Two-storey extensions

A two-storey extension can be permitted development in England, but only at the rear of a house and only 3m deep. It must also be at least 7m from the boundary behind the house. Two-storey side and front extensions are never permitted development.

How it differs from single storey

	Single storey	Two storey
Rear depth, terrace or semi	3m (6m with prior approval)	3m
Rear depth, detached	4m (8m with prior approval)	3m
Distance to the rear boundary	No minimum	7m
To the side	Allowed, half the width	Not allowed
Conservation areas and other protected land	Allowed at the rear	Not allowed
Roof pitch	No rule	Match the house where practical

The prior approval route for deeper extensions is for single storey only.

The limits

• No more than 3m beyond the rear wall of the original house.
• At least 7m from the boundary opposite the rear wall.
• Eaves no higher than 3m within 2m of any boundary.
• No higher than the existing roof, and eaves no higher than the existing eaves.
• Upper-floor windows in a side wall obscure glazed, and fixed unless the opening part is more than 1.7m above the floor.
• No balconies, verandas or raised platforms.
• Where the roof joins the main roof, that work must also meet the roof rules for lofts and roof alterations.

Building on top of an existing extension

A first floor added over a single-storey extension counts as a two-storey extension. The old and new parts are measured together. So a ground-floor extension already more than 3m deep cannot take a first floor without permission.

Adding whole storeys on top of the house is a different right, and needs the council’s prior approval.

When permission is needed

• Deeper than 3m, or closer than 7m to the rear boundary.
• Any two-storey extension to the side or front.
• Flats and maisonettes.
• Conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites.
• Streets covered by an Article 4 direction that removes extension rights.

See also rear extensions and permitted development rights explained.

Source: The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2 Part 1, legislation.gov.uk; Permitted development rights for householders, technical guidance, Ministry of Housing, Communities and Local Government.