Damp and moisture meters

Does Approved Document C mean an old house fails if a moisture meter reads high?

No. Approved Document C is guidance on meeting building regulations for site preparation and resistance to moisture, mainly when work is being built. It is not a pass mark for a surveyor’s meter, and it does not diagnose rising damp in a house that is already standing.

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?

Building regulations and a home survey answer different questions. The regulations, and the Approved Documents that support them, describe standards for building work. A RICS home survey describes the condition of what is there, from a visual inspection, with ratings where the level of survey uses them. A high reading is not a breach of Approved Document C, and a low reading is not approval under the regulations.

If you are buying a house with a new extension, you may also ask your solicitor for building-regulations paperwork. That paperwork is not the same document as the survey. The Property Care Association still expects a damp comment to be tied to a cause. Use Approved Document C as background for new work, not as a score written on the kitchen wall.

What should you ask your surveyor?

Are you quoting Approved Document C as a standard the whole house must already meet?
Is the damp comment about old fabric, or about a recent extension?
What would a building-control certificate cover that the survey does not?

What are the typical next steps?

Do not tell a seller the house is illegal because a meter beeped.
If an extension is new, ask the solicitor for the completion certificate as well as reading the survey.
Keep the damp investigation, if you need one, separate from the building-regulations question.

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

Does a completion certificate prove the walls are dry today?

No. It is about the work that was signed off, not about a leak that started afterwards.

Can a surveyor enforce Approved Document C?

No. Enforcement sits with the building-control body. The surveyor reports condition.