Conversion types
Hip-to-gable loft conversions
A hip-to-gable extends a sloping hipped roof end out to a vertical gable wall, adding full-height floor area along that end. It is Permitted Development under Class B — subject to the same 40m³/50m³ volume cap and the designated-land exclusion — and typically consumes 15–25m³ on its own.
Last reviewed
What a hip-to-gable is
A hipped roof slopes inward on its end as well as its front and back, so the loft narrows to a point at that end. A hip-to-gable conversion extends the end wall up vertically to form a gable, and fills in the roof above it — turning a wedge of unusable space into full-height floor area running the depth of the house.
It is most often paired with a rear dormer: the gable gives you width at the end, the dormer gives you height across the middle, and together they turn a marginal loft into a proper double bedroom with an en-suite.
Which houses can have one
| House type | Hipped ends available | Notes |
|---|---|---|
| Mid-terrace | None | Party walls both sides — nothing to square off |
| End-of-terrace | One | The free end only, and on a 40m³ allowance |
| Semi-detached | One | The free end only, on a 50m³ allowance |
| Detached | Up to two | Both ends possible; doing both will usually exhaust 50m³ alone |
| Gable-ended house of any type | None | The end is already a gable |
The Permitted Development position
A hip-to-gable is an enlargement of the roof, so it sits under Class B and takes almost all of Class B with it:
- Volume counts. Against the same 40m³ / 50m³ cap, cumulative with everything else.
- Nothing above the ridge. The new gable is filled in to the existing ridge line, not above it.
- Materials must match. The new gable wall has to read as part of the house — usually brick or render to match, with the roof tiles carried across.
- Designated land still kills it. Class B is withdrawn in a Conservation Area, AONB or National Park, and a hip-to-gable is very visible from the street, so it is rarely a promising planning application in those areas either.
- The 200mm eaves setback does not apply. B.2(b) excepts hip-to-gable enlargements by name.
What it costs you in volume
The volume added is roughly the wedge between the old hip plane and the new gable plane — driven by the span of the hipped end, the roof pitch, and how far the hip is inset from the end wall. On a standard semi-detached house that comes out around 15–25m³.
On a 50m³ allowance that leaves 25–35m³ for a rear dormer, which is usually enough but not always comfortably. If you are planning both, the volume figure stops being a rule of thumb and starts being the thing the scheme lives or dies on — see the volume allowance in detail.
The structural consequence
A hip-to-gable is a bigger structural job than a dormer. The hipped end is a three-dimensionally braced structure; removing it and replacing it with a flat gable wall changes how the roof resists lateral load. The new gable needs to be tied back into the roof structure and carried down to a foundation capable of taking it, usually via the existing end wall.
This is not a detail to leave to site. It is the kind of thing a structural engineer decides before the scaffolding goes up, and getting it wrong is expensive in a way that a mis-sized dormer is not.
Common questions
- Can a terraced house have a hip-to-gable conversion?
- Only an end-of-terrace, and only at its one free end. A mid-terrace house has party walls on both sides and no hipped end to square off. Semi-detached houses have one free end; only a detached house can have a hip-to-gable at both ends, and doing both will usually exhaust a 50m³ allowance on its own.
- Does a hip-to-gable need the 200mm eaves setback?
- No. Class B.2(b) expressly excepts an enlargement consisting of a hip-to-gable from the 200mm setback requirement — a gable that stopped 200mm short of the eaves would be structurally and visually absurd. Every other Class B condition still applies.
- How much volume does a hip-to-gable use?
- Typically 15–25m³ on a standard semi-detached house, depending on roof pitch, the span of the hipped end and how far the hip is inset. It is a substantial share of a 50m³ allowance, which is why pairing one with a large rear dormer often runs close to the cap.
Sources
- GPDO 2015 — Schedule 2, Part 1, Class B — the roof-enlargement rules, including the 40m³/50m³ volume allowance
- Permitted development rights for householders: technical guidance — the government's plain-English reading of Class B, with diagrams
Check your own roof, free
Answer a few questions about your property and we will work through every Permitted Development condition against your actual dimensions.
Start the free assessmentFree to check. The £29 full report is fully credited against your full structural design.
Related guides
Rear dormer loft conversion rules
The Permitted Development limits that shape a rear dormer: volume, ridge height, the 200mm eaves setback, highway frontage, matching materials and side windows.
The 40m³ / 50m³ volume allowance, explained
How much roof volume Permitted Development lets you add, what 'original' means, why the allowance is cumulative, and how a rear dormer's volume is actually calculated.
Permitted Development rules for loft conversions
Class B and Class C of the GPDO 2015, explained clause by clause: volume limits, ridge height, eaves setback, highway frontage, materials and side windows.
Loft conversion head height
There is no legal minimum ceiling height for a loft room. 2.2m is a practical guideline, not a regulation — and the number that matters is the finished height after build-up.
Written by the LoftNow team from the legislation and Approved Documents cited above, and reviewed against the rules our assessment engine implements. It is general guidance for properties in England, not advice on your particular property — Permitted Development is self-assessed, and the definitive answer for a specific house comes from your local planning authority, normally via a Lawful Development Certificate.