Hip to Gable Loft Conversion Cost 2026: Prices, Rules + Suitability
A hip to gable loft conversion costs £33,000–£70,000 in the UK in 2026 on its own, and £45,000–£80,000 when combined with a rear dormer — the design most homeowners order. London adds 15–20%. It replaces the sloping side (hip) of the roof with a vertical gable wall, widening the loft to the full width of the house and turning a semi's cramped roofspace into a full bedroom floor.
The hip to gable is the middle band in our loft conversion cost guide, above a rear dormer and below a mansard, and the natural choice for the UK's millions of hipped-roof 1930s semis.
What is a hip to gable loft conversion?
A hip to gable loft conversion changes the shape of a hipped roof — one that slopes inward on the side as well as the front and back — by building the side wall of the house straight up to the ridge and extending the roof over it, creating a vertical triangular gable end. The loft gains the full width of the house at full height where the hip used to cut the ceiling down to nothing.
A dormer adds a box to the roof; a hip to gable changes the roof itself. The two are combined on most hipped semis because the gable widens the loft while the rear dormer deepens it, and the combined floor fits a double bedroom, en-suite and a landing with room for a compliant staircase.
How much does a hip to gable loft conversion cost?
A hip to gable loft conversion costs £33,000–£70,000 in the UK in 2026 as a standalone job, and £45,000–£80,000 with a rear dormer added, per Checkatrade and MyJobQuote's 2026 guides. MyBuilder's widely quoted £50,000–£70,000 UK and £55,000–£75,000+ London figures describe the combined build, which is why they sit above the standalone band.
| Scope | UK cost (2026) | London cost (+15–20%) | What you get |
|---|---|---|---|
| Hip to gable only | £33,000 – £70,000 | £38,000 – £84,000 | Full-width loft, new gable wall, floor steels, stair, insulation, rooflights; one large bedroom |
| Hip to gable + rear dormer | £45,000 – £80,000 | £52,000 – £96,000 | Widened and deepened loft; double bedroom + en-suite with full-height rear wall and windows |
The gable wall material moves the price most within each band: matching reclaimed brick on a 1930s semi costs £4,000–£7,000 for the gable triangle; render or tile-hanging over blockwork costs £2,500–£4,500. A double hip to gable on a detached house sits at the top of the standalone band because two gables and a full-length new ridge are built.
Which houses suit a hip to gable loft conversion?
Hipped-roof semi-detached, end-of-terrace and detached houses and bungalows suit a hip to gable conversion; mid-terrace houses do not — they already have gable party walls on both sides. The 1930s semi is the archetype: a hipped roof, a cut-rafter structure that converts without trussed-rafter surcharges, and 2.4m+ at the ridge.
| House type | Roof | PD volume cap | Party wall notices | Usual design |
|---|---|---|---|---|
| Semi-detached (1930s onward) | Hipped on the open side | 50m³ | 1 | Hip to gable + rear dormer |
| End-of-terrace | Hipped on the open side | 40m³ | 1 | Hip to gable alone, or with a small rear dormer |
| Detached | Hipped both sides | 50m³ | 0 | Double hip to gable, or single gable + rear dormer |
| Bungalow | Hipped, low pitch common | 50m³ | 0 | Hip to gable + rear dormer; raise-the-roof route where ridge is under 2.2m |
| Mid-terrace | Gabled already | 40m³ | 2 | Not applicable — rear or L-shaped dormer instead |
Two gates apply. Head height needs 2.2m from joist top to ridge; bungalows with shallow 1960s–70s roofs often fail, and their route is raising the roof to a full storey at £75,000–£150,000+ (MyJobQuote/Rated People 2026), not a hip to gable. Post-1965 trussed-rafter roofs add £5,000–£10,000 of steel to replace the W-shaped trusses. Our 1930s house loft conversion guide covers why that decade's roofs are the easiest of all.
Hip to Gable Loft Conversion Cost Calculator
The calculator applies the two scope bands from the cost table to your house type, finish and region; detached houses run higher because both hips are rebuilt or the spans are longer. Results round to the nearest £500 and exclude the items under the result.
House type, scope and finish for a 2026 range.
Do I need planning permission to change my roof from hip to gable?
Usually not. A hip to gable conversion is permitted development under Class B of the Planning Portal's householder rules provided the added roof volume stays under 50m³ on a semi-detached or detached house, or 40m³ on an end-of-terrace, the new gable rises no higher than the existing ridge, and the materials are similar in appearance to the existing house. A Lawful Development Certificate (£129) proves it at sale.
The volume cap is shared between the gable and any dormer — where hip to gable projects get caught. The gable consumes 15–25m³ on a typical semi; a full-width rear dormer takes 25–35m³ more. The combined 40–60m³ sits either side of a semi's 50m³ line, so the dormer is often trimmed to fit. On an end-of-terrace with a 40m³ cap, a gable plus a full dormer exceeds permitted development and needs a planning application (£528 householder fee, England).
| Element | Typical volume added | Semi / detached (50m³ cap) | End-of-terrace (40m³ cap) |
|---|---|---|---|
| Hip to gable alone | 15–25m³ | Permitted development | Permitted development |
| Hip to gable + small rear dormer | 30–45m³ | Permitted development | Borderline — measure before design is fixed |
| Hip to gable + full-width rear dormer | 40–60m³ | Borderline — trim the dormer to fit | Planning application |
| Any design in a conservation area or Article 4 street | — | Planning application | Planning application |
Conservation areas remove permitted development for roof enlargements, and a hip to gable changes the side elevation — the part conservation officers look at hardest on a street of matching hipped semis. Expect refusal where yours is the first gable in the row, approval where neighbours already have one. Side-facing windows in the new gable must be obscure-glazed and non-opening below 1.7m.
How can I convert my hip roof to a gable loft?
A hip to gable conversion is built by stripping the hip end of the roof, building the side wall of the house straight up to ridge height, extending the ridge to meet the new gable, re-covering the roof and then fitting the loft out. The sequence, from scaffold to completion certificate:
- Scaffold the side and rear, strip tiles and hip rafters from the sloping side.
- Build the gable — blockwork inner leaf with a brick outer leaf in matching stock, or blockwork rendered or tile-hung to match the house. The wall is tied into the existing side wall and the new floor structure.
- Install the steel ridge beam, extend the ridge and rafters to the gable, re-tile. The rear slope is either re-covered as it was or opened for the dormer box.
- Floor steels bear into the party wall (semi and end-of-terrace) and the new gable; new joists span between them.
- Staircase, insulation to Part L, first and second fix, then the building control completion certificate.
The gable brickwork decides whether the conversion looks right: insist on a brick sample against the existing wall before the wall goes up — a mismatched gable is visible from the street for the life of the house.
Hip to gable vs rear dormer: which adds more space?
A hip to gable plus rear dormer adds more space than either alone — 30–40m² of full-height floor on a typical semi, against 20–30m² for a rear dormer only and 15–25m² for a hip to gable only. On a hipped roof the dormer alone leaves the sloping hip cutting into one side of the room, which is why the combination dominates.
| Type | UK cost (2026) | What changes | Full-height floor gained (semi) | Planning |
|---|---|---|---|---|
| Velux / rooflight | £25,000 – £40,000 | Nothing — windows in the existing slope | 10–20m² on a hipped roof | Permitted development |
| Rear dormer only | £30,000 – £65,000 | Box added to rear slope; hip remains | 20–30m² | Permitted development |
| Hip to gable only | £33,000 – £70,000 | Side hip becomes vertical gable | 15–25m² | Permitted development |
| Hip to gable + rear dormer | £45,000 – £80,000 | Both — widened and deepened | 30–40m² | Permitted development within 50m³ |
How long does a hip to gable loft conversion take?
A hip to gable loft conversion takes 10–12 weeks on site alone and 10–14 weeks with a rear dormer, plus 4–8 weeks for structural design, building control approval and the party wall process. The gable brickwork adds a fortnight over a plain dormer — wet trade work that waits on weather. Scaffold stays up for the full build, blocking the side access path, so agree that with the neighbour early. Home Renovation Guides' timeline data shows the party wall notice, not the build, is the usual cause of a late start: serve it two months before steel is booked.
What is the cheapest way to convert a loft?
A Velux (rooflight) conversion at £25,000–£40,000 is the cheapest way to convert a loft, because the roof keeps its shape and the work is floor steels, insulation, a staircase and windows. On a hipped roof it disappoints: the hip slopes in from one side and leaves a strip of usable floor 2–3m wide. The cheapest conversion that produces a full-width room on a hipped semi is the hip to gable at £33,000–£70,000. £20,000 buys neither — sub-£30,000 quotes on a hipped roof have left out the gable, the stair or building control.
What is the 10 year rule for loft conversion?
The 10 year rule makes a planning breach immune from enforcement 10 years after the work was substantially completed. A hip to gable built without permission in a conservation area more than a decade ago cannot be ordered back to a hip. The paperwork gap remains at sale: buyers' solicitors ask for a Lawful Development Certificate for existing use (£129) with dated evidence, or an indemnity policy (£20–£100). Building regulations breaches never time out, so an uncertified gable wall or floor structure from any year needs a regularisation application. Home Renovation Guides' advice: use the rule to fix an inherited problem, never to plan a new one.
Related loft conversion guides
- Semi-detached loft conversion cost — the 50m³ cap, one party wall and the hip-plus-dormer default
- 1930s house loft conversion — why that decade's cut roofs and high ceilings convert best
- End-of-terrace loft conversion — hipped side, one neighbour, but a 40m³ cap
- Detached house loft conversion — double hip to gable and zero party walls
- Bungalow loft conversion cost — hip to gable versus the raise-the-roof route
- Dormer loft conversion cost — the rear dormer that pairs with the gable
Frequently asked questions
How much does a hip to gable loft conversion cost?
£33,000–£70,000 alone, £45,000–£80,000 with a rear dormer (UK, 2026). London +15–20%. MyBuilder's £50k–£70k figure is the combined build.
Do I need planning permission to change my roof from hip to gable?
Usually not — permitted development within 50m³ (semi/detached) or 40m³ (end-of-terrace), no higher than the ridge, matching materials. Conservation areas and Article 4 streets need permission.
How can I convert my hip roof to a gable loft?
Strip the hip, build the side wall up in matching brick or render to a gable, extend the ridge, re-cover, then floor steels, stair, insulation and fit-out under building control.
What is the cheapest way to convert a loft?
A Velux conversion at £25,000–£40,000 — but on a hipped roof it leaves a narrow strip of floor. The hip to gable at £33,000+ is the cheapest full-width option.
What is the 10 year rule for loft conversion?
Planning breaches become immune from enforcement 10 years after completion. Building regulations breaches never do. Fix paperwork with a £129 LDC or indemnity policy.
Can you do a loft conversion for 20k?
Not a hip to gable — it starts at £33,000. £20,000 is a basic Velux budget outside London on a roof without a hip.
Which lofts cannot be converted?
Under 2.1m to the ridge, no landing space for a compliant stair, or a flat without freeholder consent. Hipped roofs convert — the gable fixes the side head height.
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