Planning Permission for Extensions

Find out whether your home extension project needs planning permission and how to secure local authority consent
by Chris Bates
6th August 2018

Not every project needs formal consent and in fact many extensions are achieved under permitted development (PD) rights. This can save you considerable time at the planning stages, not to mention money on the application fee.

Some pretty sizeable home extension projects are possible under permitted development, especially in England, where the restrictions have been relaxed subject to a prior approval procedure.

Currently in England, single-storey extensions to the rear of a house can be 3m deep for terraces and semi-detached homes, or 8m deep for detached houses.

Do I need planning permission for an extension?

If your scheme fits within these parameters, there’s a good chance it will be allowable as permitted development:

  • Extensions (including previous additions) and other buildings must not exceed 50% of the total land area around the original house.
  • You cannot extend forward of the main elevation (or the side elevation where it fronts the highway).
  • Single-storey rear additions must not extend beyond the rear of the original house by more than 3m for terraces and semi-detached homes, or by 4m for detached houses.
  • Side extensions must be single storey with a maximum height of 4m and must be no greater than half the width of the original house.
  • Extensions within 2m of a boundary should have a maximum eaves height of no more than 3m.
  • Multi-storey extensions should have a maximum eaves and ridge height no taller than the existing house, with a matching roof pitch.
  • A multi-storey addition cannot extend beyond the rear wall of the original house by more than 3m or be within 7m of any boundary opposite the rear wall.
  • Any windows on upper floors of side elevations must be obscure-glazed and non-opening (unless the openable part is at least 1.7m above floor level).
  • You must use external materials that are similar in appearance to the existing house (unless you’re adding a conservatory).
  • PD rights do not apply in designated areas or to listed buildings.

Your architect, designer or main contractor should be able to advise on whether your scheme meets the permitted development criteria – but it’s often worth checking back with the local authority’s planning department.

You may want to apply for a certificate of lawful development, which can come in handy for proving the project complies should you sell the house further down the line.

Quick guide: Extended permitted development rights in England

Homeowners in England can currently benefit from relaxed permitted development rules, which allow single-storey rear extensions up to 8m from the rear wall for detached houses, and up to 6m for terraces and semi-detached properties.

The scheme requires you to notify your local authority with some basic details of the scheme (find out more at but there’s no fee to pay.

The council will then invite neighbours to comment – but providing there are no material objections under planning law, the scheme should be rubber stamped.

If you need to make a full planning application for your extension, then it’s worth taking a look at your council’s Local Plan. This will have a big influence on the planning department’s final decision on the outcome of your application.

Be aware that the language in a Local PLan can be vague, which can mean that different planners will interpret things differently.

Depending on the type of project you’re undertaking and how close it is to neighbouring properties, the Party Wall Act may also apply. If it does, you’ll need to inform the affect neighbours of your plans should they involve a joint wall or boundary, or if works would occur near or beneath the property’s foundations.

Building Regulations for extensions

Almost every type of extension will require formal Building Regulations approval. The only exception is for conservatories, which can be exempt provided they meet the following criteria:

  • The conservatory is built at ground floor level and has a floor plan of less than 30m2
  • It is separated from the house by external-quality doors
  • The conservatory has its own independent heating system, seperate from the main house

Note that the glazing and electrical installations must meet Building Regulations standards; and that any new openings formed to the conservatory will require formal approval.

There are two main routes to securing Building Regulations approval for other types of extension:

Route 1: Full plans application

The first option is to submit a full plans application. This way, you get the structural details for your extension drawn up professionally and scrutinised by building control before you actually start work.

This gives you the advantage of being able to submit detailed drawings when you put the project out to tender, so quotes should be accurate and easy to compare. You will also have these drawings to refer back to during the construction process.

Route 2: Building notice

The alternative is to serve a building notice 48 hours before work commences on site. This can be a quicker and more cost-effective option when tackling very straightforward projects, as it doesn’t require detail drawings.

For any extensions that is complex or high-value, a full plans Building Regulations application is usually the way to go. In either case, the work will be checked at key stages by building control or an approved inspector.

Assuming that all goes well, you’ll be issued a completion certificate at the end of the scheme. Be sure to keep this safe: it is your proof that the project does indeed meet the minimum construction standards to minimise noise transfer between rooms and storeys.

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