Non-standard construction
A builder has quoted cavity-wall insulation for a Wimpey no-fines house. Why is that quote using the wrong wall?
The quote is using the wrong wall because a Wimpey no-fines house is solid no-fines concrete, not a cavity wall that insulation is pumped into. Cavity-wall insulation assumes two leaves with a gap and, usually, ties. This system does not have that gap. The survey's job is to name the wall that is there. A builder's price for a cavity treatment does not create a cavity, and the home survey has not found one just because the quote says so.
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?
No-fines concrete was cast in situ as a solid wall, then usually rendered. People confuse it with cavity brick because both can look like a rendered semi from the pavement. The confusion matters: a cavity specification describes a different building. Injecting or filling a cavity that is not there is the wrong operation. The survey does not design that work and has not opened the concrete to invent a leaf the system does not have.
Show the survey's construction note to the builder and ask them to requote against no-fines concrete, in writing. Do not pass a cavity price to your solicitor or a lender as if the wall had been opened and found to be cavity brick. If someone still believes there is a cavity, they need evidence from an inspection that actually finds one. This report has not supplied that evidence.
What should you ask your surveyor?
- Did you see any cavity, or only solid no-fines concrete?
- What features made you name Wimpey no-fines rather than cavity brick?
- Are you saying a cavity-insulation quote does not match the wall you found?
What are the typical next steps?
- Tell the builder the wall is no-fines concrete, not a cavity.
- Do not treat the cavity quote as evidence of a cavity.
- Keep the survey's construction name ahead of the builder's specification.
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 render sounds hollow, is there a cavity after all?
Not from a hollow sound alone. Render can drum without a masonry cavity behind it. The house is named as Wimpey no-fines, which is solid concrete. The survey has not converted that into a cavity wall. A hollow sound is not a second leaf of brick.
Could cavity insulation still be a fair extra if the quote is cheap?
No. A low quote does not correct the wall type. The specification is for a cavity this house does not have. Ask for a description that matches no-fines concrete before you compare prices. A low price does not invent a cavity in no-fines concrete.