Hip-to-Gable vs Rear Dormer: Which Is Right for Your Hipped Roof?

What Is a Hip-to-Gable Loft Conversion?

A hip-to-gable conversion rebuilds the sloping end wall of a hipped roof into a vertical gable wall. This pushes the ridge outward and unlocks usable floor area from the side of the loft. That space would otherwise sit empty and unreachable behind the eaves.

The new gable is built in matching brick or render so it blends with the rest of the house. Crucially, this is structural work — you are changing the actual shape of the roof. As a result, a hip-to-gable conversion almost always needs building regulations approval, and it works best paired with a rear dormer to justify the effort.

These conversions suit 1930s semi-detached homes, 1960s detached bungalows, and any hipped-roof property where the loft is otherwise too cramped to convert. In practice, the hipped sides are the main thing holding the space back, so squaring one off makes a real difference.

What Is a Rear Dormer Loft Conversion?

A rear dormer adds a box-shaped, flat-roofed extension that projects straight out from the rear roof slope. It creates full standing headroom across the back of the loft. The result is a large, usable room that flows naturally into the existing space.

On a gabled roof, such as a Victorian terrace or Edwardian semi, a rear dormer alone often makes a full-size loft bedroom. On a hipped roof, however, a dormer on its own can feel narrow and awkward. That is because the sloping sides still pinch the width — which is exactly why pairing it with a hip-to-gable works so well.

The L-Shaped (Combined) Dormer: The Best of Both

The most popular fix for hipped-roof homes in London is to combine a hip-to-gable on one or both sides with a rear dormer at the back. This creates an L-shaped structure, or a U-shape on detached homes with two hip sides. The result is full-height headroom across nearly the entire loft floor.

This combination turns a dark, awkward attic into a genuinely spacious room. For example, you might fit a master bedroom with en-suite, a generous home office, or even two rooms split by a new internal wall. Better still, the layout feels like a proper part of the house rather than a tacked-on box.

The combined approach does cost more than either option on its own. That said, the cost per square metre of usable space is often better than doing each conversion separately at different times. You also avoid paying twice for scaffolding, surveys, and disruption.

Planning Permission for Hipped Roof Conversions

Most hip-to-gable conversions and rear dormers fall under Permitted Development on detached and semi-detached houses, so no planning application is needed. That covers the majority of hipped-roof homes. Even so, the rights come with firm conditions, and your conversion only qualifies if it meets all of them:

• The total volume added does not exceed 50m³ (detached/semi-detached)
• The conversion does not exceed the existing ridge height
• No dormer is on the front elevation
• The property is not in a conservation area or subject to an Article 4 direction
• The property is not a listed building

If your home sits in a conservation area, you can often still convert — but a planning application will usually be needed. The good news is that this is a routine hurdle, not a dead end. We check every planning constraint as part of each free survey, so you know where you stand before committing.

Cost: What to Expect in London

A standalone hip-to-gable conversion typically costs £32,000–£52,000 in London, while a rear dormer alone runs £28,000–£48,000. The combined L-shaped dormer is the most common choice for hipped-roof homes. It typically costs £42,000–£65,000, depending on the specification, size, and borough.

This is a significant investment, but the combined approach delivers far more usable space than either conversion alone. On top of that, the return on a London property is usually strong. Our hip-to-gable pricing guide breaks down the full cost, including structural calculations, planning checks, and building regulations.

Which Should You Choose?

For most hipped-roof homeowners who want a genuinely usable room, the combined L-shaped dormer is the right answer. A hip-to-gable alone rarely does enough, because you still need the rear dormer for the main headroom. A rear dormer on its own works too, but it leaves you with a narrower room.

Detached properties with two hip sides are the exception. Here, a full wrap-around approach — both sides converted plus a rear dormer — can create exceptional space. However, it costs more and demands careful structural design.

The best way to decide is to have a specialist look at your loft. During the free survey, we'll show you exactly what space each option achieves. After that, you'll get a fixed-price quote for every route, so you can compare them properly.