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Converting a Basement: the FAQs

Some homes have existing cellars that can be converted, but you can create a new basement with the right expertise and approvals.

Q: Do we need any approvals?

A: Converting an existing cellar to a habitable space involves only a change of use and so does not require planning permission. Reducing the floor level of a cellar or creating a new basement will enlarge the volume of your home and is therefore treated as an extension, so may need planning permission. Either way, you should always check with your local authority whether or not planning permission is required.

The creation of new lower ground floor living space will, however, require Building Regulations approval. The renovation of an existing habitable basement, or the repair of a cellar that does not involve a change of use is excluded. Visit for advice.

Q: How long will it take?

A: Converting a single-room cellar using a membrane lining system can take just two or three weeks, including digging out the sump and fitting the pumping system. Find out more about the conversion process.

Q: How much will it cost?

If you have an existing cellar with enough headroom, this can be fairly easily converted from around £750/m². However, when floor levels need lowering, drains diverting, underpinning is needed or a whole new basement needs excavating, the costs will sharply rise. Your can read more about the associated costs in our guide to converting a basement.

Q: How do we find a builder?

A: Choose a specialist contractor with experience of the waterproofing system you have chosen. Search the website of The Basement Information Centre ( for a company registered with the British Structural Waterproofing Association. Look for an insurance-backed guarantee that will pay for repair works even if the contractor goes out of business.

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