Basements and cellars
What should you ask if a basement was dug out after the house was built?
Ask who designed the structure and which building-regulations approval exists. Digging out a cellar changes foundations, retaining walls and moisture. A home survey sees cracks, tanking and a stair. It does not recalculate the underpinning, and it does not phone building control for you.
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?
GOV.UK explains that building work needs approval by a council, a private inspector, or a competent-person route where one exists. Underpinning and a new retaining wall are not a window replacement. The papers should match the scale of the hole. A missing letter is the solicitor’s chase. Movement in the walls above is the surveyor’s comment.
Do not assume a guarantee company’s leaflet is approval. If the rating on the structure is 3, RICS’s Level 3 wording expects written quotations or investigation before legal commitment. An engineer’s look is that investigation. This page states no underpinning price.
What should you ask your surveyor?
- What signs of movement did you see above the dug-out area?
- Could you see how the walls are held, or only the lining?
- Which papers do you want the solicitor to obtain?
What are the typical next steps?
- Get the approval papers and any engineer’s calculations if they exist.
- If the structure is unclear and you need it clear, instruct an engineer. Do not invent a figure.
- Do not dig further as “due diligence” before you own the house.
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
Is a cellar that was always there the same question?
No. An original cellar is not a retrospective dig. It can still be damp. The paperwork question is about later structural work.
Does a party-wall award replace building regulations for a basement?
No. GOV.UK treats them as separate where both apply.