Cost guide · 2026
LoftConversionCostinLondon2026
Comprehensive 2026 pricing for every type of London loft conversion. Real costs from 200+ completed projects, broken down by configuration, finish spec and zone.
Quick answer
A loft conversion in London costs £45,000–£145,000 in 2025–2026. A Velux (rooflight-only) conversion starts from £45,000; a standard dormer £60,000–£90,000; a hip-to-gable with dormer £75,000–£110,000; an L-shape dormer £80,000–£120,000; a full mansard £95,000–£145,000. Cost per m² typically runs £2,200–£3,400. All Builderr quotes are fixed-price with no provisional sums.
What moves the price
The seven cost factors that matter most.
Velux £45k–£65k; dormer £60k–£90k; mansard £95k–£145k. Type dominates the budget.
Lofts below 2.4m ridge height need a mansard; existing 1970s+ trussed roofs need full structural redo (+£15–25k).
Bathroom add £8,000–£15,000 including tanking, sanitaryware, UFH.
Each Velux £700–£1,400 installed; each dormer cheek window £900–£1,800; juliet balcony £2,200–£4,500.
Standard winder over existing stair £4,500–£7,500; bespoke open-tread feature stair £9,000–£18,000.
Permitted development +£2,500 fees; full planning (mansards, conservation) +£6,500 fees + 8–12 weeks.
Conservation often forces traditional materials and slim glazing (+£4–8k) and front dormer restrictions.
Cost breakdown
Where the money actually goes.
Percentage breakdown of a typical mid-spec project. Add or subtract per your finish tier.
| Line item | % of total | £ on avg project |
|---|---|---|
| Structure (steels, floor, roof) | 11% | £10,450 |
| Insulation & weatherproofing | 9% | £8,550 |
| Windows & glazing | 7% | £6,650 |
| First fix MEP | 11% | £10,450 |
| Plaster & decoration | 8% | £7,600 |
| Stairs & joinery | 8% | £7,600 |
| Bathroom (if ensuite) | 7% | £6,650 |
| Flooring & finishes | 5% | £4,750 |
| Lighting & second fix | 4% | £3,800 |
| Fees & approvals | 11% | £10,450 |
| Site management & plant | 11% | £10,450 |
| Margin & contingency | 8% | £7,600 |
Real projects
Worked examples from completed builds.
London zones
Where your borough sits in the price band.
| Zone | Multiplier | Notes |
|---|---|---|
| Zone 1 (W1, SW1, NW1, EC, WC) | 1.18–1.25× | Conservation, listed, parking and access surcharges |
| Zone 2 (NW3, SW3, SW10, N1, E1, E2) | 1.10–1.15× | Premium areas, mostly conservation |
| Zone 3 (SW6, W6, NW5, N16, E5, E8) | 1.00–1.08× | Baseline London pricing |
| Zone 4 (SW17, W7, N8, E11, SE13) | 0.95–1.00× | Slightly below baseline |
| Zone 5–6 (Outer boroughs) | 0.88–0.95× | Easier access, lower trade rates |
Builderr vs other London builders.
The construction industry has a wide distribution of operators. Here's what changes between a directly-employed, fixed-scope outfit and the alternatives.
| Criterion | Builderr | Typical London builder | Cowboy outfit |
|---|---|---|---|
| Labour model | Directly employed team (PAYE) | Mixed subcontract gangs | Day-rate cash labour |
| Pricing | Fixed-scope itemised quote | Estimate + provisional sums | Verbal price + variations |
| Design & engineering | In-house architect + SE | Outsourced, separate billing | Builder draws on the back of an envelope |
| Planning + LDC handled | Yes — included in price | Often charged extra | Builder asks you to apply |
| Party wall surveyors | Instructed by us | Your responsibility | Skipped (illegal) |
| Building control | Plans + site inspections booked by us | Building Notice route | Not registered |
| Project management | Dedicated PM, weekly photo updates | Foreman doubles up | Owner-manager juggles 5 jobs |
| Payment schedule | Stage payments against signed-off milestones | Weekly invoices | Cash up front |
| Insurance | £10M PL + 10yr structural warranty | £2–5M PL only | No documented cover |
| Snags at handover | <3 typical | 20–30 typical | Walk-off mid-job common |
| Variation creep | 0% — fixed scope | +15–25% over original quote | +40%+ regularly |
Save £19,000–£42,750 on a loft conversions.
Industry data (FMB, RICS, Which? Trusted Trader 2024) shows the average London construction project overruns by 18–22% on cost and 25–35% on time. Fixed-scope contracts with a single accountable team eliminate that variance. The savings above assume a typical project at £95,000.
Related
See the full loft conversions service page.
Guides & insights
FAQ
Loft Conversion Cost in London:
common questions.
How much does a loft conversion cost in London in 2025?
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In 2025, a Velux loft conversion starts from £45,000; a standard rear dormer runs £60,000–£90,000; a hip-to-gable with dormer £75,000–£110,000; an L-shape dormer £80,000–£120,000; a full mansard £95,000–£145,000. Cost per m² is £2,200–£3,400. Inner London adds a 10–25% zone uplift.
What is the cheapest type of loft conversion?
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A Velux (rooflight-only) loft conversion is the cheapest, starting from £45,000. It keeps the existing roofline and adds rooflights only — no dormer structure, no planning application in most cases. Headroom is limited to the existing ridge height, which makes it unsuitable for many London terraces with low ridges.
Why do loft conversions cost so much in London?
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London loft conversion costs are higher than the national average due to: higher trade rates (London premium 15–30% above national average), conservation area and planning compliance costs, party wall surveyor fees, difficult access and parking on London streets, and the complexity of working on Victorian and Edwardian roofs with varying structural conditions. London loft conversions also typically include ensuite bathrooms and high-spec finishes that raise costs.
Does a loft conversion cost include VAT?
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Most loft conversion builders quote ex-VAT. VAT is charged at 20% on residential construction works for buildings that have been in residential use for more than 2 years. However, if you are converting a property that was previously non-residential, or if you are a disabled person making adaptations, reduced or zero VAT rates may apply. Builderr's quotes always state clearly whether VAT is included.
How much does it cost to add an ensuite to a loft conversion?
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Adding an ensuite to a loft conversion typically costs £8,000–£15,000, depending on size, finish and whether plumbing needs to be extended from below. A compact 4m² ensuite with shower, WC, basin and underfloor heating: £8,000–£12,000. A larger ensuite with freestanding bath, walk-in shower and premium tiling: £15,000–£25,000.
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