What will a loft conversion cost?
A loft conversion is one of the highest-return ways to add a bedroom without losing garden. But "loft conversion" covers everything from a simple rooflight to a full mansard, and the price swings hugely. Pick the type, what it's becoming, the finish and your region, and we give you an indicative UK price range with an en-suite, feature glazing and the fees broken out. A number to plan around before you call an architect. Free, no sign-up.
A guide, not a quote. The ranges are typical 2025/26 UK all-in prices — design, structural steels, the floor and roof works, the staircase, insulation, electrics, plastering, decoration and the trades, inclusive of VAT — drawn from published industry averages. They exclude a low or restricted head height needing the roof raised, removing a chimney, knock-on works to the floor below, and unusually high-end bathrooms or bespoke glazing. The only real number is a measured, written quote from a loft-conversion specialist or builder, and you should get at least three. Nothing you type leaves your browser.
The type sets the price; head height decides whether you can do it at all.
Start with head height. Before cost, check you've got the height — you generally want at least 2.2–2.4m from the existing ceiling joists to the ridge at the highest point. Too low and you're into raising the roof or lowering the ceiling below, which changes everything. A loft-conversion firm will measure it for free.
The four main types, cheapest to dearest. A rooflight (Velux) conversion just adds windows in the existing roof slope and boards it out — cheapest, but only works if you already have the headroom. A dormer builds a box out of the slope to add floor space and headroom — the most common choice and the value sweet spot. A hip-to-gable extends a sloping side wall up to a vertical gable, used on semis and detached homes for more width. A mansard rebuilds a whole side of the roof to near-vertical — the most space and the best look, but the most expensive and most likely to need planning.
The staircase eats space twice. Building regs require a proper fixed staircase (not a ladder) with headroom over it, and that stairway has to come up from the floor below — so you lose a little space on that floor too. A good designer hides it over the existing stairs; a bad layout wastes a bedroom's worth of landing.
Building regs and the Party Wall Act always apply. Even when the loft is permitted development, it must meet building regs — especially fire escape (often a protected stairway and fire doors all the way down) and insulation. On a terrace or semi you'll need a Party Wall agreement with the neighbours either side, which means a surveyor and a few weeks' notice. Budget the fees; don't skip them.
Get three quotes — and check the head height claim. Prices for the same loft vary widely between a national loft firm and a local builder. Get three written quotes on a like-for-like spec, confirm the staircase position and the fire-escape strategy, and make sure structural steels and building control are included. A budget worked out in advance is your strongest negotiating position.
Keep your loft project in one place.
Stead's home improvements log tracks the budget against what you actually spend, holds the building-control completion certificate and the structural calculations, and keeps the receipts and guarantees you'll want at sale time — all alongside the rest of your home's record.