How much does a basement conversion cost in the UK?
Basement conversion costs £10,000 to £150,000 in the UK, typically around £50,000 for the project. What moves the price most is converting an existing cellar versus digging a new basement, so a simpler job sits near the bottom of that range and a larger or higher-spec one near the top. Prices reviewed June 2026.
Converting a basement ranges from tidying up an existing dry cellar to digging out a new basement under the house. Waterproofing and structural work drive most of the cost.
Basement conversion cost calculator
Use the calculator to price your basement conversion in 2026. Adjust the options and area for a UK cost range. Nothing is sent anywhere.
Basement conversion cost breakdown
Typical basement conversion costs, by option:
| Type | Typical UK cost |
|---|---|
| Convert an existing dry cellar | £10,000 to £30,000 |
| Lower the floor and tank the cellar | £30,000 to £70,000 |
| Dig out a new basement | £70,000 to £150,000 |
| + Structural engineer and party wall | add £3,000 to £10,000 |
| + Full waterproofing / tanking | add £5,000 to £20,000 |
What's included in the price?
Typical basement conversion prices include:
- Structural and waterproofing work
- Floor, walls and ceiling
- Electrics, heating and lighting
- Building control sign-off
What changes the price?
The things that move basement conversion prices most:
Converting an existing cellar versus digging a new basement
Head height and whether the floor is lowered
Waterproofing and tanking
Structural engineer and party wall agreements
Does where you live change the cost?
In London, basement conversion typically costs around £65,000 for the project, about 30% above the UK average of £50,000. In the North, Scotland and Wales the guide figure is nearer £46,000.
| Region | From | Typical | Up to |
|---|---|---|---|
| Midlands / East (UK average) | £10,000 | £50,000 | £150,000 |
| London | £13,000 | £65,000 | £195,000 |
| South East / South West | £11,500 | £57,500 | £172,500 |
| North / Scotland / Wales | £9,200 | £46,000 | £138,000 |
Guide prices for the project, scaled with the same regional multipliers as the calculator. Not quotes.
Basement conversion cost in major UK cities
| City | From | Typical | Up to |
|---|---|---|---|
| Belfast | £8,500 | £42,500 | £127,500 |
| Birmingham | £9,800 | £49,000 | £147,000 |
| Bristol | £11,000 | £55,000 | £165,000 |
| Cardiff | £9,400 | £47,000 | £141,000 |
| Edinburgh | £9,800 | £49,000 | £147,000 |
| Glasgow | £9,000 | £45,000 | £135,000 |
| Leeds | £9,300 | £46,500 | £139,500 |
| Liverpool | £9,200 | £46,000 | £138,000 |
| London | £13,000 | £65,000 | £195,000 |
| Manchester | £9,600 | £48,000 | £144,000 |
| Newcastle | £9,000 | £45,000 | £135,000 |
| Sheffield | £9,200 | £46,000 | £138,000 |
City guide estimates, scaled by local labour costs. Indicative averages for basement conversion, not quotes.
London and the South East run well above the national figures, which is where most basement digs happen.
Common questions
How much does a basement conversion cost?
A basement conversion costs roughly £10,000 to £150,000 in the UK, typically around £50,000. Converting an existing dry cellar with good head height is £10,000 to £30,000, lowering the floor and tanking an existing cellar £30,000 to £70,000, and digging out a brand-new basement under the house £70,000 to £150,000. Structural, party wall and waterproofing work make up much of that.
Is a basement conversion worth it?
In high-value areas where you cannot extend outwards, a basement can add a lot of usable space and value, which is why they are common in London. Elsewhere the sums are harder, because digging out is expensive per square metre compared with a loft or an extension. Converting an existing dry cellar is far better value than a full dig-out, so the answer depends heavily on what you are starting with.
Do you need planning permission to convert a cellar?
Converting an existing cellar into a room usually falls under permitted development and does not need planning permission, though it does need building regulations approval for things like fire escape, ventilation and waterproofing. Digging out a new basement, or adding a light well or separate entrance, is more likely to need planning permission, especially in a conservation area, so check before starting.
Do basement conversions add value?
A well-done basement conversion adds living space, and in the right area it can add more value than it costs, particularly a self-contained or income-generating space. But the cost of a full dig-out is high, so the value uplift is far more reliable when you are converting an existing cellar than when you are excavating a new one. Get local advice on what the space is actually worth before committing.
Does a basement need tanking?
Yes. Below-ground rooms have to be properly waterproofed, usually with a tanking system or a cavity drainage membrane, because ground water will otherwise find its way in. This is one of the biggest costs and the one to never economise on, since a leaking basement is expensive and disruptive to fix. A specialist should design the waterproofing to a recognised standard.
Can I convert a basement myself?
You can do fit-out work like studwork, decorating and flooring, but the parts that decide whether a basement works are jobs for professionals. Waterproofing or tanking, and any lowering of the floor or structural change, need proper design and building control sign-off. Converting a dry cellar is £10,000 to £30,000, while lowering the floor or digging out runs £30,000 to £150,000. Get the tanking wrong and a damp basement is expensive to put right.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.