Planning Consultant - Chris Scott
Hi, I’m Chris,
I hold anĀ MA in Planning and work as a Planning Consultant

So you’ve decided you need to add more space to your home. In most cases, it’s the rear of the property where there is available space to expand. Therefore, the first question many people have is “do you need planning permission for a rear extension?” The answer will depend on several variables which include:

  • Are you looking for a single or two storey rear extension?
  • Has the rear of the property been previously extended?
  • Does the property still hold Permitted Development Rights?
  • Is the property located in a National Park, Conservation Area or similar?

I’ll discuss rear extensions to dwellings under various scenarios to provide an indication if planning permission may be required. A rear extension on a dwelling may come under permitted development rights. If not the proposal will need to be submitted as a householder planning application.

Single or Two Storey Rear Extension?

I think the most logical place to start is whether you are considering a single or two storey rear extension. If you are planning either a single or two storey rear extension there is a possibility it can come under permitted development rules (PD). That is provided that the size of the rear extension complies with the PD rules. Furthermore, it needs to be determined if the property can benefit from PD rules. In some cases, PD rights have been removed from a property.

Single Storey Rear Extension
A conservatory is a typical example of a rear extension that can often be completed without a planning application – Image: premierwindowsoswestry.co.uk

It is also possible in some cases to construct a two storey rear extension without planning permission under PD rules. However, the PD rules for two storey rear extensions are far more limited than that of single-storey rear extensions.

General PD Rear Extension Criteria

I’ve now written several posts on permitted development rules. Therefore, I’m not going to repeat myself too much with this post. I want to keep this post focused on when planning permission may be required for rear extensions. If you click the links within the information below you will be able to find out more about PD rules. The general PD rules which apply to all rear extensions are:

Single Storey Rear Extensions under PD Rules

The permitted development rules around single-storey rear extensions are by far the most generous. Before 2013 the largest single storey rear extensions allowed under PD was 3-4m. However, in 2013 a new rule was introduced called the larger home extension scheme. That allowed rear extensions under PD up to 6m for semi-detached properties and up to 8m for detached properties. That right was set to end in 2019, however, it has now been made a permanent right.

Larger Home Rear Extension
The larger home scheme under PD rights means it can be possible to construct an 8m single-storey rear extension on a detached dwelling – Image: homeandbuild.co.uk

Therefore without planning permission under PD rules, it is possible to construct significant rear single-storey extensions. This could typically include a conservatory. You do have to submit a prior approval application to your local council or a larger home rear extension. There are also specific rules for single-storey rear extensions under PD:

  • Single storey rear extension max height of 4m.
  • Eaves height of the rear extension must be no higher than the existing property.
  • Materials to be similar to existing property (conservatories are an exception to this rule.)
  • Larger home rear extensions are not allowed on Article 2 (3) land, which includes National Parks and Conservation Areas.

If you are planning a rear extension and it does not fall under these rules you will need planning permission.

Two Storey Rear Extensions under PD Rules

As stated previously, unfortunately, the PD rules for two storey rear extensions are not quite as generous. First, if your property is on Article 2 (3) land such as a National Park or a Conservation Area, unfortunately, you cannot construct a two-storey rear extension under PD rules. Therefore, if your property is located on Article 2(3) land, you will need planning permission for a two-storey rear extension.

For other properties under PD rules, a two storey rear extension may be possible, but it can only project beyond the rear wall of the original dwelling by 3m. Again there are other PD rules to comply with:

  • Two storey rear extensions must not have an eave or ridge height above the existing property.
  • A two storey rear extension cannot be within 7m of the rear property boundary.
  • Upper floor side windows to be obscurely glazed.
  • Any upper floor opening must be at least 1.7m above the floor.

The additional PD restrictions on two-storey rear extensions such as the 7m rule are to protect neighbour amenity, such a loss of light and privacy. It’s important to note that to comply with PD, your rear extension must follow all of the rules. So for instance, you may be ok on the 50% development rule but your two storey rear extension is within 7m of the rear boundary, it cannot, therefore, come under PD rules.

Two Storey Rear Extension
A significant two storey rear extension such as this could not be completed under PD rules and would require permission under a householder planning application – Image: homebuilding.co.uk

How to confirm if a Rear Extension comes under PD?

With some proposals it’s pretty easy to work out if a rear extension can be constructed under PD rules, however, in other cases, it can get very, very complicated. These are the various steps you need to go through to confirm if your rear extension ideas can be completed under PD rights without the need for planning permission:

  1. Planning History Check: A planning search needs to be undertaken to see if any previous planning permissions have removed PD rights. Furthermore, the size of the curtilage and the size of the original building need to be understood.
  2. Lawful Development Certificate (LDC): If you are absolutely confident you can construct your rear extension under PD rules without planning permission a LDC is not strictly required. However, it does serve as a piece of mind that a planning enforcement officer is not going to come knocking telling you to demolish your new rear extension. An LDC can also help to sell your property in the future as evidence your extension was completed in line with PD rules.

LDC Appeals for Rear Extensions

Now, the local planning authority may refuse your LDC application stating the proposals do not conform to PD rules. In general, the decision will be correct and you would be directed to submit a householder planning application for your rear extension.

However, that’s not always the case. The planning officer may have not been aware of the full details of the properties planning history and size of the original dwelling or curtilage. If that’s the case a planning consultant such as myself can appeal against the refusal of the LDC to the Planning Inspectorate, also know as PINS. However, its best to get a planning consultant involved before the LDC certificate is determined, as providing that additional evidence before a determination may have turned that refusal into an approval, with no need to appeal.

Householder Planning Applications for Rear Extensions

So if your sure you rear extension ideas do not come under PD rules or your LDC certificate has been refused then a householder application will be required. However, that doesn’t mean the PD rights for your property are completely irrelevant. A smart planning consultant will be using applicable PD rules to demonstrate a ‘fallback’ position based on the available PD rights.

The ‘fallback’ position is what development you could carry out under PD rules if the householder planning application was refused. The applicable development that can be carried out to a property under PD rules is a ‘material consideration’ in the determination of a householder planning application. However, to effectively demonstrate the fallback position a prior notification (larger home extension) or lawful development certificate would likely be required as evidence.

What about Rear Extensions in the Green Belt?

As there are PD restrictions on rear extensions for properties located in National Parks and Conservation Areas, you would be forgiven for thinking there are similar restrictions on properties located in the Green Belt. However, for rear extensions under PD in the Green Belt, there are no additional rules or restrictions. You can even go for the single storey larger home rear extension up to 8m.

Green Belt Rear Extensions
PD rules still apply in the Green Belt for significant rear single storey extensions under the Larger Home Extension rights.

However, with a planning application, the rules around Green Belt development become more complicated. The applicable local plan may state what is a ‘reasonable’ increase for a rear extension in the Green Belt. Some local plans will actually state a percentage (typically 30%). Others just leave it up to the discretion of the planning officer.

When it comes to discussions over percentages, it’s very important that the size of the original dwelling is properly understood. For instance, if the property is older than July 1st 1948 then any previous rear extensions should be regarded as part of the original dwelling. Therefore, those rear extensions should not be included in the percentage increase calculations.

In some cases, Green Belt very special circumstances may need to be demonstrated. Part of those very special circumstances can include relevant permitted development rights, hence the ‘fallback’ position.

Do you need Planning Permission for a Rear Dormer Extension?

In many cases, a rear dormer extension can be added to a dwelling without planning permission under PD rules. However, as you would expect there are several conditions that need to be met:

  • A rear dormer extension cannot be higher than the existing ridgeline of the dwelling.
  • It must be set back from the eaves by 20cm.
  • Volume < 40m3 for a terraced dwelling.
  • Volume < 50m3 for semi/detached dwelling.

There are other conditions for rear dormer extensions completed under PD which can be read on the Planning Portal.

Conclusions on Rear Extensions and Planning Permission

Permitted development rights are a powerful tool for rear extensions, especially single-storey rear extensions. Therefore, it’s worth exploring if the size of the rear extension you require could be completed under PD rules. Even if you believe the rear extension you desire can be completed under PD, its best to secure a Lawful Development Certificate to make sure.

If the proposals cannot be completed under PD rules, these rights can help to demonstrate the proposals under a planning application are a reasonable form of development. Demonstrating lawful development under PD rules can help similar development just outside of the rules to appear less significant.

If you’re considering a rear extension and require some guidance around PD rules, submitting a lawful development certificate or householder planning application please get in touch.