House Extension Planning Permission in London
Many houses in East and North London can add a rear extension without applying to the council. House extension planning permission in London only becomes necessary once a project goes beyond the size limits for permitted development, which means building work you can do without a council application, or when stricter local rules apply. Work out which category you are in before design starts and you avoid the slow, expensive surprises.
Do You Need Planning Permission for a House Extension?
For a single-storey rear extension on a typical terraced or semi-detached house, probably not. The main permitted development limits are 3 metres behind the original rear wall for a terrace or semi, and 4 metres for a detached house. Beyond those limits, a separate route called the Larger Home Extension scheme allows you to go up to 6 metres on a terrace or semi and 8 metres on a detached house. That requires notifying the council and giving neighbours the chance to object, but it is not a full planning application. Most go through without issue, provided no conservation area restrictions apply.
The table below covers the situations we see most often across the boroughs we work in. Treat this as a starting point, not a ruling. The limits measure from the original rear wall as built, which matters if a previous owner has already extended.
Planning Overview
Your situation
Single-storey rear extension within PD limits (3m terrace/semi, 4m detached)
Single-storey rear extension up to 6m (terrace/semi) or 8m (detached)
Single-storey rear extension beyond those limits
Double-storey rear extension
Side extension
Front extension facing the road
Extension covering more than half the garden
Property in a conservation area
Property under an Article 4 direction
Flat or maisonette
Listed building
Planning permission usually needed?
No
Prior approval under Larger Home Extension scheme
Yes
Yes
Yes
Yes
Yes
Usually yes
Yes
Yes, always
Yes, plus listed building consent
Planning Permission Details
What Permitted Development Actually Covers
When You Need a Full Planning Application
Permitted development lets you extend without a planning application, provided you stay within those size limits. The extension cannot be higher than 4 metres, or 3 metres within 2 metres of a boundary. Side extensions must be single storey, no wider than half the original house, and cannot face a highway. No extension can cover more than half the total garden area. These rules exist to keep changes in proportion with the street.
House extension planning permission is required once your project goes beyond permitted development or prior approval. The common triggers are double-storey extensions, side extensions on corner plots, anything that faces the road, and extensions that push past the maximum depths. Flats and maisonettes have no permitted development rights at all. A full application takes around eight weeks for the council to decide, and that clock does not start until the design is submitted. Finding out you need one after the drawings are done costs more than finding out before.
Conservation Areas and Article 4 Directions
Building Regulations Apply Either Way
London is where this gets complicated. Hackney, Islington and Waltham Forest all have conservation areas, where the council protects the character of the streets and removes some permitted development rights. Extensions that would go through automatically elsewhere often need permission here, and changes visible from the road face closer scrutiny. Some streets also carry an Article 4 direction, a rule that switches off permitted development rights for a defined area. Each borough runs its own planning department and they do not all read the rules the same way. An extension that sails through in Leyton can face a different conversation in Stoke Newington.
Planning permission and building regulations are two different things, and people confuse them regularly. Planning is about whether you are allowed to build. Building regulations are the safety rules every extension must meet: structural loads, insulation, drainage, fire safety, and the steelwork needed when load-bearing walls come down to create an open plan. Even when you do not need planning permission, you always need building control sign-off. We manage those submissions as part of the work.
Party Wall Agreements
If your extension touches a wall you share with a neighbour, or involves excavation within 3 to 6 metres of their foundations, you need a party wall agreement. That is the legal paperwork your neighbour signs before work begins. It has nothing to do with the council, but it carries its own notice periods. Side return extensions and rear extensions running close to the boundary almost always trigger this. We start the process early and handle the paperwork for you.
How LLAC Handles Planning in Your Borough
We have built extensions across East and North London for 25 years. Before design starts, we check your remaining permitted development allowance, whether your street sits in a conservation area, and whether prior approval or a full application is needed. That information shapes the brief before it becomes expensive to change. Where a full application is needed, we work with local planning consultants who know the borough’s policies and handle the submissions. If you want a sense of what the build will cost alongside the planning picture, our house extension cost guide sets out realistic 2026 figures.
If you are weighing up an extension and want to know where you stand on planning, get in touch. We will check what is possible for your home and your borough before you commit to a design.