Damp and moisture meters
A perpend is missing on the weather face and a damp patch inside lines up with it after rain. Why should that be read as a rain path before any rising-damp treatment?
Read it as a rain path first, because a missing perpend on the weather face lines up with a damp patch inside after rain. An open cross joint is a hole in the face that rain can use. The alignment after rain is the timing that fits water coming through, not water rising from the ground. The survey has recorded the missing joint and the matching patch. It has not established rising damp, and it has not justified a rising-damp treatment. The rain path is the reading that matches what was seen.
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?
Rising-damp treatments are aimed at moisture from the ground. They are a poor answer to a hole in the outer leaf that lines up with a wet patch when it rains. Filling the perpend, and checking the joint around it, deals with the path in front of you. Injecting a wall while the joint stays open leaves the rain route in place. The survey did not test a chemical damp-proof course and did not diagnose rising damp by a meter alone.
Ask a bricklayer or a damp specialist to deal with the missing perpend as a rain path, and to say whether anything further is even relevant once that joint is understood. Tell the solicitor the survey has not recommended a rising-damp treatment on this evidence. Do not accept a quote for injection that ignores the open joint. The patch should be read against the hole that lines up with it.
What should you ask your surveyor?
- Does the internal patch line up with the missing perpend?
- Was the patch related to rain rather than to a proved rising damp?
- Have you kept rising-damp treatment off this evidence?
What are the typical next steps?
- Read the missing perpend as the rain path.
- Do not start from a rising-damp treatment.
- Have the open joint assessed before any injection is discussed.
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 a meter reads high, does that overturn the rain path?
A high meter reading shows a wet wall. It does not name the source. The missing perpend lines up with the patch after rain, which is why the rain path comes first. The survey has not established rising damp. A meter does not close an open joint.
Could both rain and ground moisture be present?
They could, but the note you have is the joint and the patch after rain. That is a rain path, and it should be read before any rising-damp treatment. The survey has not proved a second mechanism. Deal with the hole that was seen before inventing another cause.