Most single storey rear extensions on London houses can be built without a full planning application, but the rules are tighter than many homeowners expect, and the capital's conservation areas and Article 4 directions catch people out every week. This guide sets out what you can build under permitted development, where the limits sit, and when you will need to apply to your borough before a spade goes in the ground.
Permitted development rights let owners of houses (not flats or maisonettes) extend within set limits without a planning application. For a single storey rear extension on a terraced or semi detached house, the standard limit is 3 metres beyond the original rear wall. On a detached house it is 4 metres. The extension must be no higher than 4 metres to the ridge, with eaves no higher than 3 metres if it sits within 2 metres of a boundary.
The larger home extension scheme, often called prior approval, stretches those limits to 6 metres for terraced and semi detached houses and 8 metres for detached. It is not automatic. You notify the council, they write to your neighbours, and if anyone objects the council decides whether the impact on neighbours is acceptable. In tightly packed London streets such as Walthamstow, Tooting or Ealing, an objection from next door is common, so allow for the 42 day process before you commit to a builder's start date.
Around a third of London homes sit inside a conservation area, and many boroughs such as Camden, Islington, Richmond and Kensington and Chelsea have Article 4 directions that remove some or all permitted development rights. In these areas a side extension, a rear extension of any size or even new cladding may need a full application. Listed buildings always need listed building consent for external alterations, regardless of size.
Flats, maisonettes and houses converted into flats have no permitted development rights at all, so every extension needs an application. The same applies if a previous owner already used up the allowance. A loft dormer built in 2010 still counts against the volume limits today, and a rear extension added before you bought the house sets the new baseline for what counts as the original rear wall.
Check your borough's planning portal before designing anything. Searching your postcode on the council's interactive map will show conservation areas, Article 4 directions and listed status in a few minutes. If the map is unclear, a Lawful Development Certificate costs roughly half the fee of a full application and gives you written proof that the work is lawful, which matters when you come to sell.
A householder planning application in England currently carries a fee in the region of £250 to £300, with the council targeting a decision within 8 weeks. On top of that you will need measured drawings of the existing and proposed house, usually prepared by an architect or architectural technician. In London expect to pay somewhere between £1,500 and £4,000 for drawings suitable for planning, depending on the complexity and whether structural details are included.
Planning permission is only part of the picture. Every extension, whether it needed planning or not, must comply with Building Regulations. That means either a full plans application or a building notice to the council's building control team or an approved inspector, covering structure, insulation, fire safety, drainage and ventilation. If your extension sits on or near the boundary you will also need to serve Party Wall notices on neighbours, typically two months before work starts for a new wall or excavation.
The most expensive error is starting work on the assumption that a build falls within permitted development when a small detail pushes it over the line. Eaves that are 3.2 metres high instead of 3, or a flat roof that wraps around a side return and turns a rear extension into a wraparound, both take the project outside the rules. Retrospective applications are possible but stressful, and if refused the council can serve an enforcement notice requiring demolition.
The second mistake is ignoring the original house baseline. Permitted development measures from the house as it stood on 1 July 1948 or when first built if later, not from what is there today. On many Victorian terraces the existing outrigger already extends back several metres, so the 3 metre allowance may be far smaller than expected once measured correctly.
Not usually on a house outside a conservation area, provided it stays within 3 metres for terraced and semi detached houses or 4 metres for detached, and meets the height and materials rules. Extensions up to 6 or 8 metres need prior approval through the neighbour consultation scheme.
A householder application has a statutory 8 week target, though busy London boroughs sometimes take longer. Prior approval for a larger extension takes 42 days, and a Lawful Development Certificate is typically decided within 8 weeks as well.
No. Flats and maisonettes have no permitted development rights for extensions, so any extension needs a full planning application. You will also usually need consent from the freeholder or management company under the terms of your lease.
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