What is a hip to gable loft conversion?
A hip to gable conversion replaces the sloping end of your roof with a flat vertical wall, so the loft gets taller and wider at that end. You need a sloping roof end to have one, which means a detached house, a semi, an end of terrace, a bungalow or a chalet.
What is the difference between a hip and a gable roof?
As with many roof varieties, the difference between a hip and gable roof lies in the shape of the structure.
Hip roofs
A hipped roof slopes on three or four sides, so the end of the roof leans inwards instead of rising to a wall. It is common on detached and semi detached houses and on bungalows.
Gable roof
A gable roof slopes on two sides. At each end, the wall rises straight up in a vertical triangle of brickwork, called the gable end. Most terraced houses have this kind of roof.
A quick way to tell is to look at the side of your house from the street. If the roof slopes away at the end, it is hipped. If the wall carries on up into a triangle, it is already a gable.
A hip to gable conversion takes a hipped end and builds it up into a vertical gable wall. The ridge is extended out to meet the new wall, which gives you the extra height and width in the loft.
Which houses can have a hip to gable loft conversion?
If your house has a hipped roof, and you are looking to increase the volume of your loft, you may be eligible to build a hip to gable conversion in your loft.
How tall is the loft now? Measure from the top of the loft floor joists to the underside of the ridge. Aim for about 2.1m to 2.2m before work starts, because the new floor and insulation take 200mm to 300mm of it.
What is holding your roof up? A roof built on site from rafters and purlins converts readily. A roof made from prefabricated W shaped trusses, common from the mid 1960s onwards, fills the loft with timber that cannot simply be cut away. It can still be done, but it needs a new floor and steel, and it costs more.
Where do the stairs go? The new staircase has to land somewhere with head height above it, and it usually takes space from the room below. On many houses this decides the whole layout, so sort it first. Generally speaking, aim to place the proposed stairs on top of the existing staircase.
One appearance point. On a street where every house still has its hipped end, removing this stands out. Not a planning objection if the work is permitted development, but worth a walk down the road first.
Not sure what your roof will allow? The Extension Potential Checker gives you a first read on what your property can take.
How much space does it actually add?
Less than people expect on its own, and a lot alongside a dormer.
On its own, it widens the usable part of the loft at one end. You gain a strip of full height space, usually enough to make one bedroom work properly rather than to create a second room.
That is why most projects are a hip to gable with a rear dormer. The hip to gable gives you width and head height at the end. The dormer gives you floor area across the back. Together they turn an awkward triangle into a proper room with usable space. If you take one thing from this page: price the two together, because that is what you are probably buying.
How much does a hip to gable loft conversion cost in 2026?
Hip to gable loft conversion cost by region 2026 · Cost excluding VAT
| Where you are |
Hip to gable |
With a dormer |
| London |
£45k–£55k |
£75k–£90k |
| Surrey |
£45k–£55k |
£75k–£90k |
| South East |
£43k–£53k |
£72k–£86k |
| South West |
£43k–£53k |
£72k–£86k |
| East |
£41k–£50k |
£68k–£82k |
| Midlands |
£39k–£48k |
£65k–£78k |
| North West |
£37k–£45k |
£62k–£74k |
| Wales |
£37k–£45k |
£62k–£74k |
| North East |
£35k–£43k |
£59k–£70k |
These figures are indicative first fix benchmarks based on construction tenders received through Resi. They are intended for early-stage budgeting only and should not be considered a quotation or guarantee of final construction costs. Actual costs will vary depending on project scope, specification, location, site conditions, contractor and prevailing market conditions.
Want a figure for your own house? The Build Cost Calculator puts your size, location and finish level against Resi's data.
What other costs should you consider?
Beyond the build itself, your total budget will depend on factors such as design fees, structural engineering, building control and VAT. You may also need to account for planning fees, party wall costs and interior finishes, depending on your property and project. These additional expenses should be factored into your overall loft conversion costs.
Pros and cons of a hip to gable loft conversion
Pros:
- Can be combined with rear dormer loft to maximise space
- Suitable for bungalows and chalets
- Can be done using permitted development rights
- Aesthetically pleasing, as it blends in with the existing home
Cons:
- Without permitted development rights, you may struggle with a semi detached property as it will remove symmetry
- Without a dormer extension, it may not be worth exploring
Do I need planning permission for a hip to gable loft conversion?
If you have permitted development rights, no. Roof enlargements are covered by Class B of the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended, which grants permission in law. Most hip to gable work on a house sits inside it.
However, you will need an application if your house is on designated land: conservation areas, National Parks, the Broads, National Landscapes (formerly areas of outstanding natural beauty) and World Heritage Sites. Class B is withdrawn completely here, so even rear facing work needs an application.
You will also need an application if:
- The extra roof volume is over the limit: 50 cubic metres on a detached or semi detached house, 40 on a terraced house
- The work is on the roof slope of your principal elevation and it fronts a highway
- Any part would sit higher than the highest part of your existing roof. A hip to gable normally keeps the ridge where it is, so this is usually fine. A design that lifts the ridge is not
- Your home is a flat or maisonette, or the house is listed
Am I in a conservation area? tells you how to check.
Conditions you still need to meet
Even when permitted development applies, the work must meet these conditions:
- Materials must be similar in appearance to the existing house
- Any window in a side-facing wall or roof slope, which includes the new gable wall, must be obscure-glazed. It must also be non-opening unless the opening part is more than 1.7m above the floor of the room
- If you add a dormer alongside the hip to gable, it must be set back at least 20cm from the original eaves, measured along the roof slope. This doesn’t apply to the hip to gable part itself
Get proof it was legal
Even if you don’t need an application, apply for a lawful development certificate. It gives you proof the work was legal, which buyers’ solicitors will ask for when you sell. An architect can also calculate your roof volume before you commit.
Hip to gable building regulations: what is required?
Building control sign off is needed for every loft conversion, including one that is permitted development. Permitted development is a planning route, not an exemption from building control. Different people, different rules.
See the building regulation cost breakdown for what the drawings, structural engineer, inspections and surveys cost.
Taking the hip off changes how the roof holds itself up. A hipped end braces the roof at the corner, and the purlins land on it. Remove it and the new gable wall has to do that job. Expect a gable in blockwork or timber frame, restraint straps tying it to the roof and floor, and steels where needed. This is why a structural engineer is not optional here.
Check what the new wall stands on. The gable is built off the existing flank wall, so that wall and its foundation have to take the extra load. Your engineer will confirm it. On some bungalows it needs work.
The floor has to be built, not borrowed. Your loft joists were sized to hold up the ceiling below, not people and furniture. A new floor structure goes in, usually deeper joists spanning onto new steels.
Fire safety shapes the design more than anything else. A two storey house becoming three storey changes what the regulations ask for. The staircase becomes a protected escape route, which normally means fire resisting doors onto it, upgraded floors, and mains powered interlinked alarms on every storey. This is why a loft conversion ends up touching rooms that have nothing to do with the loft.
The staircase has to be a proper one. Fixed, a maximum pitch of 42 degrees, with rules on each step. Loft conversions get a relaxation on headroom: where the full 2m cannot be achieved, 1.9m at the centre and 1.8m at the side is accepted.
Insulation, ventilation and windows. The new gable and altered roof have to meet the standards for work to an existing home. Rooms need background and purge ventilation. Where a bedroom opens onto a stair that is not fully protected, an escape window may be required.
Does the Future Homes Standard apply? No. It was published on 24 March 2026, comes into force on 24 March 2027, and sets standards for newly built homes. Work to an existing house sits outside it.
Keep the completion certificate. Building control sign off proves the conversion is legal, and it is the first thing a buyer's solicitor asks for. A loft room without one is hard to sell as a bedroom.
Resi's building regulations package covers the technical drawings and structural calculations your builder and building control will need. Get a quote.
