Permitted development for larger rear extensions

A single storey rear extension of up to 8 metres on a detached house, or 6 metres on any other house, is permitted development under Class A of the General Permitted Development Order 2015 provided you first go through the neighbour consultation scheme. Larger rear extension prior approval is not a planning application. The council cannot refuse it on design, policy or highway grounds. It can only refuse if an adjoining owner or occupier objects and the council then concludes that the effect on the amenity of adjoining premises is unacceptable.

The right does not apply on designated land, so a conservation area, National Park, National Landscape, the Broads or a World Heritage Site rules it out entirely.

What the larger extension right permits

The ordinary Class A limits for a single storey rear extension are 4 metres for a detached house and 3 metres for any other house. The larger extension provisions double those to 8 and 6 metres respectively, subject to the prior approval procedure.

The other limits stay in place:

• Maximum height of 4 metres overall.
• Where the extension is within 2 metres of a boundary of the curtilage, the eaves height must not exceed 3 metres.
• Single storey only.
• The extension must not extend beyond a wall forming the principal elevation, or a side elevation fronting a highway.
• Materials must be similar in appearance to those of the existing house.
• No verandas, balconies or raised platforms.
• Together with other buildings, the development must not cover more than half the area of the curtilage surrounding the original dwellinghouse.

Original dwellinghouse means the house as first built or as it stood on 1 July 1948. A previous owner's extension counts against you even though you never built it.

Measuring the depth

Depth is measured from the rear wall of the original dwellinghouse, not from the current rear wall. A house that already has a 3 metre extension has used part of the allowance.

That single point causes more failed notifications than anything else. Before anything is drawn, establish what the original house looked like. Historic mapping, an old sale plan, the council's own planning history and the building's fabric all help.

Measure externally, and measure at the deepest point. Where the rear elevation steps, the projection is measured from each part of the original rear wall it projects beyond.

The neighbour consultation scheme, step by step

1. Submit to the local planning authority a written description of the proposed development, including how far it extends beyond the rear wall, the maximum height and the eaves height, a plan showing the site and the proposed development, the addresses of all adjoining premises, and your contact address, with the fee.
2. The authority notifies the owners and occupiers of adjoining premises, meaning those sharing a boundary with the application site, giving them 21 days to object in writing.
3. If no objections are received within the 21 days, the authority notifies you that prior approval is not required and you may build.
4. If any objection is received, the authority must consider the impact of the proposed development on the amenity of all adjoining premises, and decide whether to grant or refuse prior approval.
5. The authority has 42 days from receipt of a valid application to notify its decision. If it does not, you may proceed as described.

Refusal carries a right of appeal to the Planning Inspectorate. A refusal is not a refusal of planning permission, so a full householder application remains available as an alternative route.

What neighbours can and cannot object about

The only consideration is the impact on the amenity of adjoining premises. In practice that means loss of light, loss of outlook, and an overbearing or enclosing effect, assessed for the properties that share a boundary.

Objections about the appearance of the extension, about construction noise and dust, about parking during the works, about party wall matters, about drainage, about loss of a view, or about devaluation of a neighbouring property are all outside the scope. So is an objection from someone who does not occupy adjoining premises.

That narrowness is the strength of the route and also its risk. A single objection from a neighbour on the darker side of the house forces a judgement on light and outlook, and the officer will usually apply a daylight test. Where light is marginal, a short daylight and sunlight assessment applying the established methodology answers the question rather than leaving it to impression.

Talking to the neighbours before submitting is worth more than any drawing. Most objections come from surprise rather than from harm.

Designated land and other exclusions

The larger extension right is not available on article 2(3) land. Check the designation before doing anything else, because the mapping is not always obvious at street level and conservation area boundaries frequently run down the middle of a road.

An Article 4 direction can remove the right in an area that is not designated land, and many authorities have made directions covering estates of consistent character. The right is also unavailable on a flat or maisonette, on a building that is not a dwellinghouse, and where permitted development rights have been removed by condition on the original planning permission. Reading the conditions on the permission that created the house is a two minute job that saves weeks.

Listed buildings are a separate matter again: the works may be permitted development for planning purposes and still require listed building consent, which brings the significance of the building into play and usually means a Heritage Statement is needed.

Notifying completion

The right carries a condition requiring the developer to notify the local planning authority in writing that the development has been completed, as soon as reasonably practicable after completion.

The notification must include the name of the developer, the address of the building, and the date of completion. It is a small administrative step that people skip, and it matters when the house is sold, because a conveyancer will look for evidence that the conditions attached to the permitted development were met.

Keep the notification letter, the council's confirmation that prior approval was not required, and the drawings you submitted, together in one file. That bundle is what a buyer's solicitor will ask for.

When a full application is quicker

Prior approval takes up to 42 days and cannot be refused on design. A householder application takes up to eight weeks and can be refused on anything.

Use the full application route where the scheme is wider than the permitted development limits, where it includes a roof alteration, a balcony or a side extension, where the house sits on designated land, where permitted development rights have been removed, or where the extension needs to exceed 4 metres in height.

Also consider it where you already know a neighbour will object. If an objection is inevitable, the council will be making an amenity judgement either way, and a full application lets you present the design case properly rather than being confined to the narrow prior approval test.

Check whether the house is on designated land, work out the depth of the original rear wall, then decide the route. If you need supporting material for the application, you can see which documents a householder scheme usually needs before you commission anything.

This is general guidance, not legal advice. A lawful development certificate is the only formal way to confirm that works are lawful, and permitted development limits are detailed and change from time to time. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.