Damp and moisture meters
Daylight shows under a new door and the mat was wet. What weather path is the gap, separate from the wall damp-proof course?
The gap under the new door is a weather path for driven rain, separate from the wall damp-proof course. Daylight shows under the door and the mat was wet, so water is crossing at the threshold. That is not the same mechanism as moisture rising through the wall past a damp-proof course. The survey has recorded the gap and the wet mat. It has not blamed the wall barrier, and it has not shown that the course itself has failed.
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 new door can be hung with too much clearance, or the threshold bar can be missing, so rain lands on the mat even when the wall is doing its own job. Wet at floor level by the door is what that gap produces. It does not, by itself, mean the damp-proof course is bridged or broken. The survey did not lift the threshold to expose the course. The path it has named is the daylight under the door, not a failure of the wall.
Ask a joiner to close the gap with a proper threshold or by adjusting the door, and keep that job off any damp treatment of the wall. Tell the solicitor the wet mat lines up with daylight under a new door. Do not commission a chemical damp treatment because the mat was wet. The survey has not specified injection, and it has not said the wall course is missing.
What should you ask your surveyor?
- Is daylight under the new door the weather path to the wet mat?
- Has that path been kept separate from the wall damp-proof course?
- Was the course itself left unexposed and unblamed?
What are the typical next steps?
- Treat the gap as a threshold leak, not as failed wall damp-proofing.
- Ask a joiner to close the daylight under the door.
- Do not commission chemical damp treatment on the wet mat alone.
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 wall meter was high nearby, is the course the cause?
Not from this note. A high reading, if one was taken, would still sit beside a door with daylight under it and a wet mat. The weather path named here is the gap. The survey has not shown the damp-proof course has failed, and it has not specified a chemical treatment. Deal with the door before you rewrite the wall.
Will a new mat solve the gap?
No. A dry mat would only hide the water the gap is letting in. Daylight under the door is the path. Until the threshold is closed, rain can wet the next mat in the same way. The survey has not blamed the wall course, and a mat is not a repair of the gap.