London · Dormer · L-shaped · Hip-to-gable · Mansard · Velux
Dormer, L-shaped, hip-to-gable, mansard and rooflight loft conversions for London homes. We handle planning checks, party wall notices and Building Regulations from first survey to final snag.
A London loft conversion typically costs £28,000–£45,000 for a Velux conversion, £45,000–£80,000 for a dormer or L-shaped dormer and £75,000–£110,000+ for a mansard. Most rear dormers on houses outside conservation areas are Permitted Development, while mansards almost always need planning permission. Allow 4–16 weeks on site depending on the type.
Last updated 3 October 2026
London lofts are not all the same, and the right conversion depends on your roof shape, headroom and budget. Compare the five main options below, then open the page for your type for planning rules, costs and what to expect.
Most London houses. The best balance of space and cost.
Victorian terraces with a rear outrigger.
Semis and end-of-terrace houses with a hipped side roof.
Maximum space. Central London terraces.
Roofs with good existing headroom (2.2 m+).
Build-cost ranges before VAT, fees and fittings. On-site time excludes the 3–4 months of design, Building Regulations and planning that normally come first.
| Loft type | Best for | Planning | Typical cost | On site |
|---|---|---|---|---|
| Rear dormer | Most London houses. The best balance of space and cost. | Usually Permitted Development | £45,000–£70,000 | 6–12 weeks |
| L-shaped dormer | Victorian terraces with a rear outrigger. | Often needs a volume check or planning application | £60,000–£80,000 | 10–14 weeks |
| Hip-to-gable | Semis and end-of-terrace houses with a hipped side roof. | Usually Permitted Development outside conservation areas | £55,000–£95,000 | 8–12 weeks |
| Mansard | Maximum space. Central London terraces. | Almost always full planning permission | £75,000–£110,000+ | 10–16 weeks |
| Velux (rooflight) | Roofs with good existing headroom (2.2 m+). | Usually Permitted Development | £28,000–£45,000 | 4–6 weeks |
Want a figure for your own house? Try our free Loft Conversion Cost Calculator.
Before spending on drawings, check four things. These decide whether a conversion is straightforward, expensive or not worth doing.
Not sure? Request a free site survey and we will measure the roof void and tell you which route suits it.
Most loft conversions on houses in London can be built without a planning application, but only if they stay inside the Permitted Development limits. The main conditions are:
Mansards, front-facing dormers, and any conversion in a conservation area or Article 4 area need a full planning application. You can still apply for a Certificate of Lawfulness to confirm in writing that your scheme is Permitted Development, which buyers' solicitors will ask for when you sell.
Whichever route applies, loft conversions always need Building Regulations approval, including fire safety under Part B (a protected stair or escape window, fire doors and interlinked alarms), structural calculations for the new floor and steelwork, and insulation to Part L. Read our guides to Permitted Development in London, loft fire safety and Article 4 Directions.
We measure the roof void, check headroom and structure, and confirm whether your address sits in a conservation area or Article 4 zone.
Drawings and structural calculations, then either a Certificate of Lawfulness, a planning application or straight to Building Regulations.
Party wall notices served at least two months before work starts. Building Control applications and inspections handled throughout.
Work runs under a written JCT contract with staged payments tied to milestones. We finish with a full snagging walkthrough.
Two lofts of the same size can be £20,000 apart. The usual drivers are the loft type, the floor area, whether you add a bathroom, the structure you are working with, access for materials, and the specification of windows, stairs and finishes. A new en-suite typically adds £8,000–£15,000. Scaffolding, structural steel and party wall fees sit on top of the base build. Our guide to getting comparable quotes explains how to check that each builder is pricing the same scope.
Planning outcomes vary by borough, so each of our local pages covers the conservation areas, house types and council approach for that area.
Leave your details and we will send you honest advice on what your house allows and what it should cost. No obligation, no pressure.
Ready to talk now? Get a free quote →
In 2026, a Velux (rooflight) conversion typically costs £28,000–£45,000, a rear dormer £45,000–£70,000, an L-shaped dormer £60,000–£80,000, a hip-to-gable £55,000–£95,000 and a mansard £75,000–£110,000 or more. These are build-cost ranges before VAT, professional fees and fittings. The final figure depends on size, specification, access and your borough.
Often not. Velux conversions, most rear dormers and many hip-to-gable conversions on houses fall under Permitted Development, provided the volume stays within 40 m³ (terraces) or 50 m³ (semi-detached and detached). Permitted Development does not apply to flats, listed buildings or conservation areas and can be removed by an Article 4 Direction. Mansards almost always need full planning permission.
On site, a Velux conversion takes about 4–6 weeks, a rear dormer 6–12 weeks, an L-shaped dormer 10–14 weeks and a mansard 10–16 weeks. Allow a further 3–4 months before work starts for drawings, structural calculations, Building Regulations, any planning route and party wall notices.
Roof shape and headroom decide it. Victorian terraces with a rear outrigger suit an L-shaped dormer. Semis and end-of-terrace houses with a hipped roof suit hip-to-gable plus a rear dormer. Roofs with plenty of headroom can take a cheaper Velux conversion. A mansard gives the most space but needs planning permission. A free site survey confirms what your roof allows.
Around 2.2 metres from the top of the floor joists to the underside of the ridge is the usual minimum for a Velux conversion. Below that you will normally need a dormer or mansard to create usable height, which raises the structural cost. Most Victorian and Edwardian terraces have enough roof volume for a dormer.
Almost always on terraced and semi-detached houses. New steel beams usually bear on the party wall, so notices must be served on adjoining owners at least two months before structural work starts. Hip-to-gable walls built at the boundary need a one-month notice. We manage the notices as part of the project.
Sometimes, but Permitted Development rights do not apply to flats, so you need full planning permission plus freeholder consent, and the lease must allow for or be varied to include the loft space. Roof ownership is the first thing to check. See our leasehold flat guide for the full process.
Cost figures are indicative 2026 London ranges for planning purposes, build cost only and excluding VAT, professional fees and fittings. They are not a quotation. Planning and Permitted Development rules depend on your specific address, so always confirm with your local council or a Certificate of Lawfulness.
Free survey, straight advice, no pressure. If a loft conversion is not right for your house, we will tell you.
Get a Free Quote