Planning permission is one of the first things homeowners ask about when they start thinking about an extension — and it’s also one of the most misunderstood. The honest answer is that many South London extensions don’t need a planning application at all. But the rules are specific, and getting it wrong can create serious problems. This guide explains exactly how planning permission works for house extensions across South London, what permitted development allows, and when you need to make a full application.
What is Permitted Development?
Permitted development is a set of national planning rules that allow certain types of building work to be carried out without a planning application. The government introduced permitted development rights to remove unnecessary bureaucracy from straightforward home improvements — and extensions are explicitly covered.
Under permitted development, you can build a rear extension on your property without applying to the council, provided the extension meets a set of size, height, and design criteria. These rules apply across England — including South London — though some properties and areas are excluded.
The key point: permitted development is not automatic permission to build anything. It’s permission to build within defined limits. Exceed those limits and you need a full planning application.
What Can You Build Under Permitted Development in South London?
For a typical terraced or semi-detached house in South London — outside a conservation area and with no Article 4 Direction in force — you can build:
Single Storey Rear Extensions
- Up to 3 metres beyond the original rear wall (terraced and semi-detached houses)
- Up to 4 metres beyond the original rear wall (detached houses)
- Maximum height of 4 metres
- Must not exceed the height of the existing roof
Larger Home Extension Scheme
Through the Larger Home Extension Scheme (sometimes called the Prior Approval process), you can extend further:
- Up to 6 metres beyond the original rear wall (terraced and semi-detached)
- Up to 8 metres (detached houses)
This requires a prior approval application to the council — simpler than full planning but not as straightforward as standard permitted development. Neighbours are notified and can object.
Side Extensions
Single-storey side extensions are permitted under PD if:
- No wider than half the width of the original house
- No higher than 4 metres
What Permitted Development Does NOT Cover
- Double storey extensions (always require planning permission)
- Any extension that exceeds the size limits above
- Extensions that cover more than 50% of the original garden area
- Extensions on flats or maisonettes
- Extensions where the property’s PD rights have been removed
When Do You Need Full Planning Permission
You’ll need to make a full planning application to your local council when:
Your Extension Exceeds Permitted Development Limits
The most common reason. If you want a rear extension deeper than 3 metres on a terrace, or any double storey extension, you need full planning permission.
Your Property is in a Conservation Area
South London has an exceptionally high number of conservation areas — Bromley has around 40 alone. If your property is within a conservation area, some permitted development rights are reduced or removed entirely. Side extensions, for example, are not permitted development in most conservation areas regardless of size.
An Article 4 Direction Applies to Your Property
An Article 4 Direction is a specific planning rule that removes some or all permitted development rights from a defined area. Several South London conservation areas have Article 4 Directions in place — including parts of the Progress Estate in Eltham, areas in Beckenham’s Cator Estate, and Brockley in Lewisham. If an Article 4 Direction applies to your street, extensions that would normally be permitted elsewhere require a full planning application.
Your Property is Listed
Listed buildings require listed building consent for any extension, regardless of size. Greenwich, in particular, has a high concentration of listed residential properties — especially around the town centre and Greenwich Park.
Your Property is a Flat or Maisonette
Permitted development rights don’t apply to flats or maisonettes. Any extension to a flat requires full planning permission.
South London Planning Authorities — What to Expect
South London spans multiple planning authorities, and each has its own approach.
London Borough of Bromley
Bromley is one of the greenest and most suburban of the South London boroughs, and its planning policy reflects that. The council places strong emphasis on protecting suburban character — particularly in Beckenham, Bromley town, and the many conservation areas across the borough. Applications for larger or more visible extensions receive close scrutiny.
Royal Borough of Greenwich
Greenwich’s planning context is shaped by the UNESCO World Heritage Site designation covering the maritime town centre. Extensions within or near the WHS setting receive additional scrutiny, and the heritage team is involved in applications affecting listed buildings or conservation areas. Outside the heritage areas, Greenwich Council processes most household applications within the standard 8-week timeframe.
London Borough of Lewisham
Lewisham has significant conservation areas including Brockley, Telegraph Hill, and Hither Green. The council’s planning team is generally pragmatic on permitted development applications but applies consistent design standards to full applications, particularly in conservation areas.
How to Check if You Need Planning Permission
Before starting any design work, check the following for your specific property:
- Is your property in a conservation area? Check your local council’s interactive map (available on all South London council websites).
- Is there an Article 4 Direction on your street? Also available on council planning portals.
- Is your property listed? Check the Historic England listed buildings register.
- What are the original dimensions of your property? Permitted development limits are calculated from the original house — any previous extensions already use up some of that allowance.
If you’re unsure, a planning consultant or experienced builder can check this for you before any money is spent on design.
What Happens if You Build Without Permission?
Building without the required planning permission — or outside permitted development limits — is a serious problem. The council can issue an enforcement notice requiring you to demolish the extension and restore the property to its original condition. This is expensive, disruptive, and entirely avoidable.
It also creates problems at sale. Solicitors routinely check whether extensions have the necessary permissions, and an unpermitted extension can delay or kill a sale — or require you to take out indemnity insurance as a condition of completion.
Always confirm the planning position before building.
We Check the Planning Position for Every Project
At Kelmend Construction, we check the specific planning position for every property we visit — conservation area status, Article 4 Directions, permitted development limits, and any previous extensions that affect the available allowance. We tell you exactly what planning route applies to your project before any design work begins, so there are no surprises.
We cover Bromley, Greenwich, Lewisham, Eltham, Beckenham, and the surrounding South London area. Get in touch for a free, no-obligation consultation. If you’re also researching costs, see our guide to house extension costs in South London.