Hip to Gable Loft Conversion Cost in London: 2026 Prices and Feasibility

Last updated: 6 November 2026

See it for your own home: put in your address and get free concept drawings and an indicative price. Get my free concept → Or see our Loft Conversions →

A hip to gable conversion replaces the sloping, hipped end of a roof with a vertical gable wall, built in line with the existing flank. It unlocks the side of a loft on a house whose roof falls away at one end — usually a semi-detached or detached house with a hipped roof. On its own it adds volume; with a rear dormer it produces a usable room.

In 2026 we publish £2,000–£2,800 per m² including VAT, or £70,000–£98,000 for 35 m² nationally, and London carries our published 30–50% premium. The bands sit in our loft conversion cost guide, and the loft conversion cost calculator gives a London floor-area range from the same published rates.

Table of Contents

1. What it is
2. Which houses suit it
3. Why it needs a dormer
4. Cost in London
5. Structure and party wall
6. Planning position
7. Compared with a dormer
8. How long it takes
9. Cost drivers

What a Hip to Gable Conversion Is

A hipped roof slopes inwards on all four sides, so at each end the roof falls away instead of ending in a wall. A hip to gable removes that hip and builds a vertical gable flush with the outside face of the flank wall — turning the dead triangle at the end of the roof into full-height headroom. It changes how the house looks from the side, which is why exterior work must use materials of similar appearance.

Which House Shapes Suit It

It is a conversion for hipped roofs: in London most often 1930s semi-detached and inter-war detached houses. An end-of-terrace house can have a hipped end; a mid-terrace usually has a gable already. Headroom comes second: our guide notes a comfortable conversion needs at least 2.2 m at the highest point.

Why It Usually Needs a Rear Dormer

A hip to gable alone adds volume at the end but leaves central headroom governed by the existing pitch, so it often still does not give a compliant stair arrival and a usable room. It is designed as a pair: hip to gable for volume and headroom, rear dormer for floor area and light. The allowance is measured on the resulting roof space including any previous enlargement, so do the arithmetic before fixing the design.

What a Hip to Gable Conversion Costs in London

Our published national band is £2,000–£2,800 per m² including VAT — £70,000–£98,000 for the 35 m² example the guide uses. London carries the published 30–50% premium, so budget above that band. We publish no London total and have not invented one; the closest comparison is the London band by floor area.

Structural and Party Wall Implications

The structural work is why this costs more per m² than a straight dormer. The hip rafters come out, a new gable frame or masonry wall goes in, and the junction with the existing roof has to be tied and weatherproofed. A structural engineer's input is normal — published at £500–£2,000.

On a semi-detached house the flank wall is often the party wall, which triggers the Party Wall etc. Act 1996: a party structure notice at least two months before work begins, and excavation notices at least one month where work goes within 3 m of a neighbour's structure and deeper than their foundations, or within 6 m and below the 45-degree line from their foundations. Our guide publishes £700–£2,000 for an agreement (party wall agreement cost) and £1,000–£3,000 for scaffolding.

Planning: the Permitted Development Position

A hip to gable is a roof addition, so the house permitted-development rules apply. They expressly contemplate this type: the requirement to keep the edge of the enlargement 0.2 m back from the existing eaves is disapplied for a hip to gable. The rest of the class still applies — no part above the highest existing part, so the ridge cannot be raised; no more than 40 m³ of additional roof space for a terrace or 50 m³ otherwise; no extension beyond the plane of a roof slope forming the principal elevation that fronts a highway; similar materials; side windows obscure-glazed and non-opening unless the openable parts are above 1.7 m; no balcony or raised platform.

Two things stop it being permitted development. On article 2(3) land — conservation areas, National Parks, areas of outstanding natural beauty — the class does not apply at all, so a hip to gable in a conservation area needs planning permission. And an Article 4 direction can remove the right. Our planning permission cost and timeline guide covers fees and decision times, and a lawful development certificate records the position formally. General information, not legal advice.

Hip to Gable vs a Straight Rear Dormer

The two are usually described as alternatives, but on a hipped roof they are more often a pair.

How Long It Takes

Our guide publishes 6–10 weeks of construction for a standard dormer, plus 4–8 weeks of design and planning. A hip to gable adds structural alteration and usually a party wall award, so allow longer for both stages.

What Drives the Cost

Two drivers are specific to this type: the structural alteration, since removing a hip and building a gable is more work than framing a dormer out of an existing slope; and the party wall, since on a semi the shared flank adds the notice and award process. Beyond that the published extras are the familiar ones — glazing at £800–£1,500 per roof window, a straight stair at £1,000–£2,500, and £206 or £462 for planning.

Assumptions Behind These Figures

Every figure here is restated from our loft conversion cost guide or calculator, including VAT at 20% on construction, materials and standard finishes, and excluding professional fees and planning fees. The published hip-to-gable band is £2,000–£2,800 per m², with a published 35 m² example of £70,000–£98,000, and London carries a published 30–50% premium. We publish no London total for this type and have not created one: the realistic budget is the combined scope priced at survey. Our guide advises adding 15–20% on top of a quoted build cost for fees and contingency.

Frequently Asked Questions

How much does a hip to gable loft conversion cost in London in 2026?

Our published rate is £2,000–£2,800 per m² including VAT, with a 35 m² example of £70,000–£98,000 nationally and a published 30–50% London premium. We publish no London total; our London bands are £39,000–£60,000 at 20 m², £58,500–£90,000 at 30 m² and £78,000–£120,000 at 40 m².

Does a hip to gable need planning permission?

Usually not on a house inside permitted development: nothing above the highest roof, no more than 40 m³ extra roof space on a terrace (50 m³ otherwise), similar materials, side windows obscure-glazed and non-opening below 1.7 m, no balcony. Conservation areas and flats fall outside it.

Which houses suit a hip to gable conversion?

Hipped roofs — in London usually 1930s semi-detached and inter-war detached houses. A mid-terrace house already has a gable end.

Can a hip to gable be done without a rear dormer?

It can be built, but is rarely enough alone: the hip adds volume at the end while central headroom stays governed by the pitch, so the stair and the usable floor area usually need the dormer too.

Is a hip to gable cheaper than a rear dormer?

No, on our published rates: £2,000–£2,800 per m² against £1,800–£2,500 for a dormer. The extra is structural. On a hipped roof the two are usually built as a pair.

Does a hip to gable need a party wall agreement?

Often, yes: on a semi the flank wall is frequently the party wall, so a party structure notice must be served at least two months before work begins. Our guide publishes £700–£2,000 for an agreement.

How long does a hip to gable conversion take?

Allow more than for a straight dormer: 6–10 weeks of construction and 4–8 weeks of design and planning for a dormer, plus the extra structural work and usually a party wall award.

Ready to Price Your Hip to Gable?

Feasibility comes first: whether the hip can come out, how the new gable meets the existing roof, and whether the volume allowance covers the room you want. A free survey and a structural view settle those three questions.

Book a free survey for your London loft conversion →

The loft conversion cost guide prices every conversion type; the dormer loft conversion guide covers the rear dormer this type is usually paired with; and the loft conversion cost calculator gives a London floor-area range.

Still comparing types? Our London loft conversion service.