Building a Single-Story Extension in the UK Do You Need Planning Permission?

Share this article

Adding a single-story extension to your home is a fantastic way to gain valuable extra space. However, navigating the world of building regulations and planning permission can be daunting. One of the key questions you’ll face is whether you’ll need to go through the formal planning permission process.

The good news is that for many single-story house extensions, planning permission isn’t required. This is thanks to a set of rules called Permitted Development (PD) rights.

Video Source

These rights allow certain building works to be carried out without the need for a full planning application.

Understanding Permitted Development Rights

Permitted development rights apply differently depending on the type of property and the location. It’s important to check the specifics for your situation, but here’s a breakdown of the key points to consider for single-story extensions:

  • Location: PD rights may not apply in certain designated areas, such as conservation areas, Areas of Outstanding Natural Beauty (AONBs), or national parks. Additionally, some newer housing estates may have restrictions imposed on PD rights as part of the original planning permission.
  • Size and Scale: There are limitations on the size and scale of extensions permitted under PD rights.
  • Depth: For rear extensions, the maximum depth is typically 3 meters for terraced or semi-detached houses and 4 meters for detached houses.
    Height: The maximum height of the extension is generally 4 meters. However, there may be restrictions near boundaries, where the eaves (the lowest part of the roof) may need to be lower.
  • Position: Extensions cannot be built forward of the principal elevation, which is usually the front facade of your house. There are limited exceptions, such as small porches.
  • Materials: The materials used for the extension should be similar in appearance to the existing house.
  • Previous Extensions: Be aware that your house may have already used up some of its permitted development rights for previous extensions.

Planning Permission vs. Certificate of Lawfulness

While PD rights can be a great way to streamline the extension process, it’s important to be sure your project falls within the permitted development guidelines. One way to achieve peace of mind is to apply for a “Certificate of Lawfulness.” This is a formal request for your local authority to confirm that your planned extension complies with PD rights.

While obtaining a Certificate of Lawfulness may seem like an unnecessary step, it offers several advantages:

  • Confirmation: It provides you with written confirmation from the local authority that your extension is permitted development.
  • Peace of Mind: This can be invaluable during construction and when selling your property later.
  • Reduced Risk: If your extension is found not to comply with PD rights after construction, you may be required to make changes or even remove the extension entirely. A Certificate of Lawfulness helps mitigate this risk.

Going Beyond Permitted Development

If your desired extension doesn’t meet the PD criteria, all is not lost. You can still apply for formal planning permission. The planning process typically involves submitting detailed plans and drawings of your proposed extension, along with a fee. Your local authority will then consider your application and make a decision based on various factors, including the impact on the surrounding area and compliance with building regulations.

Building Regulations

It’s important to remember that even if your extension falls within permitted development rights, you’ll still need to comply with building regulations. These regulations ensure that your extension is structurally sound, meets fire safety standards, and provides adequate ventilation and energy efficiency. Building regulations are separate from planning permission and are enforced by your local authority building control department.

Key Considerations Before You Begin

Before embarking on your single-story extension project, here are some additional points to consider:

  • Planning Consultant: While not essential, a planning consultant can be a valuable resource, particularly for navigating complex projects or those in sensitive locations. They can advise on PD rights, planning applications, and building regulations.
  • Party Wall Agreements: If your extension is built near a boundary with your neighbor, you may need to enter into a party wall agreement. This is a legal agreement that outlines the rights and responsibilities of both parties during construction.
  • Building Costs: Getting quotes from reputable builders is crucial for budgeting your project realistically. Factor in not just the build cost but also the potential expenses for architectural plans, building control fees, and any necessary party wall agreements.


Building a single-story extension can be a fantastic way to enhance your living space. By understanding permitted development rights, the planning permission process, and building regulations, you can navigate the project with more confidence. Remember, seeking professional advice from a planning consultant or architect can be invaluable


Share this article
Scroll to Top