Do I Need Planning Permission for a Rear Extension?

Most rear extensions in England do not need planning permission. Under permitted development rights, homeowners can extend the rear of their property without submitting a planning application — as long as the extension stays within specific size and height limits. Deeper extensions may still be possible via prior approval under the Larger Home Extension scheme, which is a lighter-touch process than full planning permission.

Under Class A of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, a single-storey rear extension is permitted development when all of the following are met:

• Extends no more than 3 metres from the original rear wall on a semi-detached or terraced house
• Extends no more than 4 metres from the original rear wall on a detached house
• Maximum height does not exceed 4 metres
• Eaves height does not exceed 3 metres if the extension is within 2 metres of a boundary
• Total area covered by additions does not exceed 50% of the original curtilage
• Materials are similar in appearance to the existing house
• Property is a house, not a flat or maisonette

Depths beyond these standard limits — up to 6 metres on semi-detached or terraced houses, and up to 8 metres on detached houses — are not standard permitted development. They require prior approval under the Larger Home Extension scheme.

The depth is measured from the original rear wall of the house as it existed on 1 July 1948 (or as built, if built after that date). If a previous extension was built after 1948, measurements are still taken from the original wall — not from the most recently added extension. This is a common source of confusion: you cannot stack extensions by measuring from a previous one.

If you are not sure where the original wall was, check historic maps or planning records held by your local authority. Satellite imagery on planning portals can sometimes help identify the original footprint.

• Extends no more than 3 metres from the original rear wall
• No closer than 7 metres to the rear boundary
• Roof pitch matches the existing house
• Any upper-floor window in a side elevation is obscure-glazed and non-opening below 1.7 metres from floor level
• No balcony, veranda or raised platform

The Larger Home Extension scheme does not cover two-storey extensions. If your two-storey rear extension exceeds 3 metres, you will need a full planning application.

Single-storey rear extensions between 3 and 6 metres (semi-detached or terraced) or between 4 and 8 metres (detached) are not automatic permitted development. They require prior approval under the Larger Home Extension neighbour consultation scheme:

• You notify the council before starting work
• Neighbours are formally consulted for 21 days
• The council fee is around £120 (varies by authority)
• If no objections are raised, the council should issue approval. If objections are raised, the council decides on design and amenity grounds only

The Larger Home Extension scheme does not apply on designated land, including conservation areas, National Parks, Areas of Outstanding Natural Beauty (National Landscapes), and World Heritage Sites. On designated land, anything beyond the standard 3 m / 4 m depths needs a full planning application.

• Property is a flat or maisonette
• Property is a listed building (also requires listed building consent)
• Extension exceeds the standard size limits and either exceeds the Larger Home Extension depths, or sits on designated land where that scheme is unavailable
• Article 4 direction removes permitted development rights locally
• Original planning permission conditions restrict extensions
• Extension would extend beyond the side wall of the house facing a highway

In conservation areas, permitted development rights for rear extensions still apply in most cases, but side extensions are not permitted development. The Larger Home Extension prior-approval route is also unavailable for extensions beyond the standard depths in a conservation area. Listed buildings always require listed building consent in addition to any planning permission, and effectively have no permitted development rights.

If your rear extension is within 3 to 6 metres of a neighbour's building, or if it involves excavation near a shared boundary, the Party Wall etc. Act 1996 may apply. You would need to serve a Party Wall notice on affected neighbours at least two months before starting work. This is entirely separate from planning permission and applies even when no planning permission is needed.

Planning permission and building regulations are completely separate processes. A rear extension almost always needs building regulations approval covering structural calculations, insulation (to meet Part L energy efficiency requirements), drainage, electrics, and fire safety — even when the work is permitted development or has prior approval under the Larger Home Extension scheme. Always apply to your local building control body or an approved inspector before starting structural work.

A single-storey rear extension typically costs between £20,000 and £50,000 in England, depending on size, specification, location, and finish. A full planning application, if required, costs £258 (as of 2024) plus architect fees. Prior approval under the Larger Home Extension scheme costs around £120. Building regulations fees are separate and depend on the value of the work. Extensions typically take 12–20 weeks to build once all approvals are in place.

Can I build a rear extension right up to my boundary? You can build up to the boundary in some cases, but if the extension is within 2 metres of a boundary, the eaves height is capped at 3 metres. Side walls close to boundaries may also trigger Party Wall Act requirements.

Does a previously built extension count towards my 3 m / 4 m limit? It depends when it was built. Pre-1948 extensions effectively set the new “original” rear wall position. Post-1948 extensions count as part of your permitted development allowance — you measure from the original 1948 wall, not from the more recent extension.

My neighbour objected during the Larger Home Extension consultation. Does that stop it? Not automatically. The council considers objections on design and amenity grounds only. A neighbour objecting on other grounds (noise, property value) does not give the council power to refuse prior approval. The council must decide within 42 days of receiving your application.