Damp and moisture meters
A new door threshold bridges the damp-proof course and the plaster beside the frame is marked. What path is that threshold, as against a failed window elsewhere?
The new door threshold is a bridge across the damp-proof course, and that is the path to the marked plaster beside the frame. It is not a failed window elsewhere. Moisture can track over the course where the threshold crosses it and show in the plaster next to the lining. The survey can see the threshold and the marking. It has not blamed another window, and it has not laboratory-tested the wall. The path to name is this threshold at this door, not a glazing failure in a different opening.
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?
A damp-proof course is meant to break the path from wet masonry below to the wall above. A new threshold, a ramp or a raised path that crosses that line joins the two again. Plaster touching the bridge can take the moisture and show a mark beside the frame. That is local to the door. A failed window is a different opening, with its own frame, sill and glass. The survey should not drag this mark across the house to a window it has not linked.
A builder can alter the threshold so it no longer crosses the course, and can say whether the plaster needs to be cut back. That is a detail at this door. Tell the solicitor the marking is being read with the new threshold, so a seller explanation about an old window should not be accepted as the cause unless the survey actually tied the mark to that window. It has not.
What should you ask your surveyor?
- Where does the new threshold cross the damp-proof course?
- Is the plaster mark immediately beside this frame?
- Have you separated this path from any window you did not link?
What are the typical next steps?
- Name the threshold bridge as the path to the marked plaster.
- Do not blame a failed window that was not linked.
- Ask a builder to break the bridge at this door.
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
If the plaster mark is small, is the bridge still the path?
Yes. The size of the mark does not change the geometry. A threshold that crosses the damp-proof course is still a bridge. A small mark may mean less decoration is affected. It does not make the path a window somewhere else.
Could the mark be old paint rather than moisture?
It could be decoration, and the survey has not laboratory-tested the plaster. What it has seen is a mark beside a bridging threshold. The path to investigate is that threshold. Calling it a failed window would still be the wrong opening.