensation comes and goes. The cavity was not opened and was not wiped as a test. A clear face does not describe the space between the glasses. The note stays visual.