Extensions

Side Return Extension London: Planning and Building Rules

When a London side return or wraparound extension is permitted development, when it needs a householder application, and what building regs and party walls add.

FixedFeePlans editorial team
The back of a brick house with a single-storey rear extension under construction, a steel beam spanning the new opening and blockwork walls either side
A rear extension under construction: the steel beam over the new opening is the structural detail building control checks. Photo by Brett Jordan on Pexels.

A side return extension in London needs planning permission in a conservation area, because permitted development bars every side extension there. Elsewhere it can be permitted development if it is one storey, no higher than 4m and no wider than half the original house. Otherwise a householder application costs £548.

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The side return is the strip of garden beside the back outrigger of a typical London terrace. A side return extension fills it. A wraparound extension fills it and also extends across the back. Either is a popular way to get a bigger kitchen. The rules look simple until you combine the two extensions. This post takes them in the order a planning officer would.

When is a side return extension permitted development?

A side return can be permitted development when it meets the Class A limits. These come from Part 1 of Schedule 2 to the 2015 General Permitted Development Order. The Planning Portal summarises the ones that matter for a side extension (Planning Portal, extensions).

Limit Rule for a side extension
Storeys One only
Height No more than 4m
Width No more than half the width of the original house
Eaves within 2m of a boundary No higher than 3m
Position Not in front of the principal elevation, or the side wall facing a road
Materials A similar appearance to the existing house
Not allowed A balcony, a raised platform, or a change to the existing roof

Here is a worked example. If the original house is 6m wide at its widest point, a side extension can be up to 3m wide.

The 3m eaves limit matters because a side return sits against the boundary. The "original house" means the house as first built, or as it stood on 1 July 1948. An earlier owner's extension counts against you.

These rights are for houses. They do not cover flats or maisonettes, or houses that were converted or created under other permitted development rights. In a conservation area every side extension needs a householder application. An Article 4 direction can remove rights too. Check both before you pay for drawings. Our permitted development checker gives a straight answer, including "you do not need us".

What changes when the extension wraps around the back?

A wraparound extension must meet the rear limits and the side limits together. GOV.UK's technical guidance says so where an extension fills the area between a side wall and a rear wall (GOV.UK, householder permitted development: technical guidance).

So it must be one storey, no higher than 4m and no wider than half the house. It must also stay within the permitted depth beyond the rear wall. That depth is 3m for a terraced house, or up to 6m through the prior approval route (Planning Portal, prior approval).

The guidance gives a worked example of a failure. An extension is under half the house's width and reaches only 3m beyond one rear wall. It reaches further than the permitted depth beyond another. It is not permitted development, and it needs a planning application.

Two traps catch owners who build in stages:

  • Earlier work counts. Where a new extension joins an earlier one, the guidance tests the total enlargement, not just the new part.
  • The total width is tested. A side extension that was fine on its own can fail once a rear extension joins it and pushes the total width past half the house.

Going beyond 3m at the back is a separate process. Our guide to larger home extension prior approval covers the notice, the neighbour consultation and the fee.

How do two London boroughs judge side extensions?

Councils judge side returns on harm to a neighbour's light and outlook, and on the look of the street. The national limits decide whether you need to ask. A council deciding an application then uses its own design guidance, and that varies by borough. Two examples show the kind of test.

Hounslow's residential extension guidelines (May 2024 edition) warn that an extension running the full depth of an outrigger can block daylight and sunlight to the neighbour. Where an infill goes beyond the depth the guidelines allow, they ask for eaves on the shared boundary of no more than 2m and a roof pitch of no more than 45 degrees, sloping away from the boundary (Hounslow Council, A5 residential extension guidelines).

Haringey says it will consider a larger extension if it is smaller than the original building, avoids blocking sunlight to neighbours and keeps its windows from looking into their habitable rooms. It also asks that the extension does not shrink the garden unreasonably (Haringey Council, rear extensions).

These are two boroughs' rules, not London-wide ones. Read your own council's guidance before you design to a depth. If the scheme is near a limit, ask for pre-application advice. Our request service costs £295, credited against the planning service if you go ahead.

What else does a side return need besides planning?

Most extensions need building regulations approval, whether or not they need planning permission. The Planning Portal says so, and lists a few exempt classes (Planning Portal, building regulations for extensions). A side return often has a new steel beam where the old back wall comes out. Expect structural calculations as well as drawings.

Three other items belong on the checklist:

  • Party wall. GOV.UK's explanatory booklet says you must serve a notice if you build a wall on your own land but up against the boundary line. It must be served at least one month before work starts. Works to an existing party wall need two months. Excavating foundations near a neighbour's building can need a notice too (GOV.UK, party wall explanatory booklet). A side return usually touches the boundary, so ask a party wall surveyor which sections apply. Our Party Wall Act notices guide explains the periods.
  • Community Infrastructure Levy. The Planning Portal says work adding over 100 square metres of floor space may be liable. Ask your council whether the levy applies to your whole project.
  • Energy rules. The new building must meet Part L, which our Part L guide in the related reading below explains.

What do the drawings cost?

The planning side has two published costs. Our complete planning drawing service is £895. The council's householder fee is £548, paid to the council when you submit. GOV.UK lists that figure for extending a single dwellinghouse (GOV.UK (MHCLG), fees from 1 April 2026).

If your scheme is permitted development and you want proof for a buyer or lender, a certificate of lawfulness is from £950. Its council fee is £274. Building regulations drawings are £795, and structural calculations are from £495. The house extensions page sets these out stage by stage.

Do you need an architect, or just drawings?

Fixed fee drawings suit a scheme that is already decided: a known footprint, a standard route and a builder waiting for a drawing set. An architect suits a scheme where the design is still open, the site is sensitive, or you want someone to manage the project to completion.

You are more likely to want an architect if the house is in a conservation area and the design must win the council over. The same goes if the side return is one part of a bigger remodel, or if the brief is unclear. In that case a local architect can take you from brief to planning drawings. Once drawings and permissions are in place, local builders can price the work from a full set. That is the best way to compare quotes like for like.

Disclosure: the two sister-site links above go to sites in The MyLocal Network, which FixedFeePlans is part of.

Frequently asked questions

Can I fill my side return without planning permission? Sometimes. It must meet the Class A limits above, and the house must not be in a conservation area or under an Article 4 direction that removes the right.

Does a wraparound extension count as one extension? Yes. It is tested as one enlargement against both the rear and side limits, together with any earlier extension it joins.

Do I need a party wall notice for a side return? Often. GOV.UK's booklet says a new wall built up to the boundary needs a notice, and so do works to a shared wall. A party wall surveyor can tell you which sections apply to your plans.

Sources

All sources opened and checked on 11 October 2026.

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