Loft Conversion Costs in the UK: A 2026 Budget Guide for Dormers, Roof Windows and Hip-to-Gable

Ask three builders what a loft conversion costs and you will get three different numbers, all of them defensible. That is not sharp practice. A loft is the most awkward space in a house to work in, and the price is shaped by your roof far more than by the floor area you end up with. A roomy loft under a steep Victorian pitch can be cheaper to convert than a cramped one under a shallow 1970s trussed roof, because the second one needs a dormer just to give you somewhere to stand up.

What follows are the sorts of ranges quoted across the UK for the main conversion types, along with the fees and structural costs that sit around them. Treat every figure as a starting point for your own quotes rather than a number to bank on, and expect regional variation of 20 to 40 per cent on the same specification.

What actually drives the price

Forget square metres for a moment. These are the things that move a quote most.

• Roof structure and pitch. Traditional cut-and-pitch roofs already have usable space inside them. Modern trussed roofs are engineered as a single unit and take considerably more work to open up.
• Head height at the ridge. Below roughly 2.1 to 2.2 metres of clear height in the middle, a straightforward rooflight conversion usually stops being viable.
• Whether you need a dormer. A dormer buys floor area, headroom and cost, roughly in that order.
• Access. Skips, steel and plasterboard all have to reach the loft. No side access, a shared entry or parking restrictions can add thousands.
• Who runs the job. A main contractor with a warranty costs more than hiring trades yourself — and carries far less risk.

Rooflight conversions: the simplest route

Often called a Velux conversion after the best-known brand, this is the least expensive way into a usable loft because the roof shape stays as it is. Expect somewhere in the region of £25,000 to £45,000 for a typical double room, depending on size, staircase position and where you live.

The money goes on floor joists, insulation, a compliant staircase, fire doors, wiring and a couple of roof windows. The trade-off is shape: you are working within the existing slopes, so much of the floor sits under low ceiling, and wardrobes rather than beds tend to end up against the kneewalls. If your ridge is low, this option may not be open to you at all.

Dormer conversions: more space, more money

A rear dormer raises the ceiling and pushes out a vertical wall, which transforms what you can fit in the room. Budget £40,000 to £65,000 for a typical rear dormer on a two- or three-bedroom house. A large box dormer, or a job that also moves a chimney or strengthens a sagging floor, can push past £70,000.

In England, a rear dormer is often permitted development, subject to volume limits of roughly 40 cubic metres for terraced houses and 50 for semis and detached homes. Rights can be removed by an Article 4 direction or a condition on a previous planning permission, so confirm the position with your local authority. A Lawful Development Certificate costs a few hundred pounds and is cheap insurance when you come to sell. Side dormers and front dormers almost always need planning permission.

Hip-to-gable and mansard conversions

A hip-to-gable conversion replaces the sloping side of a hipped roof with a full-height vertical wall, which is where the extra headroom and floor area come from. Typical figures run from £45,000 to £70,000, and higher if the new gable needs steel framing or the roof covering has to be renewed.

It is often paired with a rear dormer to create an L-shaped room, which is the most common way to get two bedrooms and a bathroom into a loft. Expect £55,000 to £80,000 for that combination.

A mansard rebuilds the roof with a steep, almost vertical face and is the most expensive common option, usually £60,000 to £90,000 or more. It almost always needs planning permission, and because nearly the whole roof is reconstructed, structural costs are correspondingly high.

Fees and reports you pay for before the builders arrive

These are easy to forget and they add up quickly.

• Planning application, if you need one: around £250 for a householder application in England, though fees are reviewed regularly, so check your council's current schedule.
• Lawful Development Certificate: a few hundred pounds where you want written confirmation that the work is permitted development.
• Building regulations application: commonly £400 to £900 for a domestic loft. A full plans application takes longer but avoids arguments on site.
• Structural engineer: £500 to £1,500 for beam and floor designs, depending on complexity.
• Party wall: around £700 to £1,500 plus the neighbour's surveyor's fee if the work affects a shared wall. Serving notice properly is far cheaper than a dispute.
• Asbestos survey: worth commissioning in any pre-2000 home before ceilings come down.

Scotland, Wales and Northern Ireland run their own systems, so check with your local authority rather than assuming English rules apply.

Structural work, staircases and finishes

The structure

Steel beams, new floor joists, trimming the roof and occasionally strengthening a gable can account for £10,000 to £25,000 of a dormer job on their own. Steel prices move, so ask how long the quote holds and whether it includes crane or hoist hire.

The staircase and the plumbing

A new staircase is often £2,000 to £6,000 fitted, and where it lands dictates much of the plan. Adding an en suite usually means running hot water up and waste down; if the fall is wrong, you will need a pumped waste system, which adds cost and a little maintenance.

The finishes

Insulation to current standards, plastering, doors, electrics with a Part P certificate, heating, flooring and decoration. A modest specification might come in at £8,000 to £15,000. Fitted wardrobes, a tiled en suite and bespoke joinery will comfortably exceed that.

Building a budget that survives contact with reality

1. Get three itemised quotes, not three lump sums. You cannot compare a job that excludes decoration with one that includes it.
2. Ask each builder to list what is not included: scaffolding, skips, decoration, bathroom fittings, making good.
3. Check insurance and accreditation — TrustMark, the Federation of Master Builders or a similar scheme — and ask for two recent local references you can visit.
4. Agree a payment schedule tied to stages. Only ever pay for work already done, and hold back a retention until snagging is finished.
5. Add a contingency of 10 to 15 per cent. Old houses hide things, and a chimney or a rotten purlin is not a builder's fault.
6. Put the programme in writing, including how long the roof will be open to the weather and who is responsible for the scaffold.

Before you sign anything, have the structure checked by a chartered structural engineer and confirm the planning position with your local authority. Advice at that stage is the cheapest part of the whole job. And if your conversion involves altering a shared wall, taking on debt, or a leasehold property, speak to a qualified surveyor, solicitor or financial adviser before you commit.

Photo: Didgeman / Pixabay