Windows, doors and glazing
Can single glazing put condensation on the glass without any damp-proof course having failed?
Yes. Single glass is cold. Moisture from cooking, bathing and breathing lands on it. That is condensation, not water rising from the ground. A home survey can point at the pattern. It does not measure humidity, and it should not turn misted morning glass into an instruction to inject the wall.
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?
The useful distinction is where the water sits. Beads on the pane, and mould on the cold frame, follow the glass. A tide mark at skirting level, with salts, is a different investigation. Both can exist in one room. The surveyor’s job is to say what they saw, not to sell a ventilator or a damp-proof course.
You do not have to replace single glazing before you buy. It is a thermal fact. When you do replace it, that work is often building regulations work in England, which is a solicitor’s and installer’s question. Approved Document F is why new windows tend to arrive with vents. None of that prices the glass. Ask a glazier if you want a figure for openings you have chosen to change.
What should you ask your surveyor?
- Is the comment about the glass, the reveal, or the wall at floor level?
- Did you see mould, or only condensation on a cold morning?
- Are you advising replacement, or only noting the glazing type?
What are the typical next steps?
- Do not treat single glazing as a rating 3 unless the report has said the frames have failed.
- Keep any later replacement on a building-regulations path. The survey will not notify it.
- If mould is on the wall rather than the glass, read the damp pages before you buy glass.
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 the same as a new sealed unit?
No. Secondary glazing is an extra pane inside the existing window. It can warm the room side. It does not replace the outer frame.
Will new double glazing by itself stop mould in a corner?
Not always. The corner may still be cold and unventilated. Glass is only one part of that pattern.