Updated 26 October 2026 · SK Home Improvements
A loft conversion turns unused roof space into a habitable room such as a bedroom, office or bathroom. The four main types are roof-light, dormer, hip-to-gable and mansard, and most cost £30,000–£65,000 including VAT, depending on the type, the size and how much of the roof structure has to change.
What is a loft conversion and is your loft suitable?
A loft conversion turns the roof space above your top floor into a habitable room, such as a bedroom, office or bathroom, with a proper staircase, floor, insulation and windows. Most houses can be converted, but three things decide how easily: head height, roof structure and where the new stairs can go.
- Head height: a common rule of thumb is at least 2.2 m from the top of the ceiling joists to the underside of the ridge. Less than that often means a dormer, a mansard or lowering the ceilings below.
- Roof structure: older houses with traditional cut rafters are usually simpler to open up. Houses built with trussed rafters, common from the 1960s onwards, need more structural work, usually including steel beams.
- Stairs: the new staircase has to fit over the existing one without blocking the landing or taking too much space from a bedroom.
What are the main types of loft conversion?
There are four main types of loft conversion, and the shape of your roof usually decides which ones are possible.
- Roof-light conversion: the roof shape stays the same and windows are fitted into the existing slopes. It suits lofts that already have good head height and is usually the least disruptive.
- Dormer conversion: a box-shaped extension projects from the rear slope, giving full head height across much of the room. A rear dormer is the usual choice for terraced and semi-detached houses.
- Hip-to-gable conversion: on a house with a sloping (hipped) side roof, the side is built up into a vertical gable wall, creating more volume. It is often combined with a rear dormer.
- Mansard conversion: the rear roof slope is rebuilt almost vertical with a flat top, giving the most space. It is common on city terraces and usually needs planning permission.
How much does a loft conversion cost?
Most loft conversions cost £30,000–£65,000 including VAT. A simple roof-light conversion sits at the lower end, dormers in the middle, and hip-to-gable and mansard conversions towards the top, because they change more of the roof structure.
| Type | Structural change | Where it usually sits in the range |
|---|---|---|
| Roof-light | Minimal; roof shape unchanged | Lower end |
| Rear dormer | New dormer structure on the rear slope | Middle |
| Hip-to-gable with dormer | Side roof rebuilt as a gable wall | Middle to upper |
| Mansard | Rear slope rebuilt almost vertical | Upper end |
Adding an en-suite raises the price because of the extra plumbing, drainage, tiling and fittings. You can get a range for your house from our guide-price tool.
What else affects the price of a loft conversion?
Beyond the type, the price depends on size and on how much needs to change below the loft as well as in it. Common cost drivers include:
- The width of the dormer and the number of windows or roof lights.
- Steel beams, especially where trussed rafters have to be replaced.
- Moving water tanks, which often means a new hot water system or combi boiler.
- The staircase design and any changes to the landing or bedroom below.
- Fire safety work to the existing stairs and doors.
- Scaffolding, especially on a busy road or a tall house.
- Party wall costs if steel beams bear on a shared wall.
Moving the boiler or tanks and upgrading doors downstairs are often forgotten in early budgets, so make sure they appear in any quote you compare.
Do you need planning permission for a loft conversion?
Many loft conversions do not need a planning application because they fall under permitted development, but mansards, front dormers and roof changes on listed buildings, flats or homes in conservation areas usually do. In England, permitted development allows up to 40 cubic metres of extra roof space on a terraced house and 50 cubic metres on a detached or semi-detached house, provided the extension does not go beyond the roof slope facing a road, is no higher than the existing roof and uses similar materials. Side-facing windows must be obscure-glazed and fixed shut below 1.7 m above the floor, and balconies are not allowed.
Wales, Scotland and Northern Ireland each have their own rules for roof alterations. Our planning permission guide covers each nation, and we check your property before quoting.
What Building Regulations apply to a loft conversion?
Every loft conversion needs Building Regulations approval, or a building warrant in Scotland, because it creates a new habitable floor. Building control checks several areas:
- Structure: new floor joists strong enough for a room, and beams designed by a structural engineer.
- Fire safety: in a typical two-storey house, the stairway usually has to become a protected escape route, with fire doors to habitable rooms and mains-powered, interlinked smoke alarms.
- Stairs: a safe pitch, headroom and handrails. In England, the guidance allows slightly reduced headroom over loft stairs where space is tight.
- Insulation and ventilation: the roof, dormer walls and floor must meet current energy standards, with ventilation to avoid condensation.
- Sound: the new floor needs sound insulation between the loft room and the rooms below.
If beams are built into a shared wall in England or Wales, you will usually need to serve notice under the Party Wall Act.
How long does a loft conversion take?
A roof-light conversion typically takes 4 to 6 weeks on site, a dormer 6 to 10 weeks and a mansard or hip-to-gable conversion 8 to 12 weeks. Much of the early work is done from scaffolding, so you can usually stay at home.
The most disruptive stage is when the new staircase is cut in and the loft is opened up to the landing, which usually happens around two-thirds of the way through. Dust sheets and temporary screens help, but expect some mess on the top floor for a week or two. Before work starts, allow time for drawings, any planning application, building control approval and party wall notices.
What should you check before you commit to a loft conversion?
Before you commit, make sure the space you will get matches what you need. Useful questions to ask:
- How much floor area will have full head height, not just total floor area?
- Where will the stairs go, and what will you lose on the floor below?
- Where will the water tanks or boiler move to?
- Does the quote include fire doors, smoke alarms, an en-suite and decoration?
- Which approvals are needed, and who arranges them?
We survey your loft, measure head heights and explain which type of conversion fits before giving a written quote. See our loft conversions page and compare guide figures on the prices page.
Related services
- Loft conversions: guide £30,000–£65,000 inc VAT
Figures in this guide are typical UK ranges including VAT where it applies. They are not quotes. Rules on planning and building control differ between England, Wales, Scotland and Northern Ireland and change over time, so we check what applies to your property before quoting.