A hip-to-gable loft conversion replaces a sloping hip end with a vertical gable wall. It’s usually permitted development on detached and semi-detached houses. Here’s how it works.
A hip-to-gable loft conversion involves extending one or both hipped roof slopes at the end of the house to create a vertical gable wall. This creates more usable loft space and is often combined with a rear dormer. Under Part 1, Class B of the GPDO 2015, a hip-to-gable can be permitted development on a detached or semi-detached house if the resulting roof volume doesn’t exceed 50m³ (40m³ for terraced houses). Hip-to-gable loft conversions are NOT permitted development on terraced houses because the rules only permit roof alterations within the existing roof plane for terraces. They are also not PD on designated land (conservation areas, national parks, AONB) or on properties where the original roof line would be materially altered.
A hip-to-gable loft conversion is most common on detached and semi-detached houses with a hipped roof (where all four sides slope down to the eaves). The conversion works by:
The effect is to turn a hipped roof into a simpler gable-ended roof form, which significantly increases the headroom and floor area in the loft. For a semi-detached house, only one side can have the hip replaced with a gable — the party wall side retains its original form.
| Condition | Detail |
|---|---|
| Permitted house types | Detached and semi-detached houses only. Hip-to-gable is NOT PD on terraced houses. |
| Volume limit | 50m³ total roof enlargement for detached houses. 40m³ for semi-detached (though hip-to-gable is generally only done on detached). |
| Height | Must not exceed the highest point of the existing roof |
| Materials | Must match the appearance of the existing house |
| Overhangs | No overhang beyond the existing eaves line |
| Designated areas | Not permitted on designated land (conservation areas, national parks, AONBs, World Heritage Sites) — side-facing windows must be obscure glazed |
| Terraced houses | NOT permitted development — any roof alteration that changes the roof line requires planning permission on a terrace |
Planning permission is required for a hip-to-gable conversion in these situations:
For planning permission applications, key design considerations include the impact on the character of the street (the gable end may be visible from the road on corner plots) and the relationship to the adjoining semi-detached house.
| Item | Approximate Cost |
|---|---|
| Hip-to-gable conversion (no dormer) | £15,000–25,000 |
| Hip-to-gable plus rear dormer | £35,000–55,000 |
| Hip-to-gable plus rear dormer with en-suite | £45,000–70,000 |
| Structural engineer fees | £1,500–3,000 |
| Party wall surveyor (if semi-detached) | £1,000–2,500 |
| Building regulations | £500–1,000 (building control fees) |
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