What is a hip to gable loft conversion?
A hipped roof slopes down on all sides, including the ends. The sloping end (the hip) eats into the loft, so there is often not enough headroom to use it. A hip to gable conversion builds the end wall of the house straight up to the ridge and extends the ridge across, so the loft gains a full-height end wall and a much bigger usable floor.
It only works where the roof has a hipped end to convert, so it is mostly seen on semi-detached, end-of-terrace and detached houses and on some bungalows. Some owners combine it with a rear dormer to gain headroom across the back of the loft as well; this is often called a hip to gable and rear dormer conversion.
Do you need planning permission for a hip to gable loft conversion?
Often not. Roof enlargements fall under Class B of the householder permitted development rules. The Planning Portal lists the limits and conditions, and the government's technical guidance explains how councils read them. If your project meets all of them, you do not need to apply for planning permission.
You will need a householder planning application if any of these apply:
- the property is a flat, or a building containing flats
- the house is on Article 2(3) designated land: a conservation area, an Area of Outstanding Natural Beauty, a National Park, the Broads or a World Heritage Site
- permitted development rights have been removed for your house or area
- the house was created under certain other permitted development rights (for example a change of use to a house, or extra storeys already added under permitted development)
- the design breaks one of the Class B limits below
Our guide to householder planning applications covers fees, forms and what happens after you apply.
The permitted development rules that apply
These are the Class B limits and conditions from the Planning Portal and the technical guidance, with what each means for a hip to gable design:
- Volume: the enlarged roof space must not exceed the original roof space by more than 40 cubic metres for a terraced house or 50 cubic metres for any other house. Any previous roof enlargement counts towards this, including a rear dormer built at the same time or earlier.
- Height: the new roof must not be higher than the highest part of the existing roof. A new gable is built up to the existing ridge, not above it.
- Front roof slope: the work must not extend beyond the plane of the existing roof slope on the principal elevation where it fronts a highway.
- Materials: exterior materials must be of a similar appearance to the existing house. The technical guidance says they do not need to be the same materials or match exactly.
- No balconies: verandas, balconies and raised platforms are not allowed. A Juliet balcony with no platform would normally be permitted development, according to the government guidance quoted by the Planning Portal.
- Chimneys, flues and pipes: Class B does not cover installing, altering or replacing a chimney, flue or soil and vent pipe.
- Side windows: any window in a wall or roof slope forming a side elevation must be obscure-glazed and non-opening, unless the opening parts are more than 1.7 metres above the floor. The new gable wall is a side elevation, so a clear, openable window there would not meet this condition. The guidance says obscure glazing should be at least level 3, and one-way glass does not count.
Two rules that do not apply to a hip to gable
Class B normally requires the eaves of the original roof to be kept or reinstated, and any enlargement to be set back, so far as practicable, at least 20cm from the original eaves. The Planning Portal states that these two points do not apply to the relevant parts of any hip to gable enlargement. The government's technical guidance says the same: the eaves and set-back condition applies other than in the case of a hip to gable enlargement. The exemption covers only the relevant parts of the hip to gable work, so a rear dormer added at the same time still needs to meet the eaves and set-back conditions.
The volume trap for end-of-terrace houses
The technical guidance defines a terrace house as a house in a row of three or more houses used or designed as single dwellings, and it says a house at the end of a row counts if it shares a party wall with a house in that row. So an end-of-terrace house is a terrace house for Class B purposes and gets the lower 40 cubic metre allowance, not the 50 cubic metres a semi-detached or detached house gets. A hip to gable plus a full-width rear dormer can use up a lot of volume, so it is worth calculating the figure from measured drawings rather than estimating it.
The calculation is made against the original roof space. The guidance treats the original house as it stood on 1 July 1948, or as it was built if it is newer, so a roof extension added by an earlier owner still counts against the allowance.
Building regulations, party walls and an LDC
Building regulations: the Planning Portal says building regulations approval is required to convert a loft into liveable space, whether or not planning permission is needed. It is a separate process from planning. Our post on planning drawings versus building regulation drawings explains the difference.
Party walls: GOV.UK says you must tell your neighbours if you want to carry out building work near or on your shared property boundary. If your loft work affects a wall you share with a neighbour, check the party wall guidance early.
Lawful development certificate: you do not need a certificate to build under permitted development, but you can apply for one. Once granted, a proposed development carried out in line with it is presumed lawful unless there is a material change before work starts, such as an Article 4 direction removing the relevant permitted development right, according to GOV.UK. It does not replace building regulations approval. Our lawful development certificate guide covers when one is worth getting.
What we check first
Before we advise on any loft, we ask the homeowner for a few phone photos: the rear roof slope, the front of the house from the street, and a wider shot showing the neighbours' roofs on either side. We also ask which kind of loft they have in mind, such as a rear dormer, a hip to gable or a front dormer. The wider photo helps us see the roof shape of the pair or the row, which matters for the volume and for which route applies.
Some homeowners come to us after being told their loft would not be allowed. In those cases we take a second look at the route: whether the design can be brought within the permitted development limits, or whether a householder application is the better path. For a wider look at loft rules, including dormers and rooflights, see do you need planning permission for a loft conversion.
Frequently asked questions
Is a hip to gable loft conversion permitted development?
It can be. It falls under Class B, so it is permitted development if it stays within 40 cubic metres (terraced houses, including end-of-terrace) or 50 cubic metres (other houses), uses materials of a similar appearance, does not go above the existing roof, does not extend beyond the front roof slope where it faces a highway, has no balcony, and meets the side-window condition. Flats and houses on designated land need planning permission.
Can I combine a hip to gable with a rear dormer?
Yes. Both parts count towards the same volume allowance, and the hip to gable exemption does not extend to the dormer, so the dormer must still meet the eaves and 20cm set-back conditions.
Can I put a window in the new gable wall?
Under permitted development, a window in the side gable must be obscure-glazed and fixed shut, unless the opening parts are more than 1.7 metres above the floor. A clear, openable side window would need planning permission.
Do I need building regulations approval?
Yes. Building regulations approval is required to turn a loft into liveable space, even when no planning application is needed.
Do I need a lawful development certificate?
You do not need one to build under permitted development, but it gives you a formal decision from the council that the proposed work is lawful before you build.
Talk it through with us
If you are weighing up a hip to gable loft and want to know which route applies to your house, book a free advice call. Send us a few photos of your roof and we will tell you what we see.
