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

What permitted development allows

Permitted development (PD) rights let you extend a house without applying for planning permission, as long as you stay within set limits. They only apply to houses. Flats and maisonettes have no PD rights, so any extension to a flat needs full planning permission.

All depths are measured from the rear wall of the original house, meaning the house as it was first built or as it stood on 1 July 1948. If a previous owner has already extended, that extension uses up some or all of your allowance.

• Single storey: up to 3m deep for terraced and semi-detached houses, or 4m for detached houses
• Maximum height of 4m, and no more than 3m to the eaves if you build within 2m of a boundary
• Extensions and outbuildings together must cover no more than half the land around the original house
• Two storey: up to 3m deep, at least 7m from the rear boundary, with a roof pitch matching the house and any upper side windows obscure glazed and fixed below 1.7m
• Materials should look similar to the existing house
• No balconies, raised platforms or verandas

Going deeper with prior approval

The larger home extension scheme lets a single storey rear extension go up to 6m deep on terraced and semi-detached houses, or 8m on detached houses. It is not a planning application but it isn't automatic either. You notify the council, they write to your neighbours, and if anyone objects the council judges the effect on their light and privacy.

The council has 42 days to decide, and you must not start work until you have their approval or that period passes with no decision. The fee is modest compared with a full application, but check your council's current fee on the Planning Portal because fees change.

Common London situations that change the answer

A large share of London's housing stock is in conservation areas or covered by Article 4 directions, and these catch out many homeowners. In a conservation area you can't build a rear extension of more than one storey under PD, the larger home extension scheme isn't available, and cladding the extension isn't allowed. An Article 4 direction can remove PD rights altogether, so check your council's website or phone the planning department.

Other things to check:

• Listed buildings need listed building consent for almost any extension, whatever its size
• Newer houses and estates sometimes had PD rights removed by a condition on the original planning permission
• Wraparound extensions that combine a side return and a rear extension, popular on Victorian terraces, often exceed PD limits and usually need full planning
• Side return infills must be single storey, no taller than 4m, and no wider than half the original house

Getting certainty before you build

Even if your plans fit within PD, we recommend applying for a Lawful Development Certificate. It costs half the normal planning fee, typically takes around eight weeks, and gives you written proof that the work was lawful. That proof matters when you sell, as buyers' solicitors will ask for it.

If you do need full permission, a householder application usually takes eight weeks from validation, although some London boroughs take longer. Allow extra time for drawings, and for any changes the planning officer asks for. Most straightforward single storey rear extensions that respect neighbours' light get approved.

Planning is only one of the approvals

Planning permission or PD covers whether you're allowed to build. Building Regulations approval is a separate requirement for every extension, covering structure, insulation, drainage and fire safety, and it applies even when no planning is needed.

In London terraces and semis, the Party Wall etc. Act 1996 almost always applies too. You must serve notice on neighbours at least two months before building on or at the boundary, or one month before digging foundations within 3m of their property. Leave time for this, because a neighbour who disagrees can hold things up while surveyors agree an award.