Loft conversion cost guide 2026

MyJobQuote puts the average loft conversion at £40,000 in 2026, with most projects taking 4 to 10 weeks, while the Federation of Master Builders (FMB) gives an overall range of £30,000 to £70,000. Each guide makes its own assumptions about floor area and finish, so we show every source in its own row rather than blending them. Read them as a guide to the gap between types rather than a price for your home.

No published guide gives prices for Sussex specifically. MyJobQuote gives £1,800 to £2,700 per m² for London and surrounding areas, and Which? says costs are higher in South East England, but neither offers a separate figure for Sussex towns. Treat the national figures as a starting point for planning your budget, and rely on local quotes for the real number.

None of MyJobQuote, Checkatrade or FMB says whether these figures include VAT, so ask every builder to state it clearly on the quote. MyJobQuote says labour is generally included in a typical quote, but decoration, flooring and fitted joinery are usually left out. FMB stresses that its figures are not quotes, and the MyJobQuote hip to gable guide gives different figures from MyJobQuote's main loft page, which is why both appear separately here.

The biggest single factor is how much the roof structure has to change. Moving from rooflights to a dormer, a hip to gable or a mansard adds steelwork, new roof framing and more scaffolding, and each step up adds both materials and weeks on site. MyJobQuote's labour figures show the pattern clearly: £9,000 to £14,000 for a Velux conversion, £20,000 to £40,000 for a dormer, £20,000 to £35,000 for a hip to gable and £25,000 to £45,000 for a mansard.

Floor area, the new staircase, whether you add a bathroom, the quality of windows and finishes, and how easy it is to get materials to the roof all push the price up or down. Which? gives an unlocked budget split of 35 to 40% for labour, 25 to 30% for materials, 10 to 15% for fixtures and up to 5% for planning, with contingency of no less than 10%, rising to 15 to 20% where there is structural work. Checkatrade says labour often accounts for around 30% and materials roughly 20%, which shows how differently sources divide the same budget.

Many loft conversions in England can be carried out under permitted development, which means you do not need to make a planning application, but only if the work meets every condition the Planning Portal sets out. The key limit is volume: the additional roof space, including any previous enlargements, must not exceed 40 cubic metres for a terraced house or 50 cubic metres for other houses. GOV.UK's householder technical guidance, last updated in 2019, gives the same limits.

Permitted development for lofts does not apply to flats or buildings containing flats, and roof extensions on Article 2(3) designated land, which includes conservation areas, are not permitted development. Where rights have been removed in your area, for example by an Article 4 Direction, you will need a householder application, which costs £548 in England from 1 April 2026 according to GOV.UK. Rules also differ for maisonettes and listed buildings, so check with your local planning authority before you commit to a design, and remember that no one can promise an application will be approved.

If you want certainty that your loft falls within permitted development, you can apply for a lawful development certificate for a proposed use. The Planning Portal says the fee is half the normal planning fee, a decision is due within 8 weeks, and having one is not compulsory. Applying before work starts gives you written confirmation of the position rather than leaving it as an assumption.

Published timescales vary by source as much as prices do, so expect a range rather than a fixed date. The figures below cover time on site only. Remember that planning, drawings, structural calculations and any party wall process happen before builders arrive, and these can take as long as the build itself.

To compare quotes fairly, give every builder the same drawings and specification, and ask for an itemised price that separates the structure, the staircase, any bathroom, and finishing work such as decoration and flooring. Check whether VAT is included, who is arranging building control and how that fee is covered, and what is excluded, such as party wall costs or skip hire. Ask how the work will be staged and paid for.

Getting more than one quote is the most reliable way to test published figures against your own roof. Through Sussex Builder you can request up to 3 free quotes from checked local builders, with no obligation, by using our loft conversion quote form or calling 01273 115520. If you are weighing up an extension instead, our guide to extension planning permission sets out the rules.