What is a hip-to-gable loft conversion?

A hip-to-gable conversion extends the sloping hip end of a roof outward to create a vertical gable wall, providing additional headroom and floor space in the loft. The hip rafters are removed, a new gable wall is built, and a structural ridge beam supports the extended roof. It is typically combined with a rear dormer.

Do I need planning permission for hip-to-gable?

On a detached house, hip-to-gable is usually Permitted Development provided the total volume addition stays within 50m³. On a semi-detached house, it is PD on the non-party wall side only (40m³ limit). The gable wall must not extend beyond the plane of the original house wall. Check with your local planning authority.

What steelwork is needed?

A structural ridge beam is the primary steel, spanning from the existing party wall (or internal support) to the new gable wall. This replaces the removed hip rafters and supports all the new and existing roof loads. A steel beam in the gable wall may also be needed. All steelwork must be designed by a structural engineer.

How many bricks are needed for the gable wall?

A standard brick gable wall needs approximately 60 bricks per m² (including mortar joints). The gable is typically triangular, so the area is (Width × Height) / 2. Matching existing bricks can be challenging — a combination of reclaimed and new bricks, or rendering/tile-hanging, may be more practical.

What about the tiles on the gable end?

When the hip is removed, the existing hip tiles are no longer needed. New tiles are required for any extended roof area. If tile-hanging the gable wall, allow approximately 10 tiles per m². Matching existing roof tiles may require sourcing from reclamation yards if the tiles are discontinued.

TradeCalculator.co.uk

Hip-to-Gable Calculator — Steelwork, Brickwork & Tiles

Calculate materials for a hip-to-gable loft conversion including gable wall brickwork, structural ridge beam, new rafters and tile quantities.

Gable Width

Width of the gable end wall

Gable Height (Ridge)

Height from eaves to ridge

Ridge Extension

How far the ridge extends (leave 0 for auto)

Gable Wall Finish

Number of Sides

1 for semi, 2 for detached

Price Per m² (optional)

Cost per m² of gable wall

How We Calculate This

This calculator estimates the materials needed for a hip-to-gable conversion based on the gable dimensions.

The formula

Gable Wall Area = (Width × Height) / 2

Bricks = Area × 60 bricks/m²

New Rafters = ceil(Ridge Extension / 0.4m spacing)

Key components

Structural ridge beam: Steel or glulam
Gable wall: Brick, block or timber frame
New rafters: To fill the extended roof area
Tiles: For extended and gable areas

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.