Do you need planning permission for an extension?

What is permitted development?

Permitted development rights allow householders to extend their homes without applying for planning permission, provided the work meets specific limits and conditions. They apply to houses only. They do not apply to flats and maisonettes, to houses converted or created under certain other permitted development rights, or where a planning condition or an Article 4 direction has limited or removed them.

Two terms matter throughout. The “original house” means the house as it was first built, or as it stood on 1 July 1948 if it is older, so a previous owner’s extension still counts. And the limits apply to the total enlargement: the new extension plus any earlier ones. These rules are for England; the Planning Portal notes that the policy in Wales may differ.

Which limits apply to every extension?

Under the Planning Portal’s summary of the rules, for any extension:

• no more than half the area of land around the original house can be covered by extensions or other buildings
• it cannot be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves
• within 2 metres of a boundary, the eaves cannot be more than 3 metres high
• it cannot be built forward of the principal elevation, or of a side elevation that fronts a highway
• it cannot include verandas, balconies or raised platforms, a chimney, flue or soil and vent pipe, a microwave antenna, or any alteration to the roof of the existing house
• the materials must look similar to those on the outside of the existing house
• on designated land, the work cannot include cladding the outside

How far can a single-storey rear extension go?

Without any application, a single-storey rear extension can go up to 3 metres beyond the rear wall of the original house, or 4 metres for a detached house, and no more than 4 metres high. The measurement runs from the base of the original rear wall to the outer face of the new wall, not counting guttering.

Outside designated land and Sites of Special Scientific Interest, the limit rises to 6 metres, or 8 metres for a detached house, through the prior approval process described below. The height limit stays at 4 metres.

What is prior approval for a larger rear extension?

Prior approval applies only to larger single-storey rear extensions: over 3 and up to 6 metres for most houses, or over 4 and up to 8 metres for a detached house. You apply to the local authority, which tells the adjoining neighbours about the plans. If a neighbour objects, the council decides whether the effect on neighbouring homes is acceptable.

The technical guidance says work cannot start until the council confirms that prior approval is not needed, or gives it, or 42 days pass without a decision. The Planning Portal calls this route the larger home extension.

Do you need planning permission for a side extension?

A side extension can be permitted development if it is single-storey, no more than 4 metres high and no more than half the width of the original house, measured at its widest point. On designated land, every side extension needs householder planning permission.

Where a side extension also wraps around the back, both sets of limits apply at once, which is why a full wrap-around usually needs an application. The wrap-around extension guide explains how.

Can you build a two-storey extension without planning permission?

Only at the back, and only within these limits from the Planning Portal:

• no more than 3 metres beyond the rear wall of the original house
• not within 7 metres of any boundary opposite the rear wall
• the roof pitch must match the existing house as far as practicable
• any upper-floor window in a side wall must be obscure-glazed and non-opening, unless the opening part is more than 1.7 metres above the floor
• every side extension of more than one storey needs householder planning permission
• on designated land, every rear extension of more than one storey needs householder planning permission

When do you need a planning application?

If an extension goes beyond any of these limits, the Planning Portal says it is likely to need a householder planning application. That also covers the cases above where permitted development does not apply. Designated land means a conservation area, an Area of Outstanding Natural Beauty, a National Park, the Broads, a World Heritage Site, or land specified for protecting the natural beauty of the countryside.

Citizens Advice adds that a listed building may need listed building consent as well. And if an extension adds over 100 square metres of floor space, the Planning Portal notes it may be liable for the Community Infrastructure Levy. If in doubt, check with your council before work starts.

Is planning the only approval you need?

No. Building regulations approval is separate from planning permission, and gov.uk says you might need both. The Planning Portal says most extensions need building regulations approval. Work near a neighbour’s house or on the boundary may need notices under the Party Wall Act. Citizens Advice also suggests checking your title deeds for covenants, your lease if the home is leasehold, and your mortgage conditions.

What extensions does Brick2Brick UK build?

Since 2023 the team has built single-storey extensions, a kitchen extension on a bungalow, a garage extension, a rear double-storey extension and two wrap-arounds in 2025. Whichever route an extension takes through planning, the build stages are the same: footings, damp proof course, floor slab, walls, steels, roof and windows. See extensions for the jobs.

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