PRICE GUIDE · TRADES & CONSTRUCTION · 2026–2027
Basement Conversion cost in the UK
£30,000–£140,000 per project. Typically £75,000.
A basement conversion in the UK costs £30,000–£140,000, with £75,000 typical for turning an existing dry cellar into living space. Digging out a new basement or lowering the floor, which needs underpinning, is what pushes a project towards the top figure.
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HOW MUCH IT COSTS
How much does basement conversion cost in the UK?
| Low end | £30,000 | an existing dry cellar fitted out, outside London |
|---|---|---|
| Typical | £75,000 | what most people pay |
| High end | £140,000 | a new basement dug out and underpinned, in London |
Locufy guide prices for 2026–2027. Updated 2026. A national range, not a quote — enter your town above for real prices from the builders and trades near you.
What moves the price
- Existing cellar or new dig — converting a cellar with good head height costs far less than excavating a new basement
- Lowering the floor — gaining head height means underpinning the walls, the single biggest structural cost in a basement
- Waterproofing system — a cavity drain membrane with a sump and pump keeps groundwater out of the converted space
- Light and access — a lightwell, new windows or an external stair add to the basement conversion bill
- Ground conditions and party walls — clay, a high water table or shared walls in a terrace add engineering and surveyor costs
- London sites — tight access, muck-away and parking suspensions make basement work there the dearest in the UK
Building and repair prices in the UK are up 6% over five years (ONS Consumer Price Inflation, Services for maintenance and repair, to 2026 August). Five years ago a typical basement conversion would have cost about £66290 — an estimate from today's guide price and that index, not a recorded price. Source: ONS MM23 D7DO →
WHAT YOU GET
What a basement conversion booking includes
Takes: Eight to sixteen weeks for most basement conversions, longer for a full excavation. Not included: Party wall surveyor fees, planning application fees, kitchen or bathroom fittings and furniture are usually priced separately — see the related guides below.
WHAT PEOPLE BOOK
Common basement conversion jobs
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Basement Conversion near you, with prices shown
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How to pay less
- Convert the cellar you already have rather than digging deeper, if the head height is close to what building regulations need
- Get the basement waterproofing designed properly first, as fixing a leaking conversion later costs far more than doing it once
- Keep the basement layout simple, with plumbing near existing drains so a pump is not needed for every fitting
Before you book
- Building regulations approval is needed for a basement conversion, covering fire escape, ventilation, insulation and structure
- Check with the council whether your basement needs planning permission, which is common for new excavations and lightwells
- Serve party wall notices on your neighbours before any digging near a shared wall, as the Party Wall Act requires
- Tell your home insurer about the basement works before they start, as structural work can affect your cover
Basement Conversion cost: questions people ask
£30,000–£140,000 per project, with £75,000 typical. Fitting out an existing dry cellar is the cheapest route; excavating a new basement with underpinning reaches the high figure.
Eight to sixteen weeks for most projects. A full excavation or a lowered floor with underpinning can take several months.
Converting an existing cellar into living space is often allowed without it, but digging a new basement, adding a lightwell or changing the front of the house usually needs planning permission. Building regulations approval is needed either way.
If you are digging near a shared wall or foundations, the Party Wall Act means you must serve notice, and a surveyor may need to agree an award before work starts.
Party wall surveyor and planning fees, kitchen or bathroom fittings, furniture and decoration are generally extra.
They are Locufy guide prices for the UK, assembled from published UK basement conversion cost guides — a national range, not a quote. The ground, the structure and the access set your real cost.