Hip to Gable Loft Conversion: Simple UK Guide for Homeowners
A hip to gable loft conversion changes the shape of your roof to create more usable space. It’s a popular upgrade for families who want an extra bedroom, bathroom, or home office without moving house.
This guide explains everything in simple language regarding house extension design and structural requirements. You’ll learn the costs, planning rules, structural work, and whether your home is suitable.
What Is a Hip to Gable Loft Conversion?
A hip to gable loft conversion changes a sloping roof edge (the “hip”) into a straight vertical wall (the “gable”). This creates more headroom and a wider floor area inside the loft.
How the roof shape changes
Most hipped roofs slope down on three sides. When you extend the hip upward into a straight wall, you replace that angled side with a flat gable wall. This unlocks a chunk of extra space.
Why it adds more usable space
The new vertical wall removes the awkward narrow section of the loft. That space becomes part of the main room instead of being dead space.
Homes that suit this conversion
A hip to gable conversion is best for:
- Semi-detached homes
- Detached homes
- End-terrace houses
Mid-terrace houses don’t have a hipped side, so they’re not suitable.
When Is a Hip to Gable Conversion a Good Choice?
It’s a strong option if:
- Your loft has low headroom.
- You want a full-size bedroom with an en-suite.
- You need more floor space than a simple dormer can offer.
- You already plan to add a rear dormer.
Many homeowners combine hip to gable with a rear dormer loft conversion to create a large master suite.
How Much Does a Hip to Gable Loft Conversion Cost in 2026?
For a detailed breakdown, see our full loft conversion cost guide.
Build Costs
A typical hip to gable loft conversion costs: £50,000 to £75,000 (2026 UK average)
If combined with a rear dormer: £60,000 to £85,000
Structural Engineering & RSJ Design
Most projects require:
- RSJ steel beams
- Floor strengthening
- New gable wall support
- Roof load redistribution
Steel beams for loft conversions carry the weight of the new roof and floor.
Typical engineer fees: £450 to £900 depending on complexity.
Extra Costs
- Stairs: £2,500–£4,500
- Insulation: £1,000–£2,000
- Fire-safe doors: £300–£700
- En-suite fitting: £6,000–£10,000
Planning Permission vs Permitted Development
When planning is required
You may need planning permission if:
- You live in a conservation area
- Your house has already used its volume allowance
- You want to raise the ridge height
- You want a design that changes the house front
Permitted development rules
Most hip to gable loft conversions fall under permitted development if:
- The total loft extension stays within the 50m³ allowance (40m³ for terraces)
- Materials match the existing house
- The new gable doesn’t overhang the boundary
Your builder still needs Building Control approval. For official rules, refer to the Planning Portal guidance.
Structural Work Involved
A hip to gable conversion requires proper structural design.
New gable wall
The old hipped section is removed and rebuilt as a vertical gable. This involves new brickwork, cavity insulation, and wall ties.
RSJ beams and load paths
Steel beams carry the weight of the new roof and floor. Engineers design these to match your house layout. RSJ design is crucial here.
Floor strengthening
Most older lofts were never meant to support a bedroom. New joists or steels are added to create a safe floor. If you are also doing a load bearing wall removal on the floor below, this must be calculated together.
Roof supports
New rafters and purlins are installed to handle the changed roof shape.
Engineers perform structural calculations for all these elements.
Step-by-Step Process
Survey
A measured survey checks roof height, span, existing supports, and access.
Drawings
Architectural drawings show the new layout and external appearance.
Structural calculations
Engineers perform the steel beam calculation, load paths, and connections. These are submitted to Building Control.
Builders start work
The roof is opened, steels fitted, gable built, and the interior finished.
Building Control inspections
The inspector checks structural work, insulation, fire safety, and final completion.
Pros and Cons
Advantages
- Adds significant space
- Often allowed under permitted development
- Works well with a dormer
- One of the best value-for-money loft options
Limitations
- Not suitable for mid-terrace homes
- More expensive than a basic dormer
- Requires a strong structural design
Hip to Gable vs Dormer vs Mansard
| Type | Space Gained | Cost | Appearance |
|---|---|---|---|
| Hip to Gable | High | Medium-High | Matches existing house |
| Rear Dormer | Medium | Medium | Boxy look |
| Mansard | Very high | High-Very high | Planning needed |
How Long Does It Take?
A hip to gable loft conversion usually takes: 6 to 10 weeks depending on weather, access, and layout.
Common Mistakes to Avoid
- Starting without proper structural design
- Poor insulation that fails Building Control
- Choosing the cheapest builder
- Not planning the staircase early
FAQs
What is a hip to gable loft conversion?
It changes a sloping roof into a vertical gable wall to create more space.
How much does it cost?
Typically £50,000 to £75,000 for the build, plus optional extras. Compare this to the cost of extensions generally.
Do I need planning permission?
Often no. Most fall under permitted development if volume rules are met.
Does it add value?
Yes. Many homes gain 15–20 percent in value after a good loft conversion.
Can it be done with a dormer?
Yes. This is the most common combination.
For specific advice, you may need a structural engineer for loft conversions. You can also use our beam calculator for preliminary checks.
Conclusion
A hip to gable loft conversion is one of the best ways to unlock extra space in a semi-detached or detached home. With the right design, good structural work, and proper planning, the loft becomes a bright and comfortable bedroom, office, or en-suite. A correct design is the first step on any successful loft conversion checklist.
Get Your Structural Drawings
If you want structural drawings and RSJ calculations for your project, you can contact SECalcs and get everything ready for Building Control. Whether you need a structural engineer Manchester, London or elsewhere in the UK, we can help.