Prior Approval for a Larger Home Extension: How It Works [2026]

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Prior Approval for a Larger Home Extension: How It Works

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November 5, 2026

Prior approval for a larger home extension lets you build a single storey rear extension up to 8 metres deep on a detached house, or 6 metres on any other house, without a full planning application. You tell the council, the council tells your neighbours, and if nobody objects, or the council decides the impact on neighbours is acceptable, you can build. You cannot start until the council confirms or 42 days pass without a decision.

This guide explains how the process works in England, what it costs, what it does not cover, and how to decide whether it is the right route for your extension.

What is prior approval for a larger home extension?

Most houses have permitted development rights, which let you extend without planning permission within set limits. For a single storey rear extension, the standard limit is 4 metres beyond the rear wall of the original house for a detached house and 3 metres for any other house.

The larger home extension route raises those limits to 8 metres for a detached house and 6 metres for any other house. Government guidance describes it as a neighbour consultation scheme. The extension must still be single storey and no more than 4 metres high. In exchange for the extra depth, you must apply to the council for prior approval before you build, and your neighbours get the chance to object.

If you are not sure which permitted development limits apply to your project, our guide to what you can build without planning permission covers the wider rules.

Who can use it?

The larger limits only apply to houses. They do not apply if your house is:

on Article 2(3) land, which includes conservation areas, National Parks and Areas of Outstanding Natural Beauty
on a Site of Special Scientific Interest
in an area where a planning condition, an Article 4 Direction or another restriction has removed permitted development rights

Flats and maisonettes are not covered by these householder permitted development rules, so planning permission should be sought for an extension.

How the prior approval process works

You apply to the council. The application includes a written description of the extension (including how far it extends beyond the rear wall, its maximum height and its eaves height), a plan of the site, the addresses of any adjoining premises, your contact address, your email address if you are happy to receive notices by email, and the fee.
The council notifies your neighbours. The council, not you, sends notice to the owners or occupiers of adjoining premises. The notice gives a date for comments that is at least 21 days from the date of the notice, and public holidays are not counted.
The council decides. If no adjoining owner or occupier objects, the council's prior approval is not required. If one does object, the council must consider the impact of the extension on the amenity of the adjoining premises before deciding.
You wait for the outcome or the 42 day deadline. Work must not begin until the council tells you prior approval is not required, gives prior approval, or 42 days pass without a decision.

Once you have the go-ahead, the extension must be built in line with the details you submitted, unless you and the council agree otherwise in writing. The current rules set no deadline for completing the work.

How long does prior approval take?

The council has 42 days to decide. If it does not decide within that time, you can start work. That is shorter than the standard 8 week time limit for deciding most planning applications.

What happens if a neighbour objects?

An objection does not mean refusal. It means the council must assess the extension's impact on the amenity of the neighbouring property and decide whether that impact is acceptable. If prior approval is refused, the extension cannot go ahead at that depth under this route. The alternatives are an extension within the standard 3 or 4 metre limits, or a householder planning application.

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How much does prior approval cost?

The council fee for prior approval for a larger home extension is £249 under the fee schedule in force in England from 1 April 2026. For comparison, a householder planning application for an extension to a single house costs £548, and a lawful development certificate for a proposed extension costs half the normal planning fee.

You will also need a plan of the site and the measurements set out in the written description. Our guide to block plans and site location plans explains what the council expects. For build costs, see our single storey extension cost guide.

What prior approval does not cover

Prior approval only deals with the impact on neighbours. Your extension still has to meet every other permitted development rule. Two are worth checking early:

Materials. The exterior materials must be similar in appearance to those of the existing house. Similar does not mean identical, but a finish that does not meet this condition takes the extension outside permitted development.
Removed rights. If a planning condition, an Article 4 Direction or another restriction has removed permitted development rights for your house, the prior approval route is not available.

If your extension is within the standard 3 or 4 metre limits, you do not need prior approval at all. In that case a lawful development certificate can confirm the extension is lawful before you build.

How we decide which route fits

When a homeowner asks us about a rear extension, the depth decides the route, so we confirm the details before recommending anything. We ask for photos of the back of the house, a wider shot of the garden showing the boundaries and the neighbours either side, how far out from the back wall they want to go, and whether the house is detached, semi-detached or terraced.

On newer estates, we also check whether the original permission for the estate removed permitted development rights. If it did, a householder application is needed instead. The planned finish matters too: timber cladding on a brick house, for example, can fail the similar appearance test, so we talk through the outside finish early.

As a rough guide:

Within 3 metres (semi-detached or terraced) or 4 metres (detached): standard permitted development, ideally confirmed with a lawful development certificate.
Between those limits and 6 or 8 metres: prior approval for a larger home extension, if your house is not on designated land and still has its permitted development rights.
Beyond the standard limits on designated land, beyond 6 or 8 metres, over 4 metres high, or where permitted development rights have been removed: a householder planning application.

Frequently asked questions

Can I build a 6 metre extension without planning permission?

On a semi-detached or terraced house, yes, through prior approval, as long as the house is not on designated land, its permitted development rights are intact, and the extension is single storey and no more than 4 metres high. On a detached house the limit is 8 metres.

Do I need to tell my neighbours myself?

No. The council notifies the owners or occupiers of adjoining premises. Talking to your neighbours before you apply may still help, as an objection means the council must assess the impact on their property.

Is prior approval the same as planning permission?

No. It is a narrower process that only looks at the impact on the amenity of adjoining premises. The extension still has to meet all the other permitted development rules.

Next steps

If you are planning a deeper rear extension and want to know which route fits your house, we are happy to talk it through. Book a free advice call and we will look at your plans with you.