Last Updated on September 17, 2026
A rooflight (Velux) loft conversion typically costs £22,500 to £30,000. A dormer runs £40,000 to £60,000, hip-to-gable £50,000 to £70,000, and a mansard £50,000 to £80,000. London adds roughly 10 to 20 per cent, and quotes rarely include VAT, bathrooms, or decoration.
Checked on 11 September 2026.
Loft conversion prices by type
Figures below were published on Checkatrade’s cost guide, seen 11 September 2026, based on a 30 square metre conversion.
| Conversion type | Typical range | Rough per m2 | Build time |
|---|---|---|---|
| Rooflight (Velux) | £22,500 to £30,000 | £920 | 4 to 6 weeks |
| Dormer | £40,000 to £60,000 | £1,670 | 10 to 12 weeks |
| Hip-to-gable | £50,000 to £70,000 | £2,000 | 10 to 12 weeks |
| Mansard | £50,000 to £80,000 | £2,170 | 10 to 12 weeks |
Resi’s 2025 cost guide, seen the same day, puts the overall UK range higher at £55,000 to £120,000, with London builds at £60,000 to £130,000 against £50,000 to £80,000 outside London. The gap between the two guides is a useful lesson in itself: published averages vary a lot depending on spec and who is counting. Treat every figure on this page as indicative and get real quotes.
The London premium is real. Resi’s regional data shows a main dormer at £56,163 in London against £49,000 in the East Midlands, seen 11 September 2026.
What a quote usually includes, and what it usually does not
Most builder quotes for a loft conversion cover:
- Structural work, including steels where needed
- The staircase (simple flights run £1,200 to £2,500 on Resi’s figures; bespoke £6,000 to £9,000)
- Insulation to current standards
- First-fix plumbing and electrics
- Building control liaison
What is usually extra, and catches people out:
- VAT. Resi states its estimated costs exclude VAT. A VAT-registered builder adds 20 per cent. Ask which basis the quote uses before you compare it with anyone else’s.
- Bathroom fit-out. The pipework may be in the quote. The suite, tiling, and fitting often are not.
- Decoration and flooring. Plastering is usually included, paint and carpet usually are not.
- Professional fees. Structural engineer £500 to £1,000, building regulations package £700 to £1,200, party wall surveyor £500 to £1,500 (all Resi figures, seen 11 September 2026).
What moves the price
Head height. You need around 2,500mm of internal height at the ridge to convert comfortably, per HomeOwners Alliance guidance. Less than that and you are either lowering ceilings below or raising the roof, both expensive.
Where the stairs land. A staircase that stacks over the existing flight is cheap. One that eats into a bedroom means reconfiguring the floor below, and the cost climbs.
Steel requirements. Almost every conversion needs new steel beams to carry the floor. Awkward access, long spans, or a crane lift all add money.
Adding a bathroom. Moving soil pipes and upgrading the boiler or water pressure can add several thousand pounds beyond the fit-out itself.
Roof shape. A hipped roof (sloping on the sides) usually needs a hip-to-gable rebuild to create usable space, which is why it costs more than a straight dormer.
Building regs always apply, planning often does not
Many loft conversions fall under permitted development, so no planning application is needed. That is not the same as no rules. Every loft conversion must comply with building regulations: structure, fire escape, insulation, stairs. Checkatrade’s guide is blunt about it, and it is right. You need building control sign-off and a completion certificate at the end. Without that certificate you will struggle to sell the house.
If you share a wall with a neighbour, you will likely need a party wall agreement. HomeOwners Alliance notes this applies to most terraced and semi-detached homes and top-floor flats. Budget £500 to £1,500 per neighbour if a surveyor is needed.
The two-minute quote check
Before accepting any loft conversion quote:
- Find the staircase line. If the quote has no itemised staircase, ask why. A conversion without compliant stairs is a storage room, not a bedroom.
- Ask what the VAT position is. Is the figure inclusive, exclusive, or is the firm not VAT-registered? Get it in writing.
- Ask who handles building control. The builder should name the route: local authority or approved inspector. If they shrug, walk.
- Check the exclusions list. Bathroom fit-out, decoration, flooring, skip hire, scaffolding. If the quote does not say, assume they are extra.
- Get three quotes. HomeOwners Alliance recommends at least three. Wide gaps between them usually mean the specs are not comparable, so make them comparable before choosing.
For builders: what to publish on your own site
Most loft conversion firms publish nothing about price, which is why customers arrive anchored to a national average that may not fit your area. Publish:
- Real from-prices for each conversion type you offer, dated, with the spec they cover
- A plain list of what your quotes include and exclude, especially VAT, stairs, and bathroom fit-out
- Your building control route and who manages it
- Your public liability insurance and any TrustMark or FMB membership, with the number so it can be checked
- Two or three completed jobs with the final price band alongside the photos
A dated price page with honest exclusions wins the customers who have been burned by a lowball quote elsewhere. It also filters out the callers you would have lost at quote stage anyway.
Red flags in a loft conversion quote
- No mention of building control. Every conversion needs it. A builder who does not raise it is planning to skip it.
- No staircase line in the quote. The stairs are structural, regulated, and often £2,000 to £9,000. Silence here means a surprise later.
- A large deposit up front. Staged payments tied to completed work are normal. 30 to 50 per cent before a tool is lifted is not.
- A price far below every other quote with no spec difference. Something is missing, and you will pay for it in extras.
- “You don’t need building regs if you don’t get planning.” False. The two are separate. Regs always apply.
What this page does not cover
This page covers standard loft conversions on houses. It does not cover flat conversions needing freeholder consent, listed buildings, or conservation area constraints. It does not price bathroom suites, kitchens, or furniture. It is not a planning or legal guide; check gov.uk and your local authority for your own case. Extending outwards instead of upwards? See our separate guide to extension costs at /for/builders/extension-cost-uk/.
Method and limits
All figures were read live from the named source pages on 11 September 2026. Checkatrade’s ranges assume a 30 square metre conversion; Resi’s figures come from its own project data and skew higher. None of the figures is a quote. Prices vary by region, roof shape, and spec, and the two guides disagree on averages, which is normal for published cost data. Treat everything here as indicative and verify against real quotes.
Sources
- Checkatrade loft conversion cost guide. Cost ranges by conversion type, per square metre rates, build times, building regulations note. Seen 11 September 2026.
- HomeOwners Alliance: loft conversion, where do I start. Head height requirement (2,500mm), party wall guidance, three-quote advice. Seen 11 September 2026.
- Resi loft conversion costs guide. London and regional ranges, staircase and professional fee costs, standard quote exclusions including VAT. Seen 11 September 2026.
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