Age and type of house
The main walls are cavity brick and the bay is solid. Why should a damp reading in the bay not be copied onto the cavity walls?
Because the bay is a different wall. The main walls are cavity brick and the bay is solid, so a damp reading in the bay belongs to that solid construction. The survey has recorded the reading where it was taken. It has not shown the same condition in the cavity walls, and it has not tested them by copying a number across. A solid bay is one leaf, often more exposed and without the cavity that separates the main inner leaf from the rain. The cavity walls are the other construction. Copying the bay onto them invents a finding the inspection did not make.
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?
Nineteen-thirties bays were frequently built solid while the flanks and the rear went up as cavity work. Rain on a solid bay can reach the inner plaster directly. Rain on a cavity wall has a gap to cross, and damp there is a different path: a bridge, a tray, a tie line. A moisture meter on the bay plaster reads that bay. It does not read the cavity, the far elevation or the inner leaf of a wall the meter was not held on.
Ask the surveyor to say the reading was in the solid bay and not in the cavity walls. Tell the solicitor not to describe the house as damp throughout on the back of the bay. Do not accept a treatment quote that prices every elevation from one solid projection. If the bay needs work, it is the bay: its construction, its joints and its exposure. The cavity walls stay as the survey actually found them, which was not this reading.
What should you ask your surveyor?
- Was the damp reading taken on the solid bay, not on the cavity walls?
- Did you see a separate damp path in the cavity brick at all?
- Will the report keep the bay finding off the main walls?
What are the typical next steps?
- Keep the damp reading on the solid bay.
- Do not copy it onto the cavity walls.
- Price any follow-up for the bay alone unless the survey named more.
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 bay and the main wall share a room, does the reading travel?
Only if it was found on both. Sharing a room does not make two constructions one wall. The survey's reading stays on the solid bay until someone actually records damp in the cavity walls, which this note has not done.
Does a dry cavity wall nearby clear the bay?
No. Dry cavity brick is the other construction behaving differently, which is the point. It does not clear the solid bay, and it does not let the bay's reading be painted back onto it. That is as far as the recorded facts about the solid-bay reading can be taken.