Do I Need Planning Permission for a Rear Extension in London?

If you're thinking about extending the back of your London home, this is usually the first question that comes up — and the honest answer is: it depends. Many rear extensions in London can be built without a full planning application, under what's known as permitted development. But the rules are specific, they vary depending on your property type, and a surprising number of projects trip up on a detail homeowners didn't know applied to them. Here's what actually determines whether you need planning permission, and where the common mistakes happen.

What "permitted development" actually means

Permitted development rights allow certain home improvements to go ahead without a full planning application, provided the project stays within set limits on size, height, and position. These rights come from national planning law, not from your local council directly — but individual councils can still remove or restrict them in certain areas, which is where a lot of confusion starts.

If your project falls within the limits, you'll still need Building Regulations approval to make sure the construction itself is safe and compliant — permitted development only removes the need for planning permission, not the need for the build to meet building standards.

The depth and height limits that matter most

For a single-storey rear extension, the standard permitted development limits are:

• Up to 3 metres deep from the original rear wall for semi-detached and terraced houses

• Up to 4 metres deep for detached houses

• Maximum height of 4 metres overall

• Maximum eaves height of 3 metres if the extension is within 2 metres of a boundary

There's also a larger, less commonly used route — the Larger Home Extension Scheme — which allows greater depths (up to 6 metres for semi-detached/terraced, or 8 metres for detached) through a "prior approval" process. This involves notifying your neighbours and giving the council a short window to raise concerns, rather than a full planning application. It's quicker than full planning, but it isn't automatic — the council can still object based on neighbour impact.

Two-storey rear extensions are treated differently and generally fall outside permitted development altogether, meaning they almost always require a full planning application regardless of size.

Where homeowners get caught out

The depth and height numbers above get most of the attention, but several other conditions have to be met simultaneously — miss any one of them and the whole project falls outside permitted development, no matter how modest the extension looks:

• Roof pitch and materials generally need to match the existing house where the extension is visible from the street

• Side extensions and rear extensions built together (wraparounds) usually push the project past permitted development limits and into full planning territory

• Proximity to the rear boundary matters for larger schemes — extensions using the Larger Home Extension route typically can't come within 7 metres of the rear boundary

• Volume limits apply on top of the depth and height rules, particularly relevant if you're combining a rear extension with other works

The exceptions that override everything else

Regardless of size, permitted development rights don't apply — or are restricted — in certain situations:

• Conservation areas often have reduced permitted development rights, particularly around materials and side extensions

• Article 4 Directions are used by some councils to remove permitted development rights entirely in specific streets or areas — these are common in parts of London and easy to miss if you haven't checked

• Listed buildings always require planning permission (and often listed building consent) for any extension, regardless of size

• Flats and maisonettes don't benefit from the same permitted development rights as houses — almost all extensions to flats need a full planning application

This is exactly where London projects differ most from a generic national guide: a Victorian terrace in a conservation area in Clapham and a similar terrace two streets over with no restrictions can be subject to completely different rules, even though the properties look identical.

Even where planning permission isn't legally required

It's worth applying for a Lawful Development Certificate even when you're confident your project falls within permitted development. It isn't a legal requirement, but it gives you a formal, council-issued confirmation that the work is lawful — which matters for mortgage lenders, and for any future buyer's solicitor, when you come to sell.

Thinking about a rear extension? Book a free 20-minute consultation and we'll give you a straight answer on what your property qualifies for, before you spend anything on design. Book Your Free Consultation