Loft conversion planning permission and building regulations

Do I need planning permission for a loft conversion?

In England, many loft conversions on houses fall under permitted development. Typical conditions include staying within a volume allowance (40 cubic metres for terraced houses and 50 for detached and semi-detached), not extending beyond the existing roof plane on the front elevation, not going higher than the existing ridge, and using materials similar in appearance to the house.

Planning permission is more likely to be needed for a front dormer, a raised roof, a conservation area or listed building, a flat or maisonette, or where permitted development rights have been removed. A lawful development certificate gives written confirmation if you are unsure.

Dormer loft conversion planning permission

Rear dormers are often permitted development if they meet the conditions, including setbacks from the eaves. Side-facing windows usually need obscure glazing and to be fixed below a set height. Large or front-facing dormers, and hip to gable alterations on certain houses, are more likely to need an application.

Loft conversion building regulations

Building control checks the new floor structure, any steelwork, insulation, ventilation, sound insulation between floors, electrics and the staircase. Most conversions need new floor joists because ceiling joists are not designed to carry a room.

• Floor and roof structure
• Insulation and ventilation
• Fire safety and escape
• Stairs and headroom
• Sound insulation

Loft conversion fire regulations

Adding a loft room to a two-storey house usually creates a third storey, which changes the fire strategy. The typical approach is a protected stair enclosure from the loft down to an exit, with fire-resisting doors onto the stairs and mains-powered interlinked smoke alarms. Alternatives may be accepted in some layouts, and open-plan ground floors need particular thought.

Stairs and head height

The new stair needs adequate headroom, which for loft conversions can be slightly reduced at the stair compared with other stairs, along with suitable pitch, going and handrails. Finding space for the stair without losing a bedroom is often the deciding design question.

See our loft conversion stairs and head height guide for detail.

Party walls and approvals timing

On terraced and semi-detached houses, inserting steels into a shared wall usually triggers the Party Wall Act. Allow time for notices, planning or a lawful development certificate, and building regulations approval before work starts.

To plan your project, see our loft conversions service.

Before you commission drawings

Check whether your house has permitted development rights, whether it is in a conservation area and whether any previous extensions have used up part of the volume allowance. Measure the head height at the ridge, because there needs to be enough height once new floor joists and insulation are added. Note where the stair could land on the floor below. With that information, a designer can tell you early whether the scheme is likely to need an application, what the fire strategy will be and whether a dormer or roof alteration is needed. It is also worth checking with neighbours early if steels will go into a shared wall. Keeping the lawful development certificate or planning approval, building regulations completion certificate and party wall awards together will help when you come to sell.

Common questions