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Larger home extension: the 6 m and 8 m rules
A larger home extension can allow a deeper single-storey rear extension under Class A in England: up to 8 m for a detached house or 6 m for any other house. You must follow the council notification and prior approval procedure before starting.
This is not permission to build any extension inside an 8 m or 6 m box. All the other Class A rules still apply, including the side-width rule where an outrigger or wraparound design is involved.
Need help with permitted development?
Permitted development can avoid a full planning application, but only if the right applies and every relevant limit and condition is met. Planning Geek can check the planning history, Article 4 directions and other restrictions, and help with a lawful development certificate or prior approval where needed.
Which rear extension needs this procedure?
Swipe to view the full table
| House | Ordinary single-storey rear limit | Larger home extension range |
|---|---|---|
| Detached | Up to 4 m | More than 4 m, up to and including 8 m |
| Any other house | Up to 3 m | More than 3 m, up to and including 6 m |
Measure from the relevant original rear wall. A later extension does not give you another 6 m or 8 m starting from its back wall. An original stepped rear can have more than one relevant rear wall.
The extension must be single-storey and no more than 4 m high. Where any part is within 2 m of a curtilage boundary, its eaves must not exceed 3 m. The existing house’s roof and eaves limits also apply.
Where the larger allowance is unavailable
A.1(g) excludes houses on article 2(3) land or a Site of Special Scientific Interest. That includes conservation areas, National Parks, the Broads, National Landscapes and World Heritage Sites for the article 2(3) restriction.
The proposal must also qualify for Class A itself. Flats and maisonettes do not qualify. Class A excludes houses whose residential permission arose only through Part 3 Classes G, M, MA, N, P, PA or Q, and houses built under Part 20. Check the planning history, any conditions restricting rights and any relevant Article 4 direction.
A larger rear allowance does not permit a wider wraparound
If the enlargement projects beyond an original side wall, including the side of an original outrigger, its width must not exceed half the width of the original house. The side-width allowance stays the same even when the larger rear-depth allowance is available.
In the drawing, an 8 m wide original house has a 4 m half-width allowance. The whole connected enlargement is 8 m wide, so it fails that side test. A 6 m rear projection does not cure the problem.
Where proposed work joins an existing enlargement, A.1(ja) requires the relevant measurements to be assessed for the total enlargement. The submission must describe and show that joined work too. See our side extension guide and rear extension guide.
What must you send to the council?
Before beginning development, A.4(2) requires:
- A written description giving the rear projection, maximum height and eaves height
- Those measurements for the total enlargement where the proposal will join an existing enlargement
- A plan identifying the site and showing the proposal and any existing enlargement it will join
- The addresses of adjoining premises
- Your contact address and an email address if you agree to electronic communication
- The required application fee
Clear existing and proposed plans and elevations help the council establish that all the Class A rules are met. It may refuse where the development does not comply or the information is insufficient to establish compliance. It can also ask for further information reasonably required to determine the application. See the planning application fees guide for the current fee.
How neighbour consultation works
The council must notify each adjoining owner or occupier, describing the proposal and the relevant receipt and deadline dates. It must send you a copy of the notice. The period for representations must be at least 21 days from the notice; public holidays are disregarded when calculating that consultation period.
Adjoining premises can be at the sides or rear, and are not limited to residential properties. If an adjoining owner or occupier objects, prior approval is required for the impact on the amenity of adjoining premises. The council must consider the amenity of all adjoining premises, not just those whose owners or occupiers objected.
An objection is not an automatic veto. Equally, no objection does not excuse a breach of Class A. The council can refuse a non-compliant or insufficiently evidenced proposal under A.4(3) without carrying out the usual consultation steps specified in A.4(4).
When can you start work?
Under A.4(10), you must wait until one of these happens:
- You receive the council’s written notice that prior approval is not required
- You receive its written notice granting prior approval
- The statutory 42-day period expires without the council notifying you whether prior approval is given or refused
The 42-day period runs from receipt of the information required by A.4(2). Keep evidence of the submission, receipt and fee. Do not assume that an incomplete notification, a wrong measurement or an ineligible proposal becomes lawful just because 42 days pass.
The public-holiday exception in A.4(16) concerns the minimum neighbour representation period. It does not turn the 42-day period into 42 working days.
Do not begin early. The procedure is a pre-commencement condition; applying afterwards is not a reliable route to regularising work already started.
What must happen after the decision?
If prior approval is required, build in accordance with the approved details. If it is not required, or the 42-day provision applies, build in accordance with the information submitted. A.4(11) allows a different arrangement where the council and developer agree otherwise in writing. Prior approval may also carry conditions reasonably related to adjoining amenity.
A refusal of prior approval, including a refusal under A.4(3), can be appealed. A revised compliant scheme or an ordinary householder planning application may be a better route, depending on why it failed.
Does the 45-degree rule decide the application?
A council’s 45-degree rule is not a national dimensional requirement of Class A. Where an adjoining objection triggers the amenity assessment, the council considers the actual impact on adjoining premises. Local amenity guidance can be relevant, but it should not be confused with the statutory permitted development limits or treated as a neighbour vote.
Other requirements still matter
Check the full Class A guide for ground coverage, materials, principal elevations, highways and excluded balconies or raised platforms. Building Regulations, listed building consent, party wall matters and property rights are separate from prior approval. Check any CIL extension procedure before work starts.
The larger-extension right is not subject to the old temporary completion deadline. Removed provisions in older versions of A.4 should not be carried forward as current requirements.
Sources and Class A legislation
Current GPDO Part 1 and article 2 definitions provide the statutory wording. The government householder technical guidance explains measurements and examples, but must be read alongside later legislative amendments.
Read the Class A legislation
Class A – enlargement, improvement or other alteration of a dwellinghouse
Permitted Development
A. The enlargement, improvement or other alteration of a dwellinghouse.
Development not permitted
A.1 Development is not permitted by Class A if—
(a)permission to use the dwellinghouse as a dwellinghouse has been granted only by virtue of Class G, M, MA, N, P , PA or Q of Part 3 of this Schedule (changes of use);
(b)as a result of the works, the total area of ground covered by buildings within the curtilage of the dwellinghouse (other than the original dwellinghouse) would exceed 50% of the total area of the curtilage (excluding the ground area of the original dwellinghouse);
(c)the height of the part of the dwellinghouse enlarged, improved or altered would exceed the height of the highest part of the roof of the existing dwellinghouse;
(d)the height of the eaves of the part of the dwellinghouse enlarged, improved or altered would exceed the height of the eaves of the existing dwellinghouse;
(e)the enlarged part of the dwellinghouse would extend beyond a wall which—
(i)forms the principal elevation of the original dwellinghouse; or
(ii)fronts a highway and forms a side elevation of the original dwellinghouse;
(f)subject to paragraph (g), the enlarged part of the dwellinghouse would have a single storey and—
(i)extend beyond the rear wall of the original dwellinghouse by more than 4 metres in the case of a detached dwellinghouse, or 3 metres in the case of any other dwellinghouse, or
(ii)exceed 4 metres in height;
(g)for a dwellinghouse not on article 2(3) land nor on a site of special scientific interest, the enlarged part of the dwellinghouse would have a single storey and—
(i)extend beyond the rear wall of the original dwellinghouse by more than 8 metres in the case of a detached dwellinghouse, or 6 metres in the case of any other dwellinghouse, or
(ii)exceed 4 metres in height;
(h)the enlarged part of the dwellinghouse would have more than a single storey and—
(i)extend beyond the rear wall of the original dwellinghouse by more than 3 metres, or
(ii)be within 7 metres of any boundary of the curtilage of the dwellinghouse being enlarged which is opposite the rear wall of that dwellinghouse;
(i)the enlarged part of the dwellinghouse would be within 2 metres of the boundary of the curtilage of the dwellinghouse, and the height of the eaves of the enlarged part would exceed 3 metres;
(j)the enlarged part of the dwellinghouse would extend beyond a wall forming a side elevation of the original dwellinghouse, and would—
(i)exceed 4 metres in height,
(ii)have more than a single storey, or
(iii)have a width greater than half the width of the original dwellinghouse;
(ja)any total enlargement (being the enlarged part together with any existing enlargement of the original dwellinghouse to which it will be joined) exceeds or would exceed the limits set out in sub-paragraphs (e) to (j);
(k)it would consist of or include—
(i)the construction or provision of a verandah, balcony or raised platform,
(ii)the installation, alteration or replacement of a microwave antenna,
(iii)the installation, alteration or replacement of a chimney, flue or soil and vent pipe, or
(iv)an alteration to any part of the roof of the dwellinghouse ; or
(l)the dwellinghouse is built under Part 20 of this Schedule (construction of new dwellinghouses).
A.2 In the case of a dwellinghouse on article 2(3) land, development is not permitted by Class A if—
(a)it would consist of or include the cladding of any part of the exterior of the dwellinghouse with stone, artificial stone, pebble dash, render, timber, plastic or tiles;
(b)the enlarged part of the dwellinghouse would extend beyond a wall forming a side elevation of the original dwellinghouse; or
(c)the enlarged part of the dwellinghouse would have more than a single storey and extend beyond the rear wall of the original dwellinghouse;
(d)any total enlargement (being the enlarged part together with any existing enlargement of the original dwellinghouse to which it will be joined) exceeds or would exceed the limits set out in sub-paragraphs (b) and (c).
Conditions
A.3 Development is permitted by Class A subject to the following conditions—
(a)the materials used in any exterior work (other than materials used in the construction of a conservatory) must be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse;
(b)any upper-floor window located in a wall or roof slope forming a side elevation of the dwellinghouse must be—
(i)obscure-glazed, and
(ii)non-opening unless the parts of the window which can be opened are more than 1.7 metres above the floor of the room in which the window is installed; and
(c)where the enlarged part of the dwellinghouse has more than a single storey, or forms an upper storey on an existing enlargement of the original dwellinghouse, the roof pitch of the enlarged part must, so far as practicable, be the same as the roof pitch of the original dwellinghouse.
A.4—(1) The following conditions apply to development permitted by Class A which exceeds the limits in paragraph A.1(f) but is allowed by paragraph A.1(g).
(2) Before beginning the development the developer must provide the following information to the local planning authority—
(a)a written description of the proposed development including—
(i)how far the enlarged part of the dwellinghouse extends beyond the rear wall of the original dwellinghouse;
(ii)the maximum height of the enlarged part of the dwellinghouse; and
(iii)the height of the eaves of the enlarged part of the dwellinghouse;
(iv)where the enlarged part will be joined to an existing enlargement of the dwellinghouse, the information in sub-paragraphs (i) to (iii) must be provided in respect of the total enlargement (being the enlarged part together with the existing enlargement to which it will be joined);
(b)a plan indicating the site and showing the proposed development and any existing enlargement of the original dwellinghouse to which the enlarged part will be joined;
(c)the addresses of any adjoining premises;
(d)the developer's contact address; and
(e)the developer's email address if the developer is content to receive communications electronically,
together with any fee required to be paid.
(3) The local planning authority may refuse an application where, in the opinion of the authority—
(a)the proposed development does not comply with, or
(b)the developer has provided insufficient information to enable the authority to establish whether the proposed development complies with,
the conditions, limitations or restrictions applicable to development permitted by Class A which exceeds the limits in paragraph A.1(f) but is allowed by paragraph A.1(g).
(4) Sub-paragraphs (5) to (7) and (9) do not apply where a local planning authority refuses an application under sub-paragraph (3) and for the purposes of section 78 (appeals) of the Act such a refusal is to be treated as a refusal of an application for approval.
(5) The local planning authority must notify each adjoining owner or occupier about the proposed development by serving on them a notice which—
(a)describes the development by setting out the information provided to the authority by the developer under paragraph A.4(2)(a);
(b)provides the address of the proposed development;
(c)specifies the date when the information referred to in sub-paragraph (2) was received by the local planning authority and the date when the period referred to in sub-paragraph (10)(c) would expire; and
(d)specifies the date (being not less than 21 days from the date of the notice) by which representations are to be received by the local planning authority.
(6) The local planning authority must send a copy of the notice referred to in sub-paragraph (5) to the developer.
(7) Where any owner or occupier of any adjoining premises objects to the proposed development, the prior approval of the local planning authority is required as to the impact of the proposed development on the amenity of any adjoining premises.
(8) The local planning authority may require the developer to submit such further information regarding the proposed development as the authority may reasonably require in order to determine the application.
(9) The local planning authority must, when considering the impact referred to in sub-paragraph (7)—
(a)take into account any representations made as a result of the notice given under sub-paragraph (5); and
(b)consider the amenity of all adjoining premises, not just adjoining premises which are the subject of representations.
(10) The development must not begin before the occurrence of one of the following—
(a)the receipt by the developer from the local planning authority of a written notice that their prior approval is not required;
(b)the receipt by the developer from the local planning authority of a written notice giving their prior approval; or
(c)the expiry of 42 days following the date on which the information referred to in sub-paragraph (2) was received by the local planning authority without the local planning authority notifying the developer as to whether prior approval is given or refused.
(11) The development must be carried out—
(a)where prior approval is required, in accordance with the details approved by the local planning authority;
(b)where prior approval is not required, or where sub-paragraph (10)(c) applies, in accordance with the information provided under sub-paragraph (2),
unless the local planning authority and the developer agree otherwise in writing.
(12) The local planning authority may grant prior approval unconditionally or subject to conditions reasonably related to the impact of the proposed development on the amenity of any adjoining premises.
(16) When computing the number of days in sub-paragraph (5)(d), any day which is a public holiday must be disregarded.
Explore GPDO Part 1
Choose the work you are planning. These guides explain the English rules for houses.
- Part 1 overview
Start here for permitted development at a house - Class A: house extension and alteration
Rear and side extensions, windows and doors - Class AA: additional storeys
Build upwards above an existing house - Class B: roof enlargement
Dormers and hip-to-gable enlargements - Class C: other roof alteration
Rooflights and other roof alterations - Class D: porch
Porches outside an external door - Class E: outbuilding
Garden buildings, pools and other incidental development - Class F: hard surface
Driveways, paths and patios - Class G: chimney and flue
Chimneys, flues and soil and vent pipes - Class H: satellite dish
Microwave antennas on the house or in its curtilage - Paragraph I: definitions
Terms used in Part 1
Page Updated: 25th September 2026