Loft Conversion Cost UK 2026: The Complete Price Guide
What does a loft conversion actually cost in 2026? We break down the numbers by type, size, and region - with trade-by-trade detail so you know exactly where your money goes.
A loft conversion is one of the best-value ways to add space to your home without eating into your garden. But the price range is enormous - from £22,000 for a basic Velux to £80,000+ for a full mansard - and it's easy to get caught out if you don't know what drives the cost.
Here's what a loft conversion actually costs in 2026, what affects the price, and how to make sure your builder's quote covers everything.
Quick cost summary
For a standard 3-bed semi in England:
| Conversion type | Typical cost range | Avg floor area |
|---|---|---|
| Velux (rooflight) | £22,000–£35,000 | 15–25m² |
| Dormer (rear) | £35,000–£55,000 | 20–30m² |
| Hip-to-gable | £42,000–£60,000 | 25–35m² |
| Hip-to-gable + rear dormer | £50,000–£70,000 | 30–40m² |
| Mansard | £55,000–£80,000+ | 30–50m² |
These are all-in costs for the Midlands and North. Add 15–30% for London and the South East.
Costs based on BCIS regional benchmarks and MyBuildAlly quote analysis, Q1 2026. Your actual costs will vary based on specification, access, and local labour rates.
What type of loft conversion do you need?
Not every loft suits every conversion type. Your roof shape and what you want to use the space for will narrow down your options quickly.
Velux (rooflight only)
The cheapest option. No structural changes to the roof - just rooflights cut into the existing slope, plus a staircase, floor reinforcement, insulation, and a basic fit-out.
Best for: Home offices, spare bedrooms, playrooms where you don't need to stand at full height across the whole room.
Limitations: Usable floor space is limited by the roof pitch. If your ridge height is under 2.2m, this probably won't work.
Cost: £22,000–£35,000
Rear dormer
The most popular type in the UK. A flat-roof box structure extends out from the rear of your roof, giving you full standing height across most of the new room.
Best for: Master bedrooms with en-suite, family bathrooms, large home offices.
Why it's popular: You get the most usable space for the money. Most rear dormers fall under permitted development, so no planning application needed.
Cost: £35,000–£55,000
Hip-to-gable
If your house has a hipped roof (the side slopes inward rather than ending at a flat gable wall), this conversion extends the side wall up to create a full gable end. This gives you more internal floor area before you even add a dormer.
Best for: Semi-detached and detached houses with hipped roofs. Often combined with a rear dormer for maximum space.
Cost: £42,000–£60,000 (hip-to-gable only) or £50,000–£70,000 (with rear dormer)
Mansard
The most expensive but most spacious option. The entire roof structure is rebuilt with near-vertical walls and a flat top. Effectively adds a full new storey.
Best for: Terraced houses in London and the South East where land values justify the cost. Period properties where other conversions don't suit.
Planning note: Mansard conversions almost always need full planning permission - they change the shape of your roof from every angle.
Cost: £55,000–£80,000+
Where the money goes
Whatever type you choose, the cost splits roughly like this:
Structural work - 25–35%
Steel beams, floor reinforcement, roof alterations, and any wall modifications. This is the bit you can't see once it's done - and the bit you absolutely cannot cut corners on.
A structural engineer will design the steelwork (£400–£800 for calculations). The steel itself plus installation typically runs £2,000–£6,000 depending on spans.
Staircase - 8–12%
Getting up to your new loft is more expensive than most people expect. A standard staircase costs £2,500–£5,000 including the opening in the existing ceiling. Space-saving or spiral stairs are cheaper to buy but more expensive to install and less practical to live with.
The position of your staircase affects the layout of both the loft and the floor below - get this right early.
Insulation and fire protection - 8–10%
Building regulations require specific insulation values (0.18 W/m²K for a roof conversion) and 30-minute fire resistance on the new floor, staircase enclosure, and any doors opening onto the escape route.
This means:
- 100mm+ rigid insulation between and over the rafters
- Fire-rated plasterboard throughout the staircase enclosure
- Self-closing fire doors on every room opening onto the staircase (including existing bedrooms below)
- Mains-wired interlinked smoke and heat alarms on every level
Budget: £3,000–£6,000
First fix - 12–15%
Plumbing, electrics, and plastering. If you're adding a bathroom or en-suite to the loft, first-fix plumbing gets expensive because you're running waste pipes and water supply through the existing house - often across ceilings on the floor below.
| Item | Cost |
|---|---|
| First-fix electrics (lighting, sockets, extractor fan) | £1,200–£2,500 |
| First-fix plumbing (en-suite rough-in) | £1,500–£3,500 |
| Plastering (skim coat on plasterboard) | £1,500–£2,500 |
Second fix and fit-out - 20–30%
This is where your choices make the biggest difference to the final price:
| Item | Budget | Mid-range | Premium |
|---|---|---|---|
| En-suite bathroom (full supply & fit) | £3,000–£5,000 | £5,000–£9,000 | £10,000–£18,000 |
| Rooflights (per window, supply & fit) | £800–£1,200 | £1,200–£2,000 | £2,000–£3,500 |
| Flooring | £500–£1,000 | £1,000–£2,500 | £2,500–£5,000 |
| Built-in storage (eaves) | £1,000–£2,000 | £2,000–£4,000 | £4,000–£8,000 |
| Decoration | £500–£1,000 | £1,000–£2,000 | £2,000+ |
Scaffolding - 3–5%
Every loft conversion needs scaffolding, and it stays up for the duration. Typical hire for a 10–14 week project: £1,500–£3,500. Mansard conversions need more extensive scaffolding - budget £3,000–£5,000.
Regional price differences
Loft conversion costs vary significantly across the UK. Labour rates and material delivery costs are the main drivers.
| Region | Factor vs national avg | Velux range | Dormer range |
|---|---|---|---|
| Greater London | ×1.20–1.35 | £28,000–£45,000 | £45,000–£72,000 |
| South East | ×1.10–1.20 | £25,000–£40,000 | £40,000–£64,000 |
| South West | ×1.00–1.10 | £23,000–£37,000 | £36,000–£58,000 |
| Midlands | ×0.95–1.05 | £22,000–£35,000 | £34,000–£55,000 |
| North West | ×0.90–1.00 | £20,000–£33,000 | £32,000–£52,000 |
| North East | ×0.85–0.95 | £19,000–£31,000 | £30,000–£50,000 |
| Scotland | ×0.90–1.00 | £20,000–£33,000 | £32,000–£52,000 |
| Wales | ×0.85–0.95 | £19,000–£31,000 | £30,000–£50,000 |
Do you need planning permission?
Most loft conversions don't. Rear dormers and Velux conversions usually fall under permitted development - meaning no planning application needed, as long as you meet these conditions:
- The volume added doesn't exceed 40m³ (terraced) or 50m³ (detached/semi)
- The dormer doesn't extend beyond the existing roof plane at the front
- No part of the conversion is higher than the existing ridge
- Materials match the existing house
- Side-facing windows are obscure-glazed and non-opening (below 1.7m)
- You're not in a conservation area, AONB, or listed building
You will need planning permission for:
- Mansard conversions (they change the roofline from every angle)
- Front-facing dormers
- Properties in conservation areas or AONBs
- Any conversion that exceeds permitted development limits
Even if you don't need planning permission, you still need building regulations approval - and you might want a Lawful Development Certificate (£258) to prove everything was done properly when you come to sell. Read our planning permission guide for the full picture.
Hidden costs most people miss
These sit outside the builder's main quote but still hit your bank account:
| Item | Cost |
|---|---|
| Structural engineer calculations | £400–£800 |
| Building regulations application | £500–£1,000 |
| Party wall agreement (if applicable) | £700–£1,500 per neighbour |
| Mains-wired smoke/heat alarms (all levels) | £300–£600 |
| Loft ladder removal + ceiling make-good | £200–£400 |
| Temporary storage for loft contents | £100–£200/month |
| Redecoration of landing/stairwell below | £500–£1,500 |
| New radiators or UFH extension | £800–£2,000 |
| Boiler upgrade (if existing can't handle extra load) | £2,500–£4,500 |
For a full breakdown of the costs that don't appear on builder's quotes, read our hidden costs of home renovations guide.
How long does a loft conversion take?
| Type | Typical duration |
|---|---|
| Velux | 4–6 weeks |
| Rear dormer | 6–10 weeks |
| Hip-to-gable + dormer | 8–12 weeks |
| Mansard | 10–14 weeks |
Most of the work happens from inside the loft, so disruption to the rest of the house is relatively low compared to a ground-floor extension. The noisiest weeks are the first two (structural steel, roof opening) and the staircase installation.
Is a loft conversion worth it?
In most parts of the UK, a loft conversion adds more value than it costs - especially if you're adding a bedroom with en-suite to a 3-bed house.
| Type | Typical cost | Estimated value added | ROI |
|---|---|---|---|
| Velux (bedroom) | £28,000 | £20,000–£30,000 | 70–110% |
| Dormer (bedroom + en-suite) | £45,000 | £35,000–£55,000 | 75–120% |
| Hip-to-gable + dormer | £60,000 | £45,000–£70,000 | 75–115% |
| Mansard (full floor) | £75,000 | £55,000–£90,000 | 75–120% |
The return depends heavily on your area. In London and the South East, the value added almost always exceeds the cost. In lower-value areas, a top-spec conversion may not pay for itself - but you get the space to live in, which is worth something too. For regional cost detail, see our London extension cost guide and North of England extension and loft costs.
How to make sure your quote covers everything
Loft conversion quotes are some of the most variable we see. One builder quotes £38,000, another quotes £52,000 for what looks like the same job - but the scopes are completely different.
Check your quote includes:
- Structural steelwork (supply and install)
- Floor strengthening to the new loft floor
- Staircase (supply and install, including opening in existing ceiling)
- All building regulations requirements (fire doors, insulation, alarms)
- Scaffolding for the full duration
- Skip hire and waste removal
- Plastering, decoration, and final clean
- Whether the en-suite is supply-and-fit or fit-only
Common exclusions to watch for:
- Structural engineer fees
- Building regulations application
- Party wall agreements
- Flooring (often excluded even when everything else is included)
- Light fittings and switches
- Radiator extension from existing system
- Redecoration of existing landing and stairwell
Not sure if your quote covers everything? Upload it to MyBuildAlly and we'll flag scope gaps, check pricing against regional benchmarks, and tell you whether the numbers stack up. Our AI spots the things that are easy to miss when you're comparing quotes side by side.
Sources
- BCIS Average Building Prices - regional cost benchmarks, Q1 2026
- Spon's Architects' and Builders' Price Book 2026 - material and labour rate reference
- Approved Document B: Fire Safety - fire resistance and alarm requirements for loft conversions
- Planning Portal - permitted development limits and planning fees
- Analysis of residential construction quotes submitted to MyBuildAlly, January–March 2026