Loft Conversion Cost London (2026): Prices by Type

London loft conversion prices by type

These are typical London ranges. Use them to judge the scale of the project, then compare quotations for your actual design.

Loft type	About 30 m²	About 50 m²	Per m²	Build time
Rooflight (Velux)	£23,000–£34,500	£29,000–£46,000	£750–£1,150	4–6 weeks
Dormer	£40,500–£57,500	£52,000–£80,500	£1,350–£1,950	6–8 weeks
L-shaped dormer	£57,500–£69,000	£63,500–£80,500	£1,900–£2,300	Not stated
Hip-to-gable	£52,000–£69,000	£63,500–£80,500	£1,750–£2,300	6–8 weeks
Mansard	£70,000–£90,000	£85,000–£105,000	£2,300–£3,000 or more	8–10 weeks
Shell only	£23,000–£46,000	£34,500–£63,500	£750–£1,550	Not stated

Rear slope of a Victorian terraced house with three flush rooflights in a slate roof — Illustration: rooflight conversion. Typical London range for about 30 m²: £23,000–£34,500.

L-shaped rear dormer loft conversion clad in dark grey tiles on a Victorian terrace — Illustration: L-shaped rear dormer. Typical London range for about 30 m²: £57,500–£69,000.

Pair of 1930s semi-detached houses, one with a hip-to-gable loft conversion and one with its original hipped roof — Illustration: hip-to-gable on the left-hand semi. Typical London range for about 30 m²: £52,000–£69,000.

Rear mansard roof with a steep slate slope and two lead dormers on a Victorian terrace — Illustration: rear mansard. Typical London range for about 30 m²: £70,000–£90,000.

Prices checked 29 October 2026. Build times are for the construction stage only.

National figures for comparison

Typical starting prices are £30,000 for a rooflight conversion, £50,000 for a dormer, £60,000 for a hip-to-gable and £70,000 for a mansard. UK averages for 2026 are £27,500 for a Velux conversion, £50,000 for a dormer, £60,000 for a hip-to-gable and £65,000 for a mansard.

Costs that often sit outside the build price

Headline loft prices rarely cover every appointment and approval. Ask which of these each quotation includes, and budget separately for the rest.

Item	Typical cost	Basis
Architectural drawings	£440–£1,650	London
Structural engineer calculations	£650–£2,000	London
Householder planning application, England	£548 from 1 April 2026	England (3.8% rise on £528)
Building regulations approval	£850–£1,350	London
Party wall award, one agreed surveyor	£800–£1,000	London
Scaffolding hire	£1,800–£4,000	London
Staircase	£1,650–£2,750 standard; £5,500–£11,000 bespoke	London
En-suite bathroom	£3,000–£7,000	UK
Contingency	10% of the build cost	UK

Check the VAT basis of every figure. Most building labour and materials carry VAT at 20%, and quoted ranges do not always say whether they include it.

What pushes a London loft conversion price up

Two houses with similar roof areas can need very different work. These are the points that most often change the price.

Roof shape and structure

A hipped roof needs rebuilding as a gable before the room can be formed, and most conversions need new floor joists and specified steel or timber supports. Do not assume the existing ceiling joists can carry a habitable floor.

Mansards and terraced streets

A mansard rebuilds most of the roof, so it costs more than a dormer and its planning route must be checked for the property. On a terrace, work to shared walls usually brings party wall notices and surveyor costs.

Stairs, bathroom and services

The stair position decides how much of the floor below changes. An en-suite adds drainage, hot water and ventilation. Read our loft stair options guide and include plumbing and electrical work in the same brief.

Access, scaffolding and permissions

Narrow streets, no rear access and council licences for scaffolding or skips on the road add cost and time. Roof enlargements in conservation areas cannot use householder permitted development rights, so they need a planning application.

What is found when the work opens up

Textured ceilings and older materials may need a survey before they are disturbed. See our Artex and asbestos guidance, and keep the contingency for conditions that cannot be seen until work starts.

How long a loft conversion takes

The build itself typically runs from 4–6 weeks for a rooflight conversion to 8–10 weeks for a mansard. The time before the build is often longer.

Stage	What to allow for
Survey and design	Measured survey, drawings and structural calculations.
Permissions	Planning permission or a lawful development certificate, and building regulations approval.
Party wall notices	Notice must be given between 2 months and a year before work starts; neighbours have 14 days to reply.
Ordering	Steel, windows, rooflights and stairs can have lead times.
Build and handover	Structure and roof, weatherproofing, first fix, insulation and boarding, fitting, finishes and snagging.

Party wall notice periods: GOV.UK party walls guidance ↗, checked 29 October 2026. This is not legal advice.

Turn a price range into a quotation you can compare

A range tells you the scale of the project. A useful quotation shows what is in the price, so different builders’ figures can be compared like for like.

Part of the price	What it should show
Structure and roof	Floor joists, steels or supports, dormer or roof alterations, roof finishes and temporary weather protection.
Stairs and floor below	The new stair, openings, doors and making good to the rooms underneath.
Services	Electrics, heating, and drainage and hot water for any bathroom.
Insulation and finishes	Insulation, boarding, plastering, joinery, decoration and flooring, or a clear line where a shell package stops.
Exclusions and tax	Fees, approvals, provisional sums, client-supplied items and the VAT basis.

Vayton prices loft conversions from your drawings and structural information and sets out the agreed scope, exclusions and payment stages in writing. Compare what a shell loft conversion leaves out, and use our quotation checklist when the figures arrive.

Loft conversion cost questions

How much does a dormer loft conversion cost in London?

The London guide above gives £40,500–£57,500 for about 30 m² and £52,000–£80,500 for about 50 m², before separate fees. An L-shaped dormer is higher, at £57,500–£69,000 for about 30 m².

Read the dormer loft conversion guide

Is a mansard much more expensive than a dormer?

In the typical London ranges, yes: £70,000–£90,000 against £40,500–£57,500 for about 30 m². A mansard reshapes most of the roof and usually brings more structural, planning and party wall work, though it can give a fuller room.

Is a shell loft conversion cheaper?

The build price is lower because the work stops before the finishes, but you still pay to complete the room. Agree exactly where the shell package ends before comparing it with a finished conversion.

Can you price my loft from photographs?

Photographs help the first conversation. A price you can rely on needs measurements, drawings, structural information and the proposed stair route.

Plan the rest of the loft

Loft conversions in London · Loft conversion stairs · Shell loft conversions · Structural alterations

Loft conversion cost in London

Price the loft you want.