How much does a loft conversion cost in the UK? (2026)
Verified UK loft conversion costs in 2026 by type (Velux, dormer, hip-to-gable, mansard) plus what is actually included, planning routes, and the time-to-completion you should expect.
A UK loft conversion in 2026 costs between £15,000 for a simple Velux conversion and £75,000+ for a mansard. The most common format, a rear dormer, lands at £30,000–£60,000 in 2026 and is confirmed across Checkatrade, MyJobQuote, and Homebuilding & Renovating. London adds 25–40% on top of these national figures.
Quick answer
UK loft conversion costs in 2026: Velux/rooflight £15,000–£30,000; Dormer £30,000–£60,000; Hip-to-gable £45,000–£70,000; Mansard £45,000–£75,000. Average across all types is around £50,000, with a typical £/m² of £1,200–£1,800. London uplift: 25–40% above these national figures. On-site time: 4 weeks (Velux) to 16 weeks (mansard).
How to read this guide#
Two kinds of figures appear below:
- Headline price ranges (cost by conversion type, per-m² rates, total range): cross-referenced against multiple UK cost-guide publishers.
- Practical guidance (what is included, planning routes, structural considerations, scope gaps, and red flags): drawn from standard UK construction industry practice.
Headline ranges (verified)#
Cost by conversion type#
| Conversion type | Range | Typical £/m² |
|---|---|---|
| Velux / rooflight | £15,000 – £30,000 | £500 – £700 |
| Dormer (rear) | £30,000 – £60,000 | £1,150 – £1,700 |
| Hip-to-gable | £45,000 – £70,000 | £1,400 – £2,000 |
| Mansard | £45,000 – £75,000 | £1,400 – £2,000 |
UK average across formats: around £50,000. Total range across all types: £27,500–£75,000 (Checkatrade, HomeOwners Alliance).
These figures cover a fully-fitted conversion to second-fix: structural strengthening, insulation, plasterboarding, plastering, electrics, heating extension, lighting, flooring, and a staircase up. They exclude professional fees (architect, structural engineer, party wall surveyor), Building Control fees, and any en-suite bathroom unless specifically stated.
London uplift#
A standard dormer that costs £30,000–£60,000 nationally typically costs £40,000–£90,000 in London, with central London projects often exceeding £100,000. The uplift reflects higher labour rates, constrained access (most London terraces front directly onto the street), and stricter planning and conservation overlays.
Practical guidance (industry standard)#
What a loft conversion quote should cover#
A complete loft conversion build quote should typically include:
- Site setup, scaffold, and protection of existing floors and stair
- Structural strengthening (steels, joist upgrade, ridge beam if needed)
- Insulation to current Building Regulations (rafter and ceiling)
- New flooring deck on top of strengthened joists
- New stair from existing landing into the loft
- Roof works (rooflights or new dormer construction)
- Lead flashings, weatherproofing, and external dressing
- First-fix electrics: lighting circuits, sockets, smoke alarms
- Plasterboarding and plastering of all internal surfaces
- Second-fix electrics: switches, lighting fittings, sockets
- Heating extension from existing system
- En-suite bathroom (if specified) including waste connection
- Building Control sign-off
It often does not cover:
- Architect fees (£1,000–£3,000 typical)
- Structural engineer fees (£550–£1,900)
- Party wall surveyor fees (£900–£2,500 per neighbour where applicable)
- Building Control fees (~£850 plus VAT)
- Asbestos survey (~£250) and licensed removal if needed
- Bat survey (~£350) if the property is in a habitat zone
- Decoration after second-fix
- Carpets, blinds, fitted wardrobes
- Smart-home wiring beyond standard switching
- Connecting to existing TV, satellite, and data networks
When you compare loft conversion quotes, the easy mistake is comparing a £52,000 quote inclusive of professional fees and en-suite against a £45,000 quote that excludes both. Read the exclusions list line by line.
Planning permission and Permitted Development#
Most loft conversions in England fall under Permitted Development Rights and do not need full planning permission, provided they meet the volume and position limits:
- Terraced houses: up to 40 m³ added volume
- Semi-detached and detached: up to 50 m³
- No dormer extending forward of the principal elevation (front dormers always need planning)
- Side-facing windows obscure-glazed and non-opening below 1.7 m
- Materials similar to the existing dwelling
If your project is permitted development, applying for a Lawful Development Certificate (£100–£250) is recommended. It gives written council confirmation that the work is permitted and matters at sale time when the buyer's solicitor checks.
If your project needs full planning permission (mansard, side-facing dormer, listed building, conservation area), the householder application fee is £258 in England, and decisions take 8 weeks upward.
Structural considerations#
Every loft conversion involves structural work. The key elements:
- Steel beams to support the new floor and any opened-up space below. Typically 2–4 steels per dormer conversion. The structural engineer designs and specifies these against existing wall and floor loadings.
- Joist upgrade: existing ceiling joists are usually too small to serve as floor joists. Either deeper joists are added alongside, or the ceiling is sheared and re-spanned with engineered joists.
- Ridge beam or trusses: if the roof is a cut roof (rafters and ceiling joists), the structural engineer will specify how to keep the roof stable when the floor below is removed. If it is a trussed roof, the trusses must usually be cut and replaced with steel framing, one of the bigger cost items.
- Foundations: rare to need foundation work for a loft conversion, but heavy mansard projects on older properties sometimes do.
If the structural engineer recommends scope your builder did not quote for (additional steels, foundation underpinning), the cost will move materially. Get the engineer involved before signing the build quote.
Choosing between the conversion types#
The right format depends on three factors: existing head height, roof shape, and budget.
Velux / rooflight: only works when the existing ridge gives at least 2.4 m of usable head height under the rafters. No external shape change, fastest install, lowest cost, but the smallest gain in usable floor area. Best for a single bedroom.
Dormer (rear): adds vertical wall and head height to the rear slope. Doubles or triples the floor area available compared to a rooflight conversion. Most common UK format. Suits terraces and semi-detached homes.
Hip-to-gable + dormer: replaces a hipped end with a vertical gable wall, giving substantial extra space. Suits semi-detached and detached homes with hipped roofs. Combined with a rear dormer is the most common large-scale format.
Mansard: replaces the roof slope with near-vertical walls. Almost always needs planning permission. Common in London terraces. Most expensive due to the scale of structural and roofing work, but maximises usable floor area.
L-shaped dormer: a dormer on the rear plus a smaller dormer in the side return where one exists. Specific to late-Victorian/Edwardian terraces. Cost sits between dormer and mansard.
Time to completion#
| Conversion type | On-site time |
|---|---|
| Velux / rooflight | 4–6 weeks |
| Dormer | 6–10 weeks |
| Hip-to-gable + dormer | 10–14 weeks |
| Mansard | 12–16 weeks |
Allow another 4–8 weeks of pre-construction time for design, planning (if needed), structural calculations, party wall notices, and contractor scheduling. So total project elapsed time is roughly:
- Velux: 8–14 weeks
- Dormer: 10–18 weeks
- Mansard: 16–24 weeks
Red flags in loft conversion quotes specifically#
Beyond standard quote red flags (covered separately), some are loft-specific:
No structural engineer drawings referenced. A loft conversion without engineer-specified steels and joists is unsafe and will fail Building Control. A quote that does not reference SE drawings is either missing the scope or planning to skip it.
Optimistic timelines. A 6-week dormer is unrealistic. The minimum on-site time including weatherproofing is 8 weeks even on a straightforward project. Quotes promising 4 weeks for a dormer are either not factoring snagging and Building Control, or planning to hand over before the work is finished.
No mention of insulation U-values. Building Regulations require specific U-values for new roof and ceiling insulation (currently 0.18 W/m²K for pitched roofs). A quote that does not specify insulation type and depth is likely planning the cheapest spec, which may fail inspection.
No party wall provision. If your loft conversion involves any work to a wall shared with a neighbour (most terraces and semis), the Party Wall Act applies. A quote that does not mention party wall notices is missing a cost item that the homeowner will end up paying later.
No provision for staircase. A new staircase is needed in nearly every loft conversion. Some quotes leave this out as "your existing landing has space" without confirming the building regulations requirement for headroom over the stair (2 m clear). Confirm the staircase is included and meets regs.
Vague "make good" language. Lifting plasterboard ceilings on the floor below to install the new joists damages the existing finish. A proper quote includes the cost of making good below the loft level (plaster, paint, possibly a small amount of redecoration). "Make good where required" without a clear scope is usually too thin.
Comparing your loft conversion quote#
The quote checker on this site analyses each line item against current UK rates, flags missing scope (party wall, structural engineer, Building Control, insulation), and runs a Companies House check on the contractor. For a £45,000 conversion, the £14 cost is below the threshold of any sensible deliberation; the information returned closes the gap between "this looks roughly right" and "every line is accounted for".
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Frequently asked questions
- What is the cheapest type of loft conversion?
- A Velux (rooflight) conversion at £15,000–£30,000 in 2026, confirmed across MyJobQuote and Homebuilding & Renovating. It works only when the existing loft already has adequate head height (typically 2.4 m to ridge) and the roof structure does not need altering. It adds rooflights, insulation, flooring, plasterboard, electrics, and stairs without changing the roof shape externally.
- How much does a dormer loft conversion cost in 2026?
- Between £30,000 and £60,000 in the UK in 2026, confirmed across Checkatrade, MyJobQuote, and Homebuilding & Renovating. A small 20 m² dormer starts at around £30,000; a larger 30–40 m² dormer with an en-suite bathroom can reach £55,000–£75,000. London adds 25–40%.
- Do I need planning permission for a loft conversion?
- Often no. Many loft conversions in England fall under Permitted Development Rights, which allow rear dormers and rooflight conversions within volume and height limits (40 m³ for terraces, 50 m³ for semis and detached). Mansard conversions, side-facing dormers, and any work on listed buildings or in conservation areas usually need full planning. A Lawful Development Certificate (£100–£250) is recommended to confirm the work is permitted and is useful at sale time.
- How long does a loft conversion take?
- A simple Velux/rooflight conversion takes 4–6 weeks. A dormer takes 6–10 weeks. A hip-to-gable plus rear dormer takes 10–14 weeks. A mansard conversion takes 12–16 weeks. These are on-site durations; allow another 4–8 weeks of pre-construction time for design, planning, structural calculations, and contractor scheduling.
- Will a loft conversion add value to my home?
- Generally yes, particularly when it adds a usable bedroom with an en-suite. UK property data over the past decade suggests a typical loft conversion adds 15–20% to a home's value, more in high-demand areas. The economics work best when the cost is significantly less than the value added; for a £350,000 home in a strong market, a £40,000 loft conversion can add £55,000–£70,000 in value. Lower-value markets and lower-spec conversions narrow the gap.
- What's typically not included in a loft conversion quote?
- Common scope gaps: external scaffolding hire beyond the initial period, building control fees, structural engineer fees if engaged separately, party wall surveyor fees if neighbours appoint, plumbing connection to existing systems beyond the loft, decoration after second-fix, blinds and window dressings, fitted furniture, lift-and-relay of existing tiles or slates if the roof needs partial restoration, and asbestos removal if the existing roof contains it. Always read the exclusions list before signing.
Last updated: 7 May 2026