Permitted Development Extensions: Do You Need Planning? (UK 2026)

What is a permitted development extension?

Permitted development (PD) rights let you extend a house without applying for planning permission, because Parliament has already granted permission for work within set limits. Extensions fall under Class A of Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015, usually called the GPDO. Porches are Class D, roof extensions Class B and outbuildings Class E.

A permitted development extension must meet every limit and condition. Breaking just one, for example by going 10cm too high at the eaves, means the whole extension needs planning permission. That is why many homeowners get a lawful development certificate before building.

The “original house” rule

All depths and widths are measured from the original house: the house as first built, or as it stood on 1 July 1948 if it is older. Extensions added by previous owners count towards your allowance. GOV.UK’s technical guidance also says that a new extension joined to an existing one is assessed as one total enlargement, so you cannot build a 3m extension on the end of an earlier 3m extension and call both permitted development.

Permitted development rules 2026: summary of limits

Extension type	Maximum size without planning permission	Maximum height	Designated land (e.g. conservation area)
Single-storey rear, semi or terraced	3m beyond the original rear wall (6m with prior approval)	4m; eaves 3m if within 2m of a boundary	3m only; no prior approval route
Single-storey rear, detached	4m beyond the original rear wall (8m with prior approval)	4m; eaves 3m if within 2m of a boundary	4m only; no prior approval route
Two-storey (or more) rear	3m beyond the original rear wall and at least 7m from the rear boundary	No higher than the existing roof or eaves	Not permitted
Side extension	Single storey; width no more than half the original house	4m	Not permitted
Wrap-around (side and rear)	Must meet both the side and rear limits	4m, single storey	Not permitted
Porch	3m² ground area, measured externally; not within 2m of a boundary with a road	3m	Allowed
Conservatory	Treated as an extension: same limits as above	As above	As above
Outbuilding (e.g. garden room)	Single storey, not forward of the principal elevation	2.5m within 2m of a boundary; otherwise 4m dual-pitched roof, 3m other roofs	Restricted beside the house
All extensions and outbuildings together	No more than 50% of the land around the original house	–	Same

Rules that apply to every extension

Whatever the type, a Class A extension is not permitted development if:

• buildings (other than the original house) would cover more than 50% of the curtilage, the land around the original house, including sheds and outbuildings;
• it would be higher than the highest part of the existing roof, or its eaves higher than the existing eaves;
• it would extend beyond the principal elevation (normally the front) or a side elevation that fronts a highway;
• any part within 2m of a boundary has eaves higher than 3m;
• it includes a veranda, balcony or raised platform more than 30cm high, a chimney, flue or soil and vent pipe, a microwave antenna, or any alteration to the main roof.

Three conditions also apply: materials must be similar in appearance to the existing house (conservatories are exempt), upper-floor side windows must be obscure-glazed and non-opening unless the opening part is more than 1.7m above the floor, and a two-storey extension’s roof pitch should match the original house as far as practicable.

Rear extension permitted development: single storey

A single-storey rear extension can project up to 3m beyond the original rear wall on a semi-detached or terraced house, or 4m on a detached house, with a maximum height of 4m. Most kitchen and open-plan living extensions fall into this category, and a 3m-deep, full-width extension on a typical semi adds around 15–20m². Our rear extension cost guide and single-storey extension cost guide show what these sizes cost to build.

Watch the eaves. Many flat-roofed extensions sit right on the boundary, so any part within 2m of it must have eaves no higher than 3m. A side return infill on a terraced house is assessed under both the rear and side rules, as explained below.

6m extension prior approval: the larger home extension scheme

If you want to go deeper, the larger home extension scheme lets you build a single-storey rear extension up to 6m on a semi-detached or terraced house, or 8m on a detached house, still with a 4m height limit. You must apply to the council for prior approval before starting. The fee in England is £249 from 1 April 2026.

How the prior approval process works

1. Submit a written description of the extension (depth, height and eaves height), a plan of the site, the addresses of adjoining properties and your contact details, usually through the Planning Portal.
2. The council notifies adjoining neighbours, who have at least 21 days to comment.
3. If nobody objects, prior approval is not required. If a neighbour objects, the council assesses only the impact on the amenity of all adjoining properties, mainly light, outlook and privacy.
4. The council must decide within 42 days. If it gives no decision in that time, you can build the extension as described.
5. Build exactly to the details submitted or approved, including any conditions.

The scheme does not apply on designated land (conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites) or on a Site of Special Scientific Interest. The council can also refuse if the extension does not meet the other Class A limits, so the 50% coverage, eaves and materials rules still apply. A refusal can be appealed, or you can apply for full planning permission instead.

Two-storey rear extensions

An extension of more than one storey can be permitted development if it extends no more than 3m beyond the original rear wall and is at least 7m from the boundary opposite that rear wall. It must not be higher than the existing ridge or eaves, its roof pitch should match the house, and any upper-floor side windows must be obscure-glazed. The 7m rule rules out many terraced and semi-detached homes with short gardens. Two-storey rear extensions are not permitted development on designated land. See our two-storey extension cost guide for budgets.

Side extension permitted development

A side extension is permitted development only if it is single storey, no more than 4m high and no wider than half the width of the original house, measured at its widest point. It cannot extend beyond a side wall that faces a road. Two-storey side extensions always need planning permission, and on designated land no side extensions are permitted development at all. Our side extension cost guide covers prices, and our side return extension cost guide covers the narrow alley beside many Victorian terraces.

Wrap-around extensions

There is no separate category for wrap-around extensions. GOV.UK’s technical guidance says an extension that fills the area between a side wall and the rear wall must meet both sets of limits: single storey, no more than 4m high, no wider than half the original house, and no deeper than the rear limits (3m or 4m, or 6m or 8m with prior approval). In practice most wrap-arounds are wider than half the house once the side part is added, so the majority need a householder planning application. See our wrap-around extension cost guide.

Porches, conservatories and outbuildings

Porches

A porch outside any external door is permitted development if its ground area, measured externally, is no more than 3m², no part is more than 3m high and no part is within 2m of a boundary with a road or footpath. See our porch cost guide.

Conservatories

A conservatory is treated as an extension under Class A, so the same depth, height, width and 50% rules apply. The only concession is that its materials do not have to match the house. Many conservatories are also exempt from building regulations if they are under 30m², at ground level and separated from the house by external-quality doors, with no extension of the main heating. See our conservatory cost guide and lean-to conservatory cost guide.

Outbuildings and garden rooms

Detached outbuildings fall under Class E. They must be single storey with eaves no higher than 2.5m, no higher than 2.5m overall within 2m of a boundary (otherwise 4m with a dual-pitched roof or 3m for other roofs), must not be forward of the principal elevation, and must be used for purposes incidental to the house, not as a separate bedroom or self-contained home. They count towards the 50% coverage limit. See our garden room cost guide.

Conservation areas, Article 4 directions and designated land

On Article 2(3) land (conservation areas, National Parks, National Landscapes, formerly AONBs, the Broads and World Heritage Sites), the rules are tighter:

• no side extensions;
• no rear extensions of more than one storey;
• no cladding of the outside in stone, artificial stone, pebble dash, render, timber, plastic or tiles;
• no larger home extension prior approval route.

A single-storey rear extension within the standard 3m or 4m limits can still be permitted development in a conservation area. Separately, a council can remove PD rights altogether with an Article 4 direction, and many new-build estates have a planning condition removing them. Check your council’s website and your property’s planning history before relying on permitted development. Listed buildings need listed building consent for most works, even internal ones.

Flats and maisonettes

Householder permitted development rights apply only to houses. If you own a flat or maisonette, including a ground-floor flat in a converted house, any extension needs full planning permission, and usually the freeholder’s consent under your lease. Houses created through certain change-of-use permitted development rights, such as office-to-residential conversions, also do not benefit from Class A.

When do I need planning permission for an extension?

You need a householder planning application (£548 in England from 1 April 2026) if:

• the extension exceeds any of the limits above and is not covered by prior approval;
• it is at the front of the house or on a side facing a road;
• it is a two-storey side extension, or a two-storey rear extension closer than 7m to the rear boundary;
• you live in a flat or maisonette;
• PD rights have been removed by an Article 4 direction or planning condition;
• the property is on designated land and you want a side extension, a two-storey rear extension or external cladding.

Councils aim to decide householder applications within 8 weeks. They judge design, local policy and the impact on neighbours, who are formally notified. Many larger projects are approved, and a pre-application chat with the council or a designer can save a refused application. If refused, you can appeal within 12 weeks or amend and resubmit.

Route	Fee (England, from 1 April 2026)	Decision time	Neighbours consulted
Permitted development (no application)	£0	None needed	No
Lawful development certificate (proposed)	£274	8 weeks target	No statutory requirement
Prior approval, larger home extension	£249	42 days	Adjoining neighbours, 21 days
Householder planning application	£548	8 weeks target	Yes

Lawful development certificate: proof your extension is permitted

You can build genuine permitted development without telling the planning department. But because one wrong measurement can make the whole extension unlawful, we recommend a lawful development certificate (£274). It is the council’s formal confirmation that no planning permission is needed, and buyers’ solicitors often ask for it when you sell. Decisions usually take up to 8 weeks, so apply while your building regulations drawings are being prepared. Our lawful development certificate guide explains what to submit and what it costs with drawings. If you use the prior approval route, the council’s decision notice serves as your evidence for that extension.

Building regulations vs planning permission

Planning permission controls what an extension looks like and how it affects the area. Building regulations control how it is built: foundations, structure, fire safety, insulation, drainage, ventilation and glazing. Almost every extension needs building regulations approval, whether or not it needs planning permission. Fees are typically £600–£1,200 from your council or a registered building control approver, and you receive a completion certificate at the end. Small porches and some conservatories are exempt, as described above. Electrical work must be done by a registered electrician or approved by building control.

The Party Wall Act

Separate from both planning and building regulations, the Party Wall etc. Act 1996 applies if you build on or up to a boundary, cut into a shared wall, or dig foundations within 3m of a neighbour’s building (and lower than their foundations). You must serve notice at least one month before most excavation work and two months before work on a party wall. If a neighbour dissents, surveyor fees are typically £1,000–£3,000 per neighbour. See our party wall agreement guide and party wall surveyor cost guide.

Wales, Scotland and Northern Ireland

This guide covers England. Wales has its own permitted development rules: for example, its guidance allows single-storey rear extensions up to 4m and has a 10.5m boundary rule for two-storey extensions, and there is no equivalent of the 6m/8m prior approval scheme. Scotland and Northern Ireland run separate planning systems with different limits. Check with your local planning authority before you commit to a design.

Frequently asked questions

Can I build an extension without planning permission?

Yes, if it meets all the permitted development limits: for a house in England, typically a single-storey rear extension up to 3m deep (4m detached) and 4m high, or a single-storey side extension no wider than half the original house. Flats, listed buildings and homes with PD rights removed need planning permission.

How big can an extension be without planning permission?

Up to 3m deep on a semi or terrace and 4m on a detached house for a single storey, or 6m and 8m with prior approval. Height is capped at 4m, and all extensions and outbuildings together must cover no more than half the land around the original house.

Can I build a 6m extension without planning permission?

On a semi-detached or terraced house, only through prior approval (£249), which gives adjoining neighbours 21 days to comment and the council 42 days to decide. On a detached house, 6m is within the 8m prior approval limit. Neither applies on designated land.

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

Not always. A two-storey rear extension up to 3m deep that is at least 7m from the rear boundary can be permitted development. Two-storey side extensions always need planning permission.

Do I need planning permission for a wrap-around extension?

Usually yes. A wrap-around must meet both the side and rear limits, including the rule that it is no wider than half the original house, which most designs exceed.

Do previous extensions count towards permitted development?

Yes. Limits are measured from the original house as built, or as it stood on 1 July 1948, and a new extension joined to an existing one is assessed as one enlargement.

Have the permitted development rules changed in 2026?

The Class A extension limits in England have not changed in 2026, but planning fees rose from 1 April 2026: £548 for a householder application, £274 for a proposed LDC and £249 for larger home extension prior approval.

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