Loft Conversion Cost in London 2026: The Complete Guide

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.

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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.

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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 fixed-price 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.

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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.

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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

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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.

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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.

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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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Get a Fixed-Price Estimate

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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.