Expanding your home is probably one of the most popular ways of gaining space, comfort, and value without all the trouble of relocation. An extension can provide more space in a kitchen or a bedroom, or simply more space to relax in. The possibilities for extensions are endless. But first thing’s first, before you begin a takedown of the barriers and a pour of the concrete, it would serve you well to get to grips with exactly how big an extension you are able to build in the UK without planning permission. This is where permitted development rights come in and quite surprisingly homeowners enjoy that much of a flexibility, as long as certain rules are followed.

What Size House Extension Can You Build Without Planning Permission in the UK?

The good news is that homeowners can easily get planning permission for a good sized extension in the UK because many are allowed under the permitted development rules. These rules will make it easier to improve your home whilst ensuring that neighbourhoods are consistent and overdevelopment is avoided.

Therefore, what extension size can you construct without having planning approval? To extend a detached house into a single storey rear extension, you are only allowed to make such extension as long as 8 metres in depth. For semi detached and terraced houses the limit is 6 metres. These allowances are permanent from 2020 and apply provided your project is in accordance with other regulations in height, proximity to boundaries and design.

For multi-storey extensions or those that fall outwith these measurements; you will almost definitely need to make a planning application. But within these boundaries, you can acquire a significant new space at home without even a visit to the planning office.

Understanding Permitted Development Rights for Homeowners

Permitted development rights are a county-specific set of rules that specify the type of improvements which may be made to a home without the need for formal planning permission as long as that improvement meets certain requirements. Many of these rights are automatically bestowed upon many residential properties, although exceptions do exist.

For example, if you live in a listed building, in a conservation area or in a flat or maisonette, your permitted development rights may be curtailed or removed altogether. For such cases you will need to seek full planning permission for nearly all external work.

Even where permitted development rights apply, compliance with specific measurements, design standards and constraints is essential. These therefore include maximum size of the extension, distance from the property boundaries, overall height, and use of similar materials in appearance to that of the existing property.

Before doing the work, it’s always sensible to lodge an application for a Lawful Development Certificate with your local council. This certificate ensures that your proposed extension you want done is in permitted development rules, and this will protect you from any future legal arguments or issues if you sell your home at some point.

Rear Extension Limits for Semi-Detached Properties

If you are asking what size extension can I build without planning permission particularly for a semi-detached property, then the rules are not too complicated. You can add up to 6 metres in depth to the back of your property without full planning approval provided it doesn’t extend more than half the original width of the house.

However, if you wish to build something bigger than it, or if your intended extension may negate the light and privacy of your neighbours, it may be the cause to trigger the need for full planning. In other instances your neighbours may also be consulted under what is known as the Neighbour Consultation Scheme if your extension is close to the maximum allowed development limits.

Height and Width Rules for Extensions Without Permission

Other than depth limits, you need to follow specific height and width rules to stay within permitted development rights. For single-storey extensions, no more than 4 metres high may be constructed. Where your eaves extend within 2 metres of a boundary the maximum height to which the eaves can extend is 3 metres unless you wish to over shadow the neighbours property.

For two-storey extensions (which are much more restricted under permitted development), the height cannot exceed your existing roof and the rear wall cannot extend beyond 3metres from the original building.

It is also worth remembering that all the extensions may not exceed 50% of the total area around the original house. This involves previous extensions of our buildings such as sheds or garages, so if, for instance, you have already pressed on a lot of your outdoor space then you are likely to be less likely to have room to extend without applying for planning permission.

Side and Wrap-Around Extensions: What’s Allowed?

Side extensions are a great way of creating much appreciated internal rooms in the houses, where they have unused access from the side or plots are wider. Under permitted development you can build a single storey side extension not exceeding 3 metres in width and not over 4 metres tall.

But if you’re looking at a wrap-around extension (a combination of side and rear extensions), then you are stepping outside of PD rights. As wrap-around extensions tend to change the shape and footprint of a house drastically, they almost always need the full planning permission.

Additionally, design also determines whether or not your extension is in the category of the permitted development. The extension must be built from materials resembling the original house, their colour and type, and the roof pitch should also resemble the apex of the existing roof. These rules will ensure the character of the property and its surroundings does not suffer in its entirety.

When Does an Extension Require Full Planning Approval?

Although the permitted development rights remain a very permissive tool, there are still many situations, where full planning approval is mandatory. These include:

• If your property is a listed building.
• When your proposed extension exceeds the permitted development size limits.
• If the extension changes the use of your property or includes a balcony.

In such cases, you’ll have to provide detailed plans to your local planning authority, and go through the entire application process. While this can be intimidating, however there is also a chance to design a more ambitious or customised extension which can really enrich your life.