Damp and moisture meters
The seller says a solid floor replaced a rotten timber floor. What can the survey not check about the damp-proof membrane under that new slab?
The survey cannot check the damp-proof membrane under that new slab, because the membrane, if it exists, is buried in the floor. The seller's account, that a solid floor replaced a rotten timber floor, is a statement the inspection cannot verify from the surface. The survey has not seen the membrane, has not seen whether it is continuous, and has not seen whether the old rotten timber was fully removed. A reading on the finished floor is not a view of the layer underneath. The membrane remains unchecked.
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 membrane only works if it is there, continuous, and lapped to the wall damp course in the way the floor was designed. None of those junctions is visible once screed or finish is down. The seller may be right, partly right, or describing a slab that went in with no membrane at all. The survey can note what the surface looks like and what it was told. It cannot excavate the floor to prove what was said.
Ask the solicitor for any invoices, guarantees or building papers for the new floor, and treat them as documents, not as a substitute for the missing view. Tell them the home survey has not confirmed a membrane. The survey has not said the floor is damp and has not said it is dry at depth. If the surface is suspect, a damp specialist can advise whether any further opening is justified. Do not take up the slab on a viewing.
What should you ask your surveyor?
- Did you record the seller's account without seeing the membrane?
- What, if anything, could you actually inspect of the solid floor?
- Have you left the membrane itself unchecked?
What are the typical next steps?
- Do not treat the seller's account as proof of a damp-proof membrane.
- Ask the solicitor for papers on how the solid floor was built.
- Keep the buried membrane as something the survey could not check.
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 floor feels dry, has the membrane been confirmed?
A dry-feeling surface does not show a membrane. The survey still has not seen under the slab, so the seller's account of the membrane remains unchecked whatever the surface feels like. Asking about it again later still leaves this dryslab point outside what the survey decided.
Can a moisture meter on the screed see the membrane?
No. A meter, if one was used on the surface, is not a view of a buried sheet and is not a laboratory test of the floor. The survey cannot check the membrane from above. The home survey itself did not pursue this meterface question any further than the visit.