Loft conversion cost in the UK (2026 guide)

A loft conversion costs more the more the roof has to change. Which?'s step-by-step guide puts the main types in order of cost: rooflight is the cheapest, a dormer costs less than hip to gable or mansard, and mansards tend to be the most expensive (Which?, how to plan a loft conversion, read 12 October 2026). Its cost guide, based on BCIS data from 2025, says a large dormer conversion will cost almost twice as much as a small one (Which?, loft conversion costs 2026, read 12 October 2026). Which? publishes its pound figures to members only, so this guide does not repeat them. It gives you the order, the drivers and the checks, so you can read any quote critically.

How much is a loft conversion?

There is no single price, because a loft conversion is a small construction project and the roof you start with decides most of the bill. Which? defines its "small" conversion as 4 x 5 metres with two windows and its "large" one as 12 x 7 metres with four windows. Its tables show rooflight and dormer costs for both, and say prices include VAT.

Which? also gives a typical split of a loft conversion budget: labour 35 to 40%, materials 25 to 30%, fixtures and fittings 10 to 15%, planning and permissions up to 5%, and a contingency of at least 10%, or 15 to 20% if structural work is involved. That last line is the one people skip. If a quote has no contingency, you are carrying the risk.

We do not publish a price range of our own, and we are not quoting what builders on this site charge. The directory is still being filled town by town, so treat any figure you see elsewhere as a starting point and get written quotes.

Cost by conversion type

The table uses only what Which? states in its guides, read on 12 October 2026. It shows order of cost and time on site, not pound figures.

Sources: Which?, how to plan a loft conversion and Which?, loft conversion costs 2026.

Velux or rooflight loft conversion cost

A rooflight conversion leaves the roof shape and pitch alone and adds roof windows, a floor and stairs. That is why it is the cheapest, and why it gives the least extra space. It only works if you already have enough headroom. Which? gives the minimum as 2.2 metres across at least 50% of the floor area (Which?, loft conversion regulations, 24 April 2026). Measure before you get excited.

Dormer loft conversion cost

A dormer pushes out from the roof slope to create headroom and floor space. Which? says it costs less than a mansard or hip to gable conversion. For many semis and terraces it is the usual middle path. Because size drives the price so strongly, ask whether a quote is for a small dormer or a full-width one.

Hip to gable loft conversion cost

A hip to gable conversion straightens the sloping side of a hipped roof into a vertical wall. Which? says it only suits detached, semi-detached or end-of-terrace houses and costs more than a dormer. It is often combined with a rear dormer to make one large room. In England this is within permitted development only if the total volume stays within the limits below.

Mansard loft conversion cost

A mansard runs along the whole roof and turns the slope almost vertical. Which? says mansards tend to be the most expensive type of conversion and can be particularly expensive. Because it changes the roof so much, check with your council whether permitted development applies before you design anything.

What moves the price

Which? names labour as the largest slice of the budget, so your local labour market will shift a quote more than any single material. Beyond that, these are the points worth asking about.

• Region. Labour is 35 to 40% of the cost, so a London quote and a Newcastle quote for the same job are unlikely to match. Get quotes from builders who work near you.
• The roof you have. Trussed roofs, old purlin roofs and low pitches each need different structural work. The roof type decides which conversion types are realistic.
• Structural steel. Which? says the structure must be assessed by a professional structural engineer to make sure it is safe. Ask who designs and signs off the steelwork, and whether the calculations are in the price.
• Stairs. For a habitable room Which? says the stair must be permanent, not foldaway. Fitting a full staircase can take space from the floor below, and some quotes leave it as an allowance.
• Fire safety. Building regulations Part B (fire safety) is covered by Approved Document B for dwellings, which GOV.UK lists as the 2019 edition with later amendments, updated September 2026 (GOV.UK, Approved Document B). Which? lists at least two escape routes including escape windows, fire-resistant doors and a smoke alarm. Expect a protected stair route and fire doors to appear as costed items.
• Party wall. If the work touches a wall you share, you must give notice. Surveyor costs can add to the budget.
• Extras. Scaffolding, an en-suite, new radiators, electrics and decoration are the usual line items that differ between quotes.

Do you need planning permission?

In England, a loft conversion on a house is often permitted development, which means no planning application, if it stays within set limits. The Planning Portal (read 12 October 2026) lists these conditions:

• The extra volume, including any earlier roof extension, must not exceed 40 cubic metres for a terraced house or 50 cubic metres for any other house.
• On the front of a house facing a highway, the extension must not go beyond the existing roof slope.
• The original eaves must be kept, and the extension should be set back at least 20cm from them where practicable.
• Materials must be similar in appearance to the existing house.
• No verandas, balconies or raised platforms. A Juliet balcony with no platform would normally be fine.
• Side-facing windows must be obscure-glazed, and any opening part must be at least 1.7 metres above the floor.
• The house must not be on designated land, such as a conservation area, National Park or World Heritage Site.

These rights apply to houses, not flats, and your council may have removed them with an Article 4 direction. Check with your local planning authority before you commit, or apply for a lawful development certificate if you want it in writing.

Wales has its own guidance with the same 40 and 50 cubic metre figures, and says UPVC is not acceptable apart from possibly windows (Welsh Government, loft conversions, page undated when read). Scotland is separate again. mygov.scot (updated 20 November 2025) says many roof additions do not need planning permission but you must check with your council.

Building regulations and building control fees

Building regulations approval is needed for a loft conversion however the planning side is settled. Which? says the work must comply "regardless of whether or not you need planning permission", covering structure, fire safety and sound insulation between the loft and the rooms below. Our guide to building regulations for home improvements explains the process. In Scotland you need a building warrant instead: mygov.scot (updated 24 November 2025) lists "converting a loft or garage into a room".

Fees are set by each council or approved inspector. Two published examples show the spread:

• Oxford City Council: from 1 April 2026, a loft conversion up to 100 square metres is £992 excluding VAT, or £1,190 including VAT, for full plans or a building notice. Larger ones are by quotation (Oxford City Council).
• Leeds City Council: full plans for a loft conversion with a dormer and one or two habitable rooms is £800 including VAT, and £900 for three or more. The same work without a dormer is £700 or £750 (Leeds City Council, no date shown when read).

Work done without approval costs more to put right. Both councils charge a higher regularisation fee, Leeds listing £900 to £1,150 and Oxford £1,488.

VAT on a loft conversion

Most building work to an existing home is charged at the standard rate. HMRC's VAT Notice 708 says work to an existing building is normally standard-rated, with a 5% reduced rate for some conversions, but only where the number of single-household dwellings changes (GOV.UK, Notice 708, updated 26 August 2026). Finishing a loft within your own house does not change the number of dwellings, so assume the standard rate and ask your builder to confirm in writing. Check whether each quote includes VAT, because Which?'s own tables do.

How long does a loft conversion take?

Which? puts rooflight conversions at around four weeks, dormers closer to five, hip to gable around seven and mansards closer to eight. Add time before the start for drawings, structural design, any party wall process and building control approval. Planning permission, when needed, adds its own wait.

Party wall notices

If your loft work affects a wall shared with a neighbour, the Party Wall etc. Act 1996 applies. GOV.UK's explanatory booklet says a party structure notice must be served at least two months before the planned start, and that a neighbour should reply in writing within 14 days. If there is no reply, a dispute is treated as having arisen and surveyors settle it. The building owner usually pays for the award where the works are for their benefit (GOV.UK booklet, published 12 May 2016). The booklet says it is not an authoritative interpretation of the law, so take advice on your own case.

How to compare loft conversion quotes

Three written quotes are the minimum, and the numbers only mean something if they price the same job. Give every builder the same drawings and ask each to show these separately:

1. Conversion type and floor area, with the roof changes described.
2. Structural engineer's design and steelwork.
3. Staircase, including the work on the floor below.
4. Fire safety items: doors, escape window, alarms.
5. Insulation, electrics, plumbing and plastering.
6. Scaffolding, skip, and building control and party wall fees, or a note that you pay them.
7. VAT, payment stages and a contingency.

A price well below the others usually means a different or thinner scope, so ask why. Our guide to hiring a builder in the UK covers insurance, contracts and staged payments.

Find a checked builder for your loft

MyLocalBuilders.uk lists builders by verified reviews from the last 12 months, then distance, and nobody pays to move up the ranked list. Your enquiry goes to one builder only. The directory is still being filled town by town, so check the results for your area. You can search for a loft conversion builder, read about loft conversions or browse by city. Whoever you pick, confirm insurance and any scheme membership on the scheme's own site first.