London Renovation Cost Calculator (2026)

Your estimated range

£45,000 – £53,000

Typical 2026 London range for this type of project. Estimates exclude VAT (20%), professional fees and premium extras — the exact figure depends on survey, specification and access.

What drives this price

• Roof shape and conversion type — a mansard rebuild costs far more than a rear dormer.
• An en-suite adds around £8,000–£12,000 — and usually the most value.
• Premium finishes add roughly £5,000–£15,000 to the build cost.
• Staircase position, structural steel and headroom drive the labour.
• Combining hip-to-gable with a rear dormer typically totals £55,000–£85,000.

• Glazing — standard bi-fold doors start around £3,500; premium slim-frame sliders can hit £12,000+.
• Ground conditions — clay soil or nearby trees can mean piled foundations at £15,000–£25,000+.
• Access — a mid-terrace with no side access can add 15–25% to labour costs.
• A new kitchen inside the extension is usually quoted separately.
• Planning route and Party Wall agreements add fees and lead time.

• Structural glass — a single large panel can cost £4,000–£8,000 before installation.
• Specialist engineering — structural glass design packages run £3,000–£8,000.
• Crane installation — a London crane day typically costs £2,000–£5,000.
• Solar-control glass and shading are essential to avoid summer overheating.
• Glass extensions almost always need full planning permission.

• Cabinetry tier — usually 35–45% of the whole budget.
• Worktop material — laminate from £800; marble up to £8,000.
• Appliances — from £2,000 budget suites to £15,000+ premium brands.
• Knocking through adds a steel beam, structural engineer and Building Control.
• Moving services (sink, gas, waste) adds first-fix plumbing and electrics.

• Moving the toilet or bath means re-routing pipework — the biggest single cost driver.
• Tiling runs £60–£250 per m² supplied and fitted in London.
• Sanitaryware — high-street to designer brands can be a five-figure difference.
• A wet room adds £1,000–£3,000 for full tanking and graded drainage.
• Period properties often hide failed plaster or old pipework behind the tiles.

• Existing cellar vs new dig — underpinned excavation costs two to three times more per m².
• Underpinning is often £35,000–£80,000 on its own for a new basement.
• Full dig-outs rarely finish under £150,000 all-in once underpinning, waterproofing and fit-out are counted — most London projects land between £150,000 and £400,000+.
• BS 8102 waterproofing with a pumped sump typically runs £12,000–£25,000.
• Party Wall surveys cost roughly £1,000–£2,000 per neighbour.
• Lightwells add £5,500–£15,000 but transform natural light.

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