What does a loft conversion cost in London in 2026? Detailed cost breakdown

Loft conversion cost breakdown for London 2026

These figures represent realistic budget ranges for loft conversions in London as of early 2026, based on projects delivered across Greater London. All figures are for contractor-supplied labour and materials unless stated otherwise. Second-fix materials (sanitaryware, tiles, flooring, furniture) are client-supplied in the standard rcbGroup model.

Why London loft conversions cost more than national averages

London loft conversion costs are typically 25–40% higher than the UK national average, driven by:

• Higher labour rates (skilled tradespeople cost more in London than anywhere else in the UK)
• Higher material delivery costs (restricted-hours deliveries, ULEZ surcharges, limited site access in terraced properties)
• More complex fire safety requirements (London Building Control inspectors apply the full fire protection specification rigorously)
• Steeper party wall and structural requirements in London Victorian and Edwardian stock
• Higher skip and waste disposal costs (London tip charges and ULEZ costs for skips)

Velux (roof light) loft conversion — London 2026

A Velux conversion does not alter the roof structure — floor joists are strengthened, a staircase is installed, Velux windows are added, and the space is fitted out.

Element	Cost range
Structural floor upgrade (new joists, steel beam)	£4,000–£8,000
Staircase (softwood, standard layout)	£4,000–£8,000
Velux windows x2 (GGLSD MK06 or similar)	£1,500–£3,000
Insulation (roof slope, floor)	£2,500–£5,000
Fire protection (FD30S doors, stair enclosure, smoke alarms)	£3,000–£7,000
First-fix electrical (lighting, sockets, smoke alarms)	£1,500–£3,000
Plastering and boarding	£3,000–£6,000
Decorating (walls, ceiling, woodwork)	£2,000–£4,500
Snagging and contingency (10%)	£2,000–£4,500
Total range (room only, no bathroom)	£24,000–£49,000
Bathroom addition (first-fix plumbing, shower tray, basin, WC)	£8,000–£15,000
Total with en-suite	£32,000–£64,000

Note: architectural and structural engineer fees (typically £2,000–£5,000 for a Velux), Building Regulations fees (typically £1,000–£1,800), and VAT are additional.

Rear dormer loft conversion — London 2026

The most common loft conversion type in London. A full-width rear dormer on a Victorian terrace creates a substantial habitable room (25–35 sq m) with good head height.

Element	Cost range
Structural floor upgrade (new joists, ridge beam, steel)	£6,000–£12,000
Dormer structure (timber frame, flat roof, zinc or GRP finish)	£12,000–£22,000
Dormer window/glazing (1x full-width window or 2x casements)	£2,000–£5,000
Staircase (quarter-turn, softwood)	£4,000–£9,000
Insulation (roof slope, dormer walls, dormer flat roof)	£4,000–£8,000
Fire protection (FD30S doors all floors, stair enclosure, smoke alarms)	£4,000–£8,000
First-fix electrical	£2,000–£4,000
Plastering, boarding, finishing	£4,000–£8,000
External render/cladding to dormer face	£1,500–£3,500
Decorating	£2,500–£5,500
Contingency (10%)	£4,000–£8,500
Total range (room only, no bathroom)	£46,000–£93,500
Bathroom addition	£8,000–£18,000
Total with en-suite	£54,000–£111,500

Note: architectural and structural fees (typically £3,000–£7,000), Building Regulations fees (typically £1,200–£2,000), Party Wall Surveyor fees if applicable (£1,500–£3,000), VAT additional.

Hip-to-gable + rear dormer (L-shaped) — London 2026

This is the maximum-space option for a semi-detached or detached house with a hipped roof. Combined with a full rear dormer, it creates 35–50 sq m of usable loft space — typically two bedrooms plus bathroom.

Element	Cost range
Structural floor upgrade	£8,000–£15,000
Gable conversion (remove hip, build new gable wall, structural tie)	£10,000–£20,000
Full rear dormer structure	£12,000–£22,000
Windows and glazing	£3,000–£7,000
Staircase	£5,000–£10,000
Insulation throughout	£6,000–£12,000
Fire protection	£5,000–£10,000
M&E (electrics, first-fix plumbing)	£5,000–£10,000
Plastering and boarding	£6,000–£12,000
Decorating	£4,000–£8,000
Contingency (10%)	£6,400–£12,600
Total range (2 rooms, no bathroom)	£70,400–£138,600
Two-bathroom fit-out	£16,000–£35,000
Total with bathrooms	£86,000–£173,600

Mansard loft conversion — London 2026

Mansard conversions are the most expensive type due to the significant structural rebuilding of the rear roof slope. They are most common in central and inner London and where maximum floor area is required.

Element	Cost range
Structural floor and frame	£12,000–£22,000
Mansard rear wall and roof construction	£20,000–£40,000
Flat mansard roof (EPDM or zinc)	£5,000–£10,000
Full-height rear glazing/doors	£5,000–£15,000
Staircase	£5,000–£12,000
Insulation	£6,000–£12,000
Fire protection	£5,000–£10,000
M&E	£5,000–£12,000
Plastering and boarding	£6,000–£12,000
Decorating	£4,000–£8,000
Party wall and structural fees	£3,000–£6,000
Contingency (10%)	£7,600–£15,900
Total range (before fit-out)	£83,600–£174,900
Bathroom(s) fit-out	£10,000–£30,000
Total with bathrooms	£90,000–£200,000+

What's typically excluded from loft conversion prices

Standard loft conversion quotes from reputable London contractors will typically exclude:

• VAT (add 20% to all above figures)
• Architectural and structural engineering fees
• Building Regulations application fees
• Party Wall Surveyor fees
• Boiler relocation (if the boiler is in the loft)
• Water tank relocation (if a cold-water tank is in the loft)
• Second-fix materials (sanitaryware, tiles, flooring, kitchen furniture, light fittings)
• Carpets and soft furnishings
• Scaffolding costs if shared or specialist access is required

How to get an accurate loft conversion price in London

A genuine like-for-like quotation for a London loft conversion requires:

1. A site visit to assess the loft void, access, roof structure, party walls, and existing services
2. Architectural drawings (at minimum a measured floor plan and elevations)
3. Structural engineer's input on floor structure and any steelwork
4. Confirmation of the fire protection specification
5. Confirmation of the finish specification (materials, bathroom layout, etc.)

Any price given without a site visit and without drawings is a ballpark estimate only, and should be treated as such.