Quick Answer: A dormer loft conversion adds a box-shaped extension to the rear roof slope and suits most terraced and semi-detached homes. A hip to gable conversion rebuilds the sloping side of the roof into a vertical wall and only works on houses with a hipped roof. Many semi-detached owners combine the two for the most usable floor space.
If you are adding a bedroom or a home office without giving up any garden, the loft is usually the first place to look. The hard part is choosing the right type. This guide compares the two most common UK options, explains the planning rules in plain terms, and shows what a real West London builder charges. For the general process of picking a firm, our guide on how to hire a general contractor covers the basics that apply on both sides of the Atlantic.
Table of Contents 1. What Is a Dormer Loft Conversion? 2. What Is a Hip to Gable Loft Conversion? 3. Side-by-Side Comparison 4. What Does Each Option Cost? 5. Planning Permission and Building Regulations 6. Which Houses Suit Which Conversion? 7. How to Choose a Loft Conversion Builder 8. FAQs
What Is a Dormer Loft Conversion?
A dormer is a structural box that projects out from the existing roof slope, usually at the rear. It creates vertical walls and a flat ceiling where there was only sloping rafter space before, which turns an awkward triangle into a room you can stand up in from wall to wall.
Dormers are the most popular loft conversion in the UK because they work on almost every roof shape: terraced, semi-detached and detached. A full-width rear dormer typically gives room for a double bedroom plus an en suite. Variations include the L-shaped dormer (common on Victorian terraces with a back addition) and the smaller pitched-roof dormer used where planners want a softer look.
Uxbridge firm Raaz Constructions Limited explains the build stages, steel work and finish options in detail on its dormer loft conversion page, which is worth reading before you ask for quotes.
What Is a Hip to Gable Loft Conversion?
A hipped roof slopes down on the side as well as the front and back. In a hip to gable conversion, the builder removes that side slope and builds the end wall straight up to the ridge, creating a vertical gable. The loft gains a full-height side section and a longer, more usable floor.
This option only works on homes that have a hipped side, which in practice means most 1930s semi-detached houses, detached houses and end-of-terrace properties. It is often paired with a rear dormer, a combination that gives the largest loft room short of a mansard. You can see how the work is staged on the hip to gable loft conversion page from Raaz Constructions.
Side-by-Side Comparison
| Factor | Dormer | Hip to Gable |
|---|---|---|
| Roof type needed | Almost any pitched roof | Hipped roof only |
| Typical homes | Terraced, semi-detached, detached | 1930s semis, detached, end of terrace |
| Extra headroom | Rear of loft | Side of loft and staircase area |
| Typical result | Bedroom plus en suite | Larger bedroom, better stair position |
| Often combined with | L-shape or Velux windows | Rear dormer |
| Planning permission | Often permitted development | Often permitted development |
| Build time | Around 6 to 8 weeks | Around 7 to 10 weeks |
Build times vary with access, steel delivery and weather, so treat these as typical ranges, not promises.
What Does Each Option Cost?
UK loft prices are usually quoted as a fixed project price, not as a percentage mark-up the way many US contractors work (we break that model down in how much does a general contractor cost).
As a real reference point, Raaz Constructions publishes its West London pricing openly:
| Conversion Type | Published Price Range (2026) | Source |
|---|---|---|
| Dormer loft conversion | £45,000 to £75,000 | Raaz Constructions |
| Hip to gable loft conversion | £50,000 to £75,000 | Raaz Constructions |
The final figure depends on floor area, whether you add an en suite, the stair design, window choice and how much steel the structural engineer specifies. Always get the price in writing with a clear list of what is and is not included. Our guide to comparing contractor bids shows how to line quotes up fairly.
Planning Permission and Building Regulations
Many loft conversions in England fall under permitted development, which means no full planning application is needed. According to the Planning Portal loft conversion guidance, the main limits are:
- Extra roof volume of up to 40 cubic metres for terraced houses and 50 cubic metres for semi-detached and detached houses
- No extension beyond the existing roof slope on the side facing the highway
- No part higher than the highest part of the existing roof
- Materials similar in appearance to the existing house
- Side-facing windows obscure-glazed and non-opening below 1.7 metres
Permitted development rights do not apply in conservation areas and can be removed by the council, so always check first. A Lawful Development Certificate is the safest way to prove your loft is allowed.
Building Regulations approval is required for every loft conversion, regardless of planning. It covers structure, fire escape routes, insulation, stairs and sound. If your loft work affects a shared wall, the Party Wall Act requires you to notify your neighbour in advance.
Which Houses Suit Which Conversion?
| Your House | Best Option |
|---|---|
| Mid-terrace with gable ends | Rear dormer |
| Victorian terrace with back addition | L-shaped dormer |
| 1930s semi-detached with hipped roof | Hip to gable plus rear dormer |
| Detached with hips on both sides | Double hip to gable or dormer |
| Bungalow | Dormer or hip to gable, depending on roof |
Local housing stock matters. In areas like Ickenham, many homes are interwar semis with hipped roofs, which makes hip to gable work common; Raaz covers those local planning details on its loft conversion Ickenham page. In Southall, where terraced streets dominate, rear dormers are the usual choice, as shown on the Southall loft conversion page.
How to Choose a Loft Conversion Builder
A loft conversion is structural work, so the builder matters more than the design. Before you sign:
- Ask for addresses of finished lofts you can view or photos of completed projects.
- Check that the quote includes structural calculations, Building Control fees and party wall costs, or lists them as extras.
- Ask who manages the build and which trades are subcontracted. Our article on general contractor vs subcontractor explains why this matters.
- Confirm insurance and any written guarantee. See how to verify a contractor’s licence and insurance for what to ask.
- Get a stage payment schedule tied to finished work, not dates.
As an example of what to look for, Raaz Constructions Limited in Uxbridge has been converting lofts across West London since 2012, has completed more than 350 projects, and offers a 5-year structural guarantee. Their main loft conversion services page compares every loft type they build, including mansard and Velux options.
FAQs
Is a dormer or hip to gable conversion cheaper? A standalone rear dormer is usually the cheaper of the two. Hip to gable work involves rebuilding a side wall and part of the roof structure, so it typically costs more, and combining both adds further cost.
Do I need planning permission for a hip to gable loft conversion? Often not. Most hip to gable conversions fit within permitted development volume limits, but conservation areas, flats and houses with removed rights need a full application.
Can you do a hip to gable on a terraced house? Only on an end-of-terrace house with a hipped side. A mid-terrace has no hip to convert.
How long does a loft conversion take? Most dormer conversions take around 6 to 8 weeks on site, and hip to gable or combined builds take a little longer.
Can I live at home during a loft conversion? Usually yes. Most of the work happens through the roof via scaffolding, and the stair opening is the main point of disruption, often near the end of the build.
Final Thoughts
If your roof is hipped and you want the most space, a hip to gable with a rear dormer is hard to beat. If you live in a terrace or simply want a cost-effective extra bedroom, a rear dormer is the proven choice. Either way, check your permitted development limits early and choose a builder with a track record of finished lofts you can actually see.
