How much a loft conversion costs in London depends on the type of conversion, the size of the loft, the specification you choose and how easy the property is to work on. This guide breaks down realistic 2026 London prices by conversion type, explains what drives the cost, and shows what a good quote should include.
Indicative loft conversion costs in London (2026)
| Conversion type | Indicative build cost | Space added | On site |
|---|---|---|---|
| Velux / rooflight | £30,000 – £50,000 | Limited | 4–6 weeks |
| Rear dormer | £45,000 – £80,000 | 15–20m² | 6–10 weeks |
| Hip-to-gable with rear dormer | £55,000 – £90,000 | 18–25m² | 8–12 weeks |
| L-shaped dormer | £55,000 – £95,000 | 20–25m² | 10–12 weeks |
| Mansard | £65,000 – £120,000+ | 25–35m² | 12–14 weeks |
Indicative 2026 London build costs. They exclude architect and planning fees, structural engineering, party wall and building control fees, and VAT. A free quote will be specific to your property.
What drives the cost
- The type of conversion. A Velux conversion barely touches the structure; a mansard rebuilds the rear roof slope and costs the most.
- The size. Larger conversions cost more in total but usually less per square metre, because fixed costs are spread further.
- The specification. An en-suite, bespoke joinery, sash windows to match the house and high-end finishes all add to the figure.
- Access and logistics. Scaffolding, parking suspensions and tight-site working cost more in inner London.
- The planning route. A mansard or a conservation-area property needs a planning application, which adds design and council fees.
What a good quote should include
A turnkey loft conversion quote should cover: scaffolding, structural calculations, steels and installation, roofing and weatherproofing, the dormer, windows, insulation, plastering, a staircase, electrics (first and second fix), plumbing for a bathroom, and building control sign-off.
Items often excluded from headline prices, and worth budgeting for separately: architect and planning fees, structural engineering, party wall surveyor fees, bathroom sanitaryware and tiling, wardrobes, and any consumer unit upgrade.
How to compare quotes
Compare like for like. Two quotes can differ by tens of thousands of pounds simply because one excludes the bathroom, the staircase or the scaffolding. Ask each builder to itemise what is and is not included, confirm whether VAT is included, and check that building control and structural calculations are covered.
Ways to reduce the cost
- Choose the simplest conversion that gives you the space you need — a rear dormer is usually cheaper than a mansard.
- Keep the layout simple, avoiding moving bathrooms or services unnecessarily.
- Match standard window sizes rather than bespoke frames.
- Do the decoration yourself if you are able to.
Frequently asked questions
Is a loft conversion worth it in London?
Usually yes. It adds a bedroom or bathroom without reducing your garden, and can add up to 20% to the value of your home. Per square metre it is often cheaper than moving.
Why are London loft conversions more expensive?
Higher labour rates, period properties that need careful work, and tight-site access all push London prices above the national average.
Does the price include an en-suite?
Not always. En-suites are often priced separately. Ask your builder to confirm whether sanitaryware, tiling and the plumbing run are included.
Get a specific quote for your loft
Call +44 (0) 203 355 5313 or use our contact form. We will survey your loft and give you a clear, itemised, free quote. See also our loft conversion service.