A loft conversion is often the best value space you can add: a whole new floor without extending the footprint. Here are the types, the costs, and the rules that decide what is possible.
Not every loft converts easily. A few things decide how straightforward, and how expensive, the job will be.
A specialist or structural engineer will assess it quickly and tell you which type suits your roof.
Loft conversions come in four broad forms, from the simplest rooflight scheme to a full mansard. Costs are indicative UK figures for 2026.
| Type | What it is, and typical cost |
|---|---|
| Rooflight / Velux | The cheapest: no change to the roof shape, just windows set into the existing slope. Around £25,000 to £40,000. Ideal where head height is already good. |
| Dormer | A box structure projecting from the roof to add head height and floor space. The most common choice. Around £30,000 to £65,000. |
| Hip-to-gable | Extends a sloping (hipped) side up to a vertical gable, creating far more usable volume. Around £33,000 to £70,000. |
| Mansard | Rebuilds the roof to a near-vertical rear (and sometimes front), giving the most space of all. Around £38,000 to £90,000-plus. Almost always needs planning permission. |
Many loft conversions can be done without a planning application, but the exceptions matter.
A standard loft conversion is often permitted development, meaning no planning application is needed, provided it stays within the volume limits (around 40 cubic metres for a terraced house, 50 for a detached or semi), does not raise the ridge, and does not sit forward of the roof plane facing a road. Permitted development does not apply if the home is listed, or in a conservation area or other designated area, where dormers visible from the road are usually refused and rooflight conversions are the safe route. Mansards almost always need planning permission.
Planning is about appearance; building regs are about safety, and every habitable loft needs them.
Whether or not you need planning, a habitable loft conversion always needs building control sign-off. That covers the structure (new floor joists, ridge and dormer beams, designed by a structural engineer), fire safety (a protected escape route, usually a fire door to a protected stair, and often mains-linked alarms), insulation, and the staircase. Budget for the structural calculations and the building control fees as part of the job.
The success of a loft is decided by a few practical details more than by the headline design.
Lofts are quicker and less disruptive than most extensions, and add strong value.
As a rough guide, a rooflight conversion takes around 4 to 6 weeks on site, a dormer 6 to 10 weeks, and a hip-to-gable or mansard, with more structural work, 10 to 16 weeks. Because a loft usually adds a bedroom and often a bathroom without touching the garden or footprint, it is one of the most reliable ways to add both space and value.
Head height and the staircase make or break a loft conversion. Establish that you have enough of the first, and where the second will go, before anything else. Every other decision follows from those two.
We handle loft conversions end to end: assessing whether the roof suits a rooflight, dormer, hip-to-gable or mansard, coordinating the structural design and building control, and building it cleanly with the rest of the house protected. We will give you a straight view on planning, cost and what the finished space will actually be like to use.
General guidance for 2026, written for homeowners in Surrey and Hampshire. It is a summary, not professional advice; confirm the details for your specific project.
Tell us about your roof and what you want from the space, and we will talk through the right type, the rules and a realistic cost.