Loft Conversion Cost in London 2026: The Complete Guide
Loft conversion costs in London for 2026: Velux £35k–£60k, dormer £55k–£95k, mansard £80k–£140k. Real prices, planning notes and what moves the final bill.
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A loft conversion in London costs £35,000–£60,000 for a Velux, £55,000–£95,000 for a dormer and £80,000–£140,000 for a mansard in 2026. Which of the three your roof can take is decided by head height and structure long before budget comes into it — our loft conversion service page sets out the four types, the cost hub breaks the figures down by area, and the estimator puts a band on your own roof in about two minutes.
A loft conversion is the most cost-effective way to add a bedroom and bathroom to a London property. Done well, it adds more value than it costs — and in prime postcodes, the uplift can be substantial.
This guide sets out real 2026 costs from 2VP’s completed projects in Fulham, Chelsea, Battersea and across West London.
Loft Conversion Costs at a Glance (London 2026)
| Conversion Type | Typical London Cost | Notes |
|---|---|---|
| Velux (roof lights only) | £35,000 – £60,000 | No external change, PD rights |
| Rear dormer | £55,000 – £95,000 | Most common; adds a bedroom + en suite |
| L-shaped dormer | £70,000 – £115,000 | Rear + side; good for corner plots |
| Hip-to-gable | £65,000 – £105,000 | Semi-detached or detached homes |
| Mansard (rear) | £80,000 – £140,000 | Maximum volume; requires full planning |
| Full mansard (front + rear) | £120,000 – £180,000 | Most disruptive, maximum value uplift |
Prices include design, structural engineering, building regulations, labour, materials and VAT.
What Drives the Cost?
1. Conversion type
The structural complexity is the primary cost driver. A Velux conversion uses the existing roof structure — it’s essentially a fit-out. A mansard removes and rebuilds the entire rear slope in brick or render, which is a fundamentally different project.
2. Postcode
London is not one market. A dormer conversion in Chelsea (SW3) or Notting Hill (W11) costs 30–40% more than the same work in outer boroughs — partly because of labour rates, partly because conservation area requirements add architect and planning consultant fees, and partly because the material specification expected by those postcodes is higher.
2VP operates mainly in prime and inner London (SW6, SW3, SW11, W11, W4, W6, W2) where our rates reflect the quality those postcodes require.
3. Specification and finish
The biggest variable within any conversion type is what you put inside: en-suite bathroom specification, custom joinery for eaves storage, engineered oak floors vs. carpet. The difference between a “minimalist” and a “signature” finish on a standard dormer can be £25,000–£35,000.
4. Structural conditions
Party wall agreements (required when you work adjacent to a neighbour’s wall), steel beam sizing, and any hidden structural issues discovered during opening-up all affect the final cost. We include a contingency in every JCT contract to handle what the survey couldn’t see.
5. Planning and conservation area requirements
Properties in Article 4 Direction areas — most of Chelsea, Notting Hill, parts of Fulham and Westminster — cannot use Permitted Development for roof alterations. A Full Planning Application adds £3,000–£8,000 in fees and 8–12 weeks to the programme.
Dormer Loft Conversion: What’s Included?
A standard 2VP dormer loft conversion covers:
- Pre-contract: measured survey, structural calculations, building regulations drawings, party wall notice service
- Structure: new steel frame (typically 2 × RSJ beams), dormer box framing in timber or SIPs, zinc or flat EPDM roof membrane
- Fabric: insulation to Part L, new windows and rooflights, fascia and soffit, lead flashings
- Internals: staircase (purpose-made or proprietary), flooring, plasterboard and skim, 1 bathroom (spec-dependent)
- Services: extend central heating, electrical first and second fix, MVHR or mechanical ventilation
- Finishes: painting throughout, eaves storage joinery if specified
What is not included in a standard contract: furniture, curtains and blinds, external scaffolding if the neighbouring property requires separate access, and any specialist planning consultant fees above standard applications.
Velux vs. Dormer vs. Mansard: Which Is Right?
Choose Velux if:
- Your loft already has sufficient headroom (minimum 2.2m ridge height above the floor)
- You want the lowest disruption and fastest programme
- The property is in a conservation area with restrictions on external alterations
Choose a dormer if:
- You want a full bedroom and en-suite (typically requires a dormer to achieve standing headroom across the room)
- The property is semi-detached or mid-terrace
- You are in a standard residential area (PD rights apply)
Choose a mansard if:
- You want the maximum usable floor area
- You are in a terrace where a hip-to-gable isn’t possible
- You are planning to use the space as a primary bedroom suite with dressing room
Planning Permission: What You Need to Know
Most rear dormer loft conversions in London can proceed under Permitted Development Rights — meaning no planning application, just a Certificate of Lawful Development (roughly £100–£200 in council fees).
You will need Full Planning Permission if:
- The property is in an Article 4 Direction area (strips PD rights from most alterations)
- The extension is to the front or side elevation visible from the street
- The property is listed (Grade I, II* or II) — requires Listed Building Consent
- You want a mansard conversion (always requires full planning)
2VP handles all planning submissions in-house. We have strong relationships with conservation officers across the London boroughs we serve and have navigated challenging planning scenarios dozens of times.
Return on Investment
A standard dormer conversion in Fulham (SW6) adding a double bedroom and en-suite bathroom:
- Build cost: £70,000–£90,000 (balanced spec)
- Typical value uplift: £120,000–£160,000 (based on comparable sold prices)
- Net uplift over cost: £30,000–£70,000
The return varies significantly by postcode and specification. Prime Central London (SW3, W11) tends to show the strongest uplift. Outer boroughs have lower absolute build costs but also lower value uplifts per square metre.
Party Wall Agreements
Any loft conversion on a terraced or semi-detached property will trigger the Party Wall etc. Act 1996. You are required to serve notice on each adjoining owner at least 2 months before work begins. If they consent, works can proceed. If they dissent, an Agreed Surveyor process kicks in (typically adding £1,500–£3,000 per neighbour and 6–8 weeks to the pre-start programme).
2VP manages party wall notice service as part of every contract.
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We also offer same-day site visits across our core areas. If your postcode is SW6, SW3, SW11, W11, W4, W6 or W2 — call us on 020 8050 8968 and we’ll be with you today.
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Keep reading
- Hammersmith Loft Conversions: What W6 Allows40 cubic metres on a terrace, 50 on anything else — the Class B limits, what Hammersmith's conservation areas remove, and what the Article 4 does not touch.
- Which Loft Conversion Type: Head Height Decides FirstMeasure 1.9 m before you choose a loft type. What the four types cost in roof, in planning and in the room below — and which your head height rules out.
- Your Builder Has Overrun. What Now?A 32-week programme that ran close to two years. What to do first when a London build has stalled: stop paying, check the record, measure what is covered up.
- When Repointing Has Failed, and What Goes BackCement pointing on a soft London brick sends the damage into the brick instead of the joint. How to read a failed joint, and the mix that goes back.