Age and type of house
Should a later side addition on a 1930s semi be described as if it were the original cavity wall?
No. A single-storey addition on the old side drive can be a different build from the 1930s house. The survey should describe the addition’s walls and the original walls from what it could see of each. It should not copy a cavity comment onto a solid addition, or a crack in the addition onto the main house, unless it actually saw both.
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?
The junction is where these notes usually fail. The original wall may have a cavity, a damp-proof course and air bricks. The addition may be a single leaf, a different block, or a wall the surveyor could not identify under render. One moisture reading at the joint does not name both constructions. Ask which wall was which, and whether the roof of the addition was included or only the house.
Papers for the addition are a solicitor’s question. The survey’s job is condition and the construction it could see. A home survey does not decide a planning class for a side extension, and it does not prove the cavity of the main house continues through the new wall. If the joint is cracked or wet, that is the finding. Do not reword it as a defect of every elevation.
What should you ask your surveyor?
- Which walls are original, and which belong to the addition?
- Could you see a cavity in the addition, or only in the main house?
- Is the crack or the damp at the joint, or in the original wall?
What are the typical next steps?
- Keep the addition as its own element when you ask for quotes.
- Do not insulate or tie a wall the survey could not show was a cavity.
- Send missing papers to the solicitor without pretending they are a crack.
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 an empty cavity in the main house describe the side addition?
Only if the survey saw the same construction there. Otherwise they stay separate.
Is the flat roof of a side garage the house roof?
No. If the addition has its own roof, ask for that covering to be described on its own.