You do not always need planning permission for a single-storey extension. Many extensions can be built under permitted development rights, provided they meet specific rules covering their size, height, position and design.
If you are thinking about extending your home, it is important to understand which rules apply to your property. The answer depends on the size and position of your proposed extension, the type of property you own and where it is located.
At Lifestyle Windows, we have more than 30 years of experience designing and installing home extensions across Derbyshire, Nottinghamshire and Leicestershire. We can also work with our architectural partners to help with the planning, design and structural side of your building project.
What is permitted development?
Permitted development rights allow certain home improvements to be carried out without a full planning application, provided they meet specific conditions.
For single-storey extensions, these rules are covered by Class A of the General Permitted Development Order. They set limits on factors such as the extension’s size, height, position and relationship to the original house.
Previous extensions can also affect what you are allowed to build, so it is important to establish what permitted development rights apply to your property before work begins.
If you’re considering adding more space to your home, our single-storey extensions page explains more about the types of extension we can design and install.
What counts as the original house?
When planning rules refer to the “original house”, they mean the dwelling as it was first built or, if it was built before 1 July 1948, as it stood on that date.
This matters because permitted development measurements are based on the original dwellinghouse, rather than necessarily the existing house as it looks today.
For example, a previous extension can affect how much additional development is possible. The total enlargement of the original house needs to be considered when working out what you can add.
If you are unsure about the history of your property, government technical guidance provides further detail on how these measurements are applied.
How far can a rear extension extend?
For a standard single-storey rear extension under permitted development, you can generally extend beyond the rear wall of the original house by:
- Up to 4 metres for a detached house
- Up to 3 metres for any other house, including a semi-detached or terraced house
These measurements are taken from the original rear wall rather than from a later extension.
A single-storey rear extension can also be up to 4 metres high. If it is within 2 metres of a boundary, its eaves height must not exceed 3 metres.
The roof design matters too, so the height and shape of the roof need to stay within the relevant permitted development restrictions.
Can you build a larger rear extension?
In some circumstances, yes. A larger single-storey rear extension can be possible through the neighbour consultation scheme, also known as the prior approval process.
The larger home extension provisions allow a rear extension to project:
- More than 4 metres and up to 8 metres for a detached house
- More than 3 metres and up to 6 metres for any other house
This route has additional requirements. You must notify your local planning authority, which will consult adjoining neighbours before deciding whether prior approval is required.
If you want to go beyond these limits, or your project does not meet the other permitted development conditions, you may need full planning permission.
What are the rules for a side extension?
Side extensions have their own permitted development requirements. A single-storey side extension can generally qualify where it:
- Is no more than 4 metres high
- Is no more than half the width of the original house
- Is only a single storey
The materials should also have a similar appearance to those used on the existing house, subject to the relevant rules.
The position of the extension’s side elevation can be important too. An extension that sits on the principal elevation may be subject to different planning considerations, so this should be established before relying on permitted development rights.
How much of your garden can an extension cover?
The overall footprint of your building project is another important consideration.
Under permitted development rules, extensions and other buildings must not cover more than 50% of the land around the original house. Previous extensions and outbuildings count towards this total.
This means the amount of garden available for a new extension is not the only consideration. What has already been built on the property can affect how much space remains available under permitted development.
Boundary distance also matters. Where an extension is within 2 metres of any boundary, the eaves height is restricted to 3 metres.
Considering the footprint, height and position together at the design stage can help avoid problems later. The design should also take into account practical issues such as natural light, privacy and the relationship with neighbouring properties.
What happens in a conservation area or other designated area?
Permitted development rights are more restricted on certain types of designated land. This includes conservation areas, National Parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites.
Sites of Special Scientific Interest can also have additional restrictions.
For example, side extensions are not permitted development under Class A on certain designated land, while the larger rear extension provisions do not apply on Article 2(3) designated land or SSSIs.
There can also be additional requirements for exterior work and materials. If your property is in a conservation area or another designated area, check the position with your local planning authority before starting work.
Listed buildings require particular care because planning permission and Listed Building Consent are separate matters. If your property is listed, establish which permissions and consents are required before carrying out exterior work or other alterations.
Do building regulations apply to a permitted development extension?
Yes. Planning permission and building regulations approval are separate.
An extension can fall within permitted development and therefore not require a planning application while still needing to comply with building regulations.
These regulations cover areas such as structural stability, fire safety, insulation, ventilation and drainage. Existing features, including a vent pipe or other services, may also need to be considered as part of the design.
If your project involves a shared wall, the Party Wall Act may also apply. This is separate from planning permission and building regulations, so meeting one set of requirements does not automatically satisfy the others.
Should you apply for a Lawful Development Certificate?
If you believe your extension qualifies as permitted development, you can apply to your local authority for a Lawful Development Certificate.
This is not the same as planning permission and is not compulsory, but it provides formal confirmation that a proposed or completed development is lawful.
It can also provide useful evidence if you sell your property in the future, particularly if a buyer or solicitor wants confirmation that the extension did not require full planning permission.
Getting the right advice before you start
Planning rules can become complicated when you factor in previous extensions, property boundaries, roof design and designated areas. Getting these details right before finalising your plans can save time and avoid costly changes later.
At Lifestyle Windows, we offer a comprehensive design and build service for home extensions across Derbyshire, Nottinghamshire and Leicestershire. We have partnered with ProDesign to provide planning, design and structural calculation services, with our team able to take measurements at your property and create technical drawings for your proposed extension.
We can also liaise with your local council and take care of building regulations and structural calculations as part of the service. This gives you one point of contact throughout your project, from the initial design through to completion.
Whether you want to create extra space at the back of the house, replace an existing conservatory or build a larger living area, we can help you explore the options available. You can also see examples of our previous work in our case studies.
Ready to start planning your extension?
Understanding the planning rules is a useful first step when considering a single-storey extension. While many projects can fall under permitted development, the rules depend on the individual property and proposed design.
Not sure whether your proposed extension needs planning permission? Our team can talk you through your options and help you understand the next steps, from initial design and planning through to installation.
Visit our showroom in Ilkeston to explore different extension styles and products, book an appointment with our team to discuss your ideas or request a free quote for your project.