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Can I build an extension without planning permission?

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UKUpdated 6 October 2026 · Written by BuyMeWhiskey Editorial Team · How we check facts

Often yes in England: a single-storey rear extension of up to 3 metres on a semi or terrace (4 metres detached) and up to 4 metres high is usually permitted development, but break any one limit on depth, side width, height, boundaries or the 50% garden rule and you need planning permission.

Check your design against every limit in the government's technical guidance, then ask your council for a Lawful Development Certificate before you build.

Read the GOV.UK technical guidance

Permitted development: building without a planning application

In England, houses have permitted development rights that allow many extensions without applying for planning permission, as long as every limit and condition is met. If a design breaks even one rule, the whole extension needs a planning application. It doesn't mean the answer is no; it means the council decides.

These rights apply to houses only, not flats or maisonettes. The council can remove them with an Article 4 Direction, or they may have been removed by a condition on an earlier planning permission, and they're tighter in conservation areas, National Parks, areas of outstanding natural beauty and World Heritage Sites (called "Article 2(3) land").

Single-storey rear extensions

Up to 4 metres beyond the original rear wall for a detached house, or 3 metres for any other house (semi, terrace), and no more than 4 metres high.
Larger extensions: outside Article 2(3) land and sites of special scientific interest, you can go up to 8 metres (detached) or 6 metres (other houses) using the prior approval scheme. You notify the council, which consults the neighbours, and you can't start until the council says prior approval isn't needed, gives it, or 42 days pass without a decision.
If any part is within 2 metres of a boundary, the eaves can't be higher than 3 metres.
Eaves can't be higher than those of the existing house.

Two-storey rear extensions

An extension of more than one storey can't extend more than 3 metres beyond the original rear wall, and must be at least 7 metres from the boundary opposite the rear wall. It isn't permitted development at all on Article 2(3) land. As with any extension under these rules, exterior materials must be similar in appearance to the existing house (conservatories excepted).

Side extensions

An extension beyond a side wall must be single storey, no more than 4 metres high, and no wider than half the width of the original house, measured at its widest point. A wraparound extension, filling the corner between the side and back, has to meet both the rear and the side rules at once. Side extensions aren't permitted development on Article 2(3) land.

Front extensions and the 50% rule

Nothing under permitted development can extend beyond the principal elevation, which is usually the front facing the main road, or beyond a side wall that faces a road on a corner plot. Separately, all extensions and outbuildings together, other than the original house, mustn't cover more than 50% of the land around the original house.

"Original house" and earlier extensions

Limits are measured from the original house: as it was built or as it stood on 1 July 1948 if older. Earlier extensions count. If a previous owner added a 3-metre conservatory to a semi, a new extension joined to it is measured as one total enlargement.

Get certainty before you build

Ask the council for a Lawful Development Certificate. It isn't compulsory, but it confirms your design is permitted development, which helps if neighbours object or when you sell.
If you do need permission, a householder application in England for one house costs £548 from 1 April 2026. Most applications are decided within 8 weeks, and you can appeal a refusal.
Building without permission you needed risks an enforcement notice ordering you to undo the work.

Other rules that still apply

Permitted development only answers the planning question. You still need building regulations approval for most extensions, and if you work on or near a shared wall you must serve a party wall notice: between 2 months and a year before starting work on a party wall. Your neighbour has 14 days to consent in writing, and silence doesn't count as agreement.

Wales, Scotland and Northern Ireland have their own rules, so check with your local planning authority there.

Maximum single-storey rear extension depth (metres, England)

Worked example

Priya owns a semi-detached house that is 7 metres wide, with a rear and side garden of 150 m² (not counting the house) and an existing 10 m² shed. She plans a wraparound extension: 5 metres deep at the back and 4 metres wide at the side.

Side width: the limit is half the original width: 7 ÷ 2 = 3.5 metres. Her 4-metre side section breaks the rule, so as drawn the whole scheme needs planning permission.
Rear depth: 5 metres is more than the standard 3 metres for a semi, but within the 6-metre limit under prior approval, if she isn't on Article 2(3) land.
The 50% rule: she may cover up to 150 × 50% = 75 m². A rear section of 5 × 7 = 35 m² plus the shed's 10 m² is 45 m², leaving room for the side section too.

Her options: narrow the side section to 3.5 metres or less and apply for prior approval for the 5-metre rear depth, or keep the design and apply for householder planning permission at £548. Either way, she'll need building regulations approval and party wall notices to her attached neighbour.

Am I right in thinking I can't build my extension the way I've planned?#

If your design breaks any permitted development limit, such as being too deep, too wide at the side, too tall near a boundary or in front of the main elevation, it can't go ahead without a planning application. That doesn't mean it will be refused. Check each rule in the government's technical guidance, then either adjust the design or apply.

How far can I extend without planning permission?#

A single-storey rear extension can go 3 metres beyond the original rear wall of a semi or terrace, or 4 metres for a detached house. Using prior approval, that rises to 6 metres or 8 metres outside protected areas. Height is capped at 4 metres.

Can I build a side extension under permitted development?#

Yes, if it's single storey, no more than 4 metres high and no wider than half the width of the original house. It isn't allowed on Article 2(3) land, such as a conservation area. A wraparound extension must meet both the side and rear limits.

Do I need planning permission for a two-storey extension?#

Not always. Outside protected Article 2(3) areas, a two-storey rear extension can be permitted development if it goes no more than 3 metres beyond the original rear wall and stays at least 7 metres from the rear boundary. Two-storey side or front extensions need planning permission.

What is a larger home extension (prior approval)?#

It lets a single-storey rear extension go up to 6 metres on a semi or terrace, or 8 metres on a detached house, outside protected areas. You notify the council, it consults the neighbours, and you can start once it says yes, says approval isn't needed, or 42 days pass without a decision.

How much does a planning application for an extension cost?#

In England, a householder application for one house costs £548 from 1 April 2026. Most decisions are made within 8 weeks. If you're refused, you can change the plans and reapply, or appeal.

Do permitted development rights apply to flats?#

No. Householder permitted development rights cover houses only, not flats or maisonettes. Any extension to a flat needs a planning application.

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Sources

Figures checked against these sources on 6 October 2026. If a rule changes, we update the page and its date.

General information, not personal financial advice. Rules depend on your circumstances; check the official source or speak to a regulated adviser before acting.