How Big Can I Build Without Planning Permission?

Permitted development (PD) rights allow homeowners in England to build certain extensions and alterations without submitting a planning application. The rules are set out in Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended) and they come with multiple conditions that all have to be satisfied simultaneously.¹ This guide explains the key limits in plain terms.

What Permitted Development Covers

PD rights for house extensions fall under Class A of Schedule 2, Part 1. The rules cover single-storey rear and side extensions and two-storey rear extensions. Roof alterations such as dormers fall under Classes B and C instead, not Class A.¹ Each category has its own dimensional constraints, and all must satisfy the general conditions:

• Extensions and outbuildings together (but not the original house) must not cover more than 50% of the curtilage, the land around the original house²
• The extension must not be forward of the principal elevation or side elevation fronting a highway²
• Materials must be of a similar appearance to the existing house²
• The property must be a house (not a flat or maisonette, and not a home created under the permitted development rights for changing a building’s use, such as from a shop or barn)¹
• PD rights can be removed by a condition on the planning permission for the house or by an Article 4 Direction: check the property’s planning history or ask the local planning authority¹

Single-Storey Rear Extensions: The Core Limits

Depth is measured from the original rear wall of the house, the wall as it was built or, for a house built before 1 July 1948, as it stood on that date.¹ Any previous rear extensions reduce what you can add. If a previous owner already extended 2 m into the garden, you have only 1 m of standard PD left (for a semi-detached), not 3 m.

Additional height constraints:

• Maximum eaves height: 3 m where the extension is within 2 m of any boundary²
• Maximum overall height: 4 m (ridge or flat roof top)
• The eaves of the extension must be no higher than the eaves of the existing house, and no part of it can be higher than the existing roof.² The 3 m eaves limit near a boundary often restricts a side-return infill or rear extension on a narrow plot

The Larger Home Extension Scheme (Prior Approval)

This scheme, made permanent in May 2019, allows single-storey rear extensions up to 8 m (detached) or 6 m (semi/terrace) deep without a full planning application.² However, it is not automatic, you must:

1. Notify the local authority before starting work
2. Include a written description (how far the extension projects beyond the rear wall, its maximum height and its eaves height), a plan of the site showing the proposed extension, and the addresses of any adjoining premises²
3. Pay the prior approval fee (£249 per application in England from 1 April 2026)³⁴
4. Wait 42 days for the local authority to consult neighbours and assess any objections²

If no adjoining owner or occupier objects, prior approval is not needed and you can proceed.² If someone objects, the authority must consider the amenity of all adjoining premises, not only those that objected; if it refuses prior approval you will need a full planning application or an appeal.²

The scheme does not change the height limits above, a 6 m deep extension still cannot exceed 4 m at the ridge or 3 m at the eaves within 2 m of the boundary.

Side Extensions

Single-storey side extensions are permitted under Class A with different constraints:

• Single storey only, no more than 4 m high and no wider than half the width of the original house²
• Must not extend forward of the principal elevation
• Must not be within 2 m of the boundary if over 3 m high at the eaves

There is no equivalent of the larger home extension scheme for side extensions, the half-width rule is absolute under PD. A full planning application is needed if you want to exceed it. Side extensions are not permitted development at all in a conservation area or on other article 2(3) land, and an Article 4 Direction covering extensions has the same effect.²

Two-Storey Rear Extensions

Two-storey rear extensions under PD are limited to:

• 3 m depth from the rear wall of the original house
• Must be no closer than 7 m to the rear boundary²
• Maximum roof height cannot exceed that of the existing house
• Any upper-floor windows in a side elevation must be obscure-glazed, and non-opening unless the opening parts are more than 1.7 m above the floor of the room²

The 7 m setback from the rear boundary eliminates two-storey PD rights for many terraced properties with short rear gardens.

Corner Plots and Wraparound Extensions

Corner plots face additional restrictions because they have two elevations that face a highway. On a corner plot:

• Side extensions cannot be built on the elevation that fronts a road under PD, they require full planning permission²
• A wraparound extension (extending both rear and side) must comply with the side constraints on the road-facing elevation and the depth/height constraints at the rear

In practice, many wraparound extensions on corner plots require a planning application, though the local authority may be supportive because there is no direct impact on a neighbour’s amenity.

Flats and Maisonettes

Permitted development rights under Schedule 2, Part 1 apply only to houses. Flats and maisonettes have no PD rights for extensions.¹ If you own a ground-floor flat with a garden, any extension, however small, requires a full planning application and very likely the consent of the freeholder and management company as well. Leasehold issues are entirely separate from planning law.

Conservation Areas, Listed Buildings, and Article 4 Directions

Listed buildings: Listing does not by itself remove the Class A extension rights, although outbuildings within the curtilage of a listed building always need planning permission.¹ You will, however, need listed building consent for any extension that affects the building’s character as a listed building, which in practice covers almost every extension.⁵ Historic England advises checking first with the local authority conservation officer whether consent will be needed.⁶

Conservation areas: Conservation areas are article 2(3) land, where side extensions, rear extensions of more than one storey, and cladding the outside of the house in stone, render, timber, plastic or tiles are not permitted development (Schedule 2, Part 1, Class A, paragraph A.2).² Rear single-storey extensions may still fall under PD, but only within the standard 3 m, or 4 m for a detached house, because the larger home extension scheme does not apply there.¹ Roof extensions such as dormers are not permitted development in a conservation area at all.⁷

Article 4 Directions: A local planning authority can withdraw specified PD rights across a defined area by making an Article 4 Direction.⁸ Compensation is payable only in limited cases, for example if the authority then refuses planning permission for work that would otherwise have been permitted development.⁸ Directions are often used in conservation areas to protect details such as doors and windows.⁵ Check with your local planning authority or search the council’s website for any Article 4 Directions affecting your street.

Checking Before You Build

The safest step before starting any extension is to apply for a Lawful Development Certificate (LDC) from the local planning authority. For proposed works the fee is half the normal planning application fee, so £274 for a householder proposal in England from 1 April 2026.⁴ The council must decide within 8 weeks unless you agree a longer period, and the certificate provides a legal record confirming that the proposed works are lawful under current PD rights.⁹ Without one, you rely on a self-assessment, adequate for most straightforward cases but problematic when selling the property if a solicitor raises questions. An LDC can be revoked only if a false statement was made or information was withheld to obtain it, and it stays with the property.¹⁰

Many planning consultants offer a fixed-fee PD assessment, often a few hundred pounds, useful on awkward plots or where the dwelling has had previous extensions that eat into the permitted envelope.