Loft Conversion Cost in 2026: What You'll Actually Pay, Room by Room

The gap between the cheapest and most expensive loft conversion is enormous, and it isn't random. Get a grip on what drives the number and you can budget with real confidence rather than guessing. This is a plain breakdown of the loft conversion cost you should expect in 2026, type by type, and where every pound tends to go.

The type of loft decides most of the cost

Before anything else, understand this: the type of conversion is the single biggest lever on price, often acting as a two to three times multiplier between the cheapest and dearest options on the same house. Everything else, finish, en-suite, region, moves the number within a band that your roof type has already set.

So the honest starting point isn't "how much does a loft conversion cost", it's "which type does my roof allow". Once you know that, the budget falls into a fairly predictable range.

Velux, the cheapest route

A Velux or rooflight conversion is the least expensive at roughly £22,000 to £40,000 in 2026. It adds windows into the existing roof slope without changing the roof shape at all, so you're paying for insulation, flooring, a staircase, plastering and the rooflights, not for rebuilding the roof.

The catch is head height. You need around 2.2 to 2.4 metres at the ridge for the finished room to work. If you have that, this is the fastest and cheapest way to gain a bedroom or office, and it usually stays within permitted development because nothing on the outside changes.

The dormer, the popular middle

The rear dormer is the UK's most popular type, and in 2026 it typically costs £30,000 to £65,000, with a mid-spec 24 to 28 square metre conversion sitting around £55,000 fitted. It projects a box out from the rear roof slope, giving proper head height and floor space where a Velux couldn't.

It suits most terraces and semis, and outside conservation areas a standard rear dormer often falls within permitted development. It's the sweet spot for a reason: full head height at a mid-table price. Strip out an en-suite and you save roughly £5,000 to £12,000.

Hip-to-gable and mansard, the bigger jobs

If your semi or detached house has a hipped roof, the hip-to-gable conversion straightens that sloping side into a vertical gable, unlocking far more volume. Expect roughly £33,000 to £90,000 in 2026, usually combined with a rear dormer, and note it nearly always needs planning permission because the roof shape changes.

The mansard is the priciest at around £38,000 to £95,000, with inner-London mansards at the very top. It rebuilds the roof to a steep near-vertical pitch, delivering the most floor area of any type, which is why it's the classic choice for Victorian terraces where nothing else gains enough space. It almost always needs full planning permission, and in conservation areas it's often the only loft form that will be approved. A well-planned dormer loft conversion is frequently the better-value middle ground when your roof gives you the choice.

Where the money actually goes

Break any loft conversion down and the costs sit in a few predictable places. The structural work, steel beams and floor reinforcement, is unavoidable because the original roof timbers were never built to carry a room. The staircase runs £2,000 to £4,000. Insulation, plastering and electrics add £8,000 to £15,000. Decoration is £1,500 to £3,000.

Two items catch people out. Scaffolding runs £2,500 to £6,000, and if a builder won't itemise it separately, that's a warning sign. And an en-suite bathroom adds £6,000 to £15,000 on top, so decide early whether you want one, because it materially changes the budget.

The fees that must be in every quote

Every loft conversion, without exception, needs a structural engineer's calculations for Building Control, covering the floor beams, ridge beam and any dormer or gable structure. Those fees start from around £395 and should be a fixed price agreed before work begins.

Building Regulations approval applies to every conversion too, whether or not you need planning permission. Fire safety is the big one here: adding a habitable floor means the whole house needs a protected escape route, usually fire doors and mains-linked alarms across every level. These aren't optional extras to trim, they're part of the real cost.

Region, and why London costs more

Location shifts the whole scale. London and the South East typically run 20 to 45 percent above the national average, because labour, access and scaffolding all cost more in the capital.

So a dormer that's £45,000 in a northern town can be £65,000 or more in London for the same specification. When you read a national average, adjust it upward if you're in the South East, and treat any quote well below the regional band with suspicion rather than delight.

Getting a figure you can trust

The reason quotes on the same house can vary by £20,000 is almost always that someone skipped the survey or the structural stage. A defensible quote comes after a proper look at your roof, your head height and the structural design, not before.

So the sensible order is to confirm your roof type, get the head height measured, and have the structure assessed, then price the specific scheme rather than a generic average. Do that, and the wide, scary range at the top of this article narrows to a firm number you can actually plan around, one that reflects your roof rather than someone else's.