Do I need planning permission for a rear extension?

Permitted development is a set of national rights in the General Permitted Development Order 2015 that let a house be extended without a planning application. Class A of Part 1 covers extensions, and an extension has to pass every one of its tests, not just the depth one.

Every limit is measured from the original house: the house as it stood on 1 July 1948, or as first built if later. An earlier extension counts against the allowance even if a previous owner built it, so a house with an old back addition may have used part of its depth already. A house created by a change of use, such as an office conversion, has no Class A rights at all.

Terraced, end-of-terrace and semi-detached houses share one set of depth limits; detached houses get a metre more.

Prior approval is the middle route. A single-storey rear extension deeper than the standard limit, up to 6 m on an attached house or 8 m on a detached one, can still be permitted development, but only after the council has been notified and has had the chance to object (GPDO 2015 Sch. 2 Pt 1 A.1(g) and A.4). It is not a planning application: the council does not reopen the principle of the extension, only its effect on the neighbours.

This is the neighbour consultation scheme. You send the council a plan showing the depth, height and eaves height, with the fee of £249. The council writes to the adjoining neighbours, who can comment. The council has 42 days to decide; if it gives no decision in that time, the extension can go ahead as notified. Work should not start before the decision or the end of the 42 days. The route is not available in a conservation area.

A conservation area is article 2(3) land, and Class A is narrower there. A single-storey rear extension within the standard 3 m or 4 m remains normally permitted development, subject to the limits checked in the report. The larger home extension route is not available, so anything deeper needs a planning application. Rear extensions of more than one storey are excluded (GPDO 2015 Sch. 2 Pt 1 A.2(c)), as are side extensions (A.2(b)) and cladding the outside of the house (A.2(a)).

An Article 4 direction is a council order that removes some permitted development rights in a defined area. Many London directions concern other things, such as converting houses into shared homes, but some remove Class A, and then every rear extension in the area needs a planning application. The direction's text says which rights it removes. Open data on Article 4 covers only about half of London's boroughs, so check with the council before relying on a clear result.

Flats and maisonettes have no householder permitted development rights: Part 1 applies to houses only. Any extension to a flat needs a planning application, with the same council fee of £548, and the freeholder's consent under the lease as well. A house converted into flats counts as flats for this, even if it still looks like one house from the street.

It can be, but the limits are tight. A rear extension of more than one storey may project no more than 3 m beyond the original rear wall and must stay at least 7 m from the rear boundary (GPDO 2015 Sch. 2 Pt 1 A.1(h)). Its roof pitch should match the house's (A.3(c)), and upper-floor side windows must be obscure-glazed. There is no larger home extension route for two storeys, and none at all in a conservation area (A.2(c)).

The eaves rule catches most London terraces: within 2 m of a boundary the eaves may be no higher than 3 m (A.1(i)), which a second storey against a neighbour's wall cannot meet. The report prices a double-storey rear extension at about 3 m deep unless you give a depth, within the 3 m limit, but the boundary distance and eaves still have to be measured.

A lawful development certificate for a proposed extension is the council's written confirmation that the design is permitted development. It is optional, but it turns a screening result into a decision. The council fee is £274, plus the Planning Portal charge of £85 if you apply through the portal.

It is worth having for three reasons. Buyers' solicitors ask for proof that an extension was lawful, and a certificate answers in one page. It protects against a neighbour's complaint or enforcement later. And it settles the hard cases, such as a depth close to the limit or an earlier extension, before the build starts. On the prior approval route, the council's prior approval decision serves as the written record instead.

For a single-storey rear extension on a two-storey mid-terrace house, priced at about 3.5 m deep when no depth is given, the screen's route is: larger home extension: prior approval needed. The council fee for that route is £249. The checks behind it are conservation area (to measure or confirm; planning.data.gov.uk); rear projection (to measure or confirm; GPDO 2015 Sch. 2 Pt 1 A.1(g), A.4); height (to measure or confirm; GPDO 2015 Sch. 2 Pt 1 A.1(f), A.1(i)); half the garden (to measure or confirm; GPDO 2015 Sch. 2 Pt 1 A.1(b)); materials (to measure or confirm; GPDO 2015 Sch. 2 Pt 1 A.3(a)).

A pass means nothing in the answers or the open data rules the point out; a check means it has to be measured on the drawings or confirmed with the council. With your own address and depth the report runs the same checks against the planning registers for your street. The screening is against published rules, and the council decides.

House extension costs, the planning route and a timeline in each London borough.

Barking and Dagenham · Barnet · Bexley · Brent · Bromley · Camden · Croydon · Ealing · Enfield · Greenwich · Hackney · Hammersmith and Fulham · Haringey · Harrow · Havering · Hillingdon · Hounslow · Islington · Kensington and Chelsea · Kingston upon Thames · Lambeth · Lewisham · Merton · Newham · Redbridge · Richmond upon Thames · Southwark · Sutton · Tower Hamlets · Waltham Forest · Wandsworth · Westminster

How far can I extend under permitted development?

For a single-storey rear extension, 3 m beyond the original rear wall on a terraced or semi-detached house and 4 m on a detached one (GPDO 2015 Sch. 2 Pt 1 A.1(f)). With prior approval, up to 6 m and 8 m (A.1(g) and A.4), outside a conservation area. Any earlier extension counts against those depths, and the half-garden, height and eaves limits still apply.

What is the neighbour consultation scheme?

It is the prior approval process for a larger home extension. You notify the council with a plan and the fee of £249; the council consults the adjoining neighbours and has 42 days to decide. It considers only the effect on the neighbours. If it gives no decision within the 42 days, the extension can be built as notified.

Do I need building regulations approval as well as planning?

Yes. Planning and building regulations are separate. Every extension needs building control approval for its foundations, structure, insulation, drainage and fire safety, whichever planning route it takes. The council's building control fee for an extension is typically £1,000 to £1,800. Keep the completion certificate; it is needed when you sell.