Planning Permission for Loft Conversions and Extensions

Planning permission for a loft conversion or extension is often not required as it can be designed and constructed under permitted development rules. Permitted development rights (PD) allow homeowners to improve and extend their homes without the need to apply for planning permission. Permitted Development is a general planning permission design granted to streamline basic planning applications. The great thing about it is you can carry out certain types of projects without needing to apply for planning permission.


Permitted Development for Loft Conversions

To carry out a loft conversion under permitted development certain rules for construction are applicable. The additional roof space created which protrudes outside of the existing roofline, must not exceed 40 cubic metres for terraced houses and 50 cubic metres for detached or semi-detached houses. Any previous roof space additions must be included within this volume allowance. A dormer constructed to the principal elevation, or front elevation, that faces a highway is not permitted development, so planning permission is required. Exterior materials used must be similar in appearance to the existing roof and house. No dormers or gable walls to be higher than the highest part of the existing roof (main ridge). Protruding balconies or raised platforms are not permitted development. Side facing windows must be obscure glass and non opening unless the opening window is 1.7 metres or more above the floor inside the room. When constructing a dormer for a loft conversion under permitted development, a measurement of at least 20cm from the bottom of the original eaves to the dormer must be remaining. The 20cm distance is measured along the roof slope. The dormer cannot protrude past the outer face of the wall of the original house.


Work on a loft or a roof may affect bats.

You need to consider protected species when planning a loft conversion. A loft survey may be needed, and if bats are present, a licence may be required.

Contact Natural England for more advice.

View specific information regarding Bats.

Permitted Development Rights are excluded for houses on designated land.

Planning Permission for Extensions

Single Storey Rear Extension

A single storey rear extension to a detached house cannot extend beyond the rear wall of the original house by more than 4 metres. For a semi-detached or terraced house it is no more than 3 metres.

If the house isn’t on designated land (Article 2(3)) or a Site of Special Scientific Interest and subject to ‘prior approval then for a detached house a single-storey rear extensions can be increased to 8 metres. For a semi-detached or terraced house it I can be extended to 6 metres.

Single-storey rear extensions cannot exceed four metres in height.

For Extensions More Than One Storey

Extensions that are more than one storey cannot extend beyond the rear wall of the original house by more than 3 metres or be within 7 metres of any boundary opposite the rear wall of the house.

The roof pitch must match the existing house as far as practicable. This also applies to an upper storey built on an existing extension.

An upper floor window located to the side elevation must be obscure glazed and non-opening unless the opener is more than 1.7 metres above the floor.

All side extensions of more than one storey requires planning permission.

On Article 2(3) designated land all rear extensions of more than one storey requires planning permission.

This is only a guide and should be treated as not being a definitive source of legal information. Our guidance is based on general national rules, additional local rules may affect the planning permissions required. Our guidance relates to the planning regime for England only.