Hip-to-Gable Loft Conversion Cost Calculator
A hip-to-gable builds the sloping hip end up into a flat gable wall, turning an unusable triangle into full-height floor. It only applies to semis, end-terraces and detached houses with a hipped roof — a mid-terrace has no hip to build out.
Open the calculator →Price your hip-to-gable in 30 seconds
4 steps. Scope, staircase route, en-suite and region.
How this calculator works
A hip-to-gable takes the sloping end of the roof and builds it up into a vertical gable wall. The triangle of dead space at the hip end becomes full-height floor, which is why it usually produces more usable room per pound than a dormer alone on the same house.
The calculator prices gable-only and gable-plus-dormer separately because the combination is what most people actually build, and quoting the gable alone understates what a real project costs.
On the party wall: if the gable rises on the boundary, the Party Wall etc. Act 1996 applies. Two months notice, and a surveyor if your neighbour dissents. Budget for it rather than discovering it in week three.
Hip-to-gable cost by scope (2026)
| Option | Typical 2026 cost | Notes |
|---|---|---|
| Gable wall only | £42,000–£52,000 | No dormer |
| Gable plus rear dormer | £52,000–£65,000 | The usual combination |
| Gable, dormer and two rooms | £60,000–£68,000 | Wide detached |
| Cost per m² | £1,800–£2,500 | Between dormer and mansard |
| Party wall award, if needed | £900–£2,000 | Where the gable is on the boundary |
| Winder or quarter-turn stair | +£2,000–£4,000 | Where the landing is tight |
| En-suite, stack reachable | +£4,000–£7,000 | Rises sharply if it is not |
Figures match our hip-to-gable cost guide. A party wall award is a separate cost and a separate surveyor.
What changes a hip-to-gable quote the most
The gable wall is the extra work. A hip-to-gable takes the sloping hip end of the roof and builds it up vertically in blockwork or matching brick to the ridge, turning an awkward triangular loft into a usable rectangular room. That masonry — plus matching the existing brick or render so the new gable does not read as an afterthought — is the cost a plain dormer never carries, and it is why most hip-to-gable jobs also add a rear dormer to win head height where the roof still slopes.
Party wall comes next. A hip-to-gable on a semi almost always builds up off the shared boundary, so the Party Wall etc. Act 1996 applies and you will need a signed agreement, usually with a surveyor acting for each side. Serve the notice early: the two-month period runs whether or not the build has started.
After that it is the usual loft levers — where the new staircase lands, whether you add an en-suite, and whether the waste can reach an existing soil stack. If you are weighing a hip-to-gable against a plain box dormer on the rear, price both with the dormer calculator.
Hip-to-gable calculator FAQs
Only one with a hipped roof — a sloping end rather than a vertical gable. That means semis, end-terraces and detached houses. A mid-terrace already has gables on both sides, so there is nothing to build out.
If the new gable wall sits on or against the boundary with next door, yes. Serve notice at least two months before work starts. An agreed surveyor typically costs £900–£2,000 and it is not optional — building without an award leaves you exposed if anything cracks.
Almost always. The scaffolding is up, the roof is open and building control is already involved, so the dormer costs far less added to a hip-to-gable than it would as a separate job later.
Usually not on a house, within the volume allowance. Flats and maisonettes have no permitted development rights at all, and conservation areas often remove them.
Related cost guides
- Loft conversion costs — every type priced
- Planning permission — the PD volume limits
- Loft conversion quotes — 3 free quotes