Permitted development or planning permission?

Most homeowners are asking one of two very different questions when they ask this. The first is "am I allowed to do it at all". The second is "do I have to ask anyone first". Permitted development answers the second, not the first. It is not a loophole and it is not permission-lite. It is a national grant of planning permission, already given, for a defined list of things — which means if your project fits inside the list, you have permission the day you decide to build.

The catch is that the list is written in dimensions, and houses are not. Almost every conversation we have about permitted development ends up being about a single measurement: a boundary two metres away, an eaves line, a strip of garden that was built over in 1994 and now counts against you.

What permitted development actually covers

For a house — not a flat — the householder permitted development rights cover, broadly, single-storey rear extensions, side extensions, loft conversions, rooflights, porches, outbuildings, and various bits of external work like re-rendering. Each has its own class in the legislation and each has its own conditions.

The ones that matter most on a London street:

• Single-storey rear extension. Up to three metres deep on a terrace or semi, four on a detached house, with a maximum height of four metres. There is a separate prior-approval route — the larger home extension scheme — that doubles those depths to six and eight, but it requires you to notify the council, who write to your neighbours, who get a period to object. It is not automatic and it is not instant.
• Eaves near a boundary. If any part of the extension sits within two metres of a boundary, its eaves cannot exceed three metres. On a narrow terrace this is the rule that shapes the roof, and it is why so many side returns end up with a mono-pitch or a flat roof with rooflights rather than the pitched roof people picture.
• Side extension. Single storey only, four metres maximum height, and no wider than half the width of the original house. That last clause is the one that quietly kills full-width side returns on wide plots.
• Loft conversion. An added volume of up to 40 cubic metres on a terrace or 50 on a semi or detached — measured as an allowance for the house, not for you, so a previous owner's dormer eats into it. Nothing may sit above the existing ridge, and nothing may project beyond the roof plane on the elevation facing a highway. That is why front dormers are almost always a planning application and rear dormers usually are not.

Two conditions cut across all of them. Materials must be similar in appearance to the existing house, and the extension plus any existing outbuildings must not cover more than half the land around the original house — original meaning as first built, or as it stood on 1 July 1948 if it is older than that. If someone extended in 1998, you inherit the consequences, not a clean sheet.

What takes permitted development away

Permitted development is a default, and defaults get removed. In London the four common removals are:

• You live in a flat or maisonette. Flats have no householder permitted development rights of any kind. A rear extension on a ground floor flat is a full planning application, always, however modest.
• An Article 4 direction. A council can withdraw specific permitted development rights across a defined area — usually a conservation area or a coherent run of period streets. Richmond and Merton both use them extensively. Two houses on the same road can sit either side of the boundary line.
• A conservation area. Side extensions and rear extensions of more than one storey are excluded outright, cladding is excluded, and roof extensions — the whole of the loft conversion class — are not permitted at all.
• A planning condition on an earlier consent. Newer estates and any house created by a conversion frequently have permitted development removed by condition. It is written into the original decision notice and almost nobody reads it before they start.

Listed buildings sit in their own category. Listed building consent is a separate regime that applies to internal work as well as external, and permitted development is irrelevant to it.

The certificate people skip

If your project is permitted development, you can build it without telling the council anything. You can also apply for a lawful development certificate, which is the council formally confirming your reading of the rules was correct. It costs roughly half a householder planning fee and takes about eight weeks.

We recommend it on almost every job, for one unglamorous reason: you will sell this house one day, and the buyer's solicitor will ask what authorised the extension. "It was permitted development" is an opinion. A certificate is a document. Without one, the usual fix is an indemnity policy negotiated in the last fortnight before exchange, at your expense, under time pressure.

Planning permission is not the disaster people expect

A householder planning application takes eight weeks from validation, costs a few hundred pounds in fees, and is decided against the local plan and any supplementary design guidance. It is not a judgement on your taste. Most refusals we see come down to the same short list — loss of light to a neighbour, an unbroken run of terrace roofline being interrupted, or a design that ignores the borough's own guidance on rear extension depths in that character area.

All of which is knowable in advance. Councils publish their design guidance, every neighbouring decision is on the planning portal, and a pre-application enquiry buys an officer's written view before you commit to drawings.

Building regulations are a separate thing entirely

This is the single most common misunderstanding we meet. Permitted development means you do not need planning permission. It has no bearing on building control. Structure, fire escape, insulation, drainage, ventilation and electrical safety are all governed by the building regulations, and they apply to a permitted development extension exactly as they apply to one with full planning consent. Two different regimes, two different sets of paperwork, both mandatory.

The Party Wall etc. Act 1996 is a third, and is not part of either.

Where this lands in practice

On a Wandsworth terrace, a three-metre rear extension and a rear dormer are usually both permitted development, and the whole job proceeds without a planning application. On the same terrace inside a conservation area, the dormer becomes an application and the side return may become one too. On a Herne Hill ground floor flat, neither is permitted development and the lease matters as much as the planning.

We work this out on the survey, before anything is drawn. It takes an hour and it decides the shape of the next six months.