How Big Can A House Extension Be, Depending On My Property Type?

Thinking about expanding your home is an exciting prospect. An extension offers a way to create the extra space you and your family need without the upheaval of moving. However, one of the first questions that comes to mind for many people is, "How big can a house extension be?" The answer rests on several factors, including your property type and local planning rules. We understand that navigating these regulations can feel complex, so we've put together this short guide to help you understand the possibilities available for your home.

Understanding Your ‘Permitted Development Rights’

Before we go into specifics, it's helpful to understand 'Permitted Development Rights'. These are government-granted rights that allow homeowners to make certain changes to their property, including extensions, without needing to apply for full planning permission from their Local Authority. However, there are strict rules and limits to Permitted Development. Knowing these can help you understand the potential scope of your project from the outset.

Extension Sizes For Attached Properties

If you live in a semi-detached, terraced, or another type of attached home, the rules are quite specific. For these properties, your extension cannot extend more than 3 metres beyond the rear wall of the original house. This regulation is in place to ensure that your extension does not negatively impact your neighbours' light or privacy. We can work with you to design a space that maximises this 3-metre allowance, creating a functional and beautiful addition that respects the guidelines and enhances your home.

Extension Sizes For Detached Properties

Detached properties often have more flexibility when it comes to extensions. Under standard Permitted Development Rights, you can extend up to 4 metres from the rear wall. There is also a scheme known as the Larger Home Extension Scheme. This allows even bigger single-storey rear extensions of up to 8 metres. To proceed under this scheme, however, you will need to go through a prior approval process. This involves notifying your local council, which will then consult with your neighbours. We can guide you through every step of this process, managing the paperwork and communication to ensure everything is handled correctly.

Rules For Single-Storey Extensions

Single-storey extensions are a popular choice for creating open-plan living areas, like a new kitchen or family room. When planning one, there are several key rules to keep in mind:

• Height limit: the extension cannot be higher than 4 metres.
• Width restriction: it must not be wider than half the width of the original house. This helps maintain the property's original character.
• Material matching: the materials used for the exterior of the extension should be similar in appearance to those of the existing house. This creates a seamless and visually appealing finish.
• Rear extension limits: as mentioned, the extension cannot project beyond the rear wall by more than 4 metres for a detached house, or 3 metres for any other type of house.

We tailor our designs to meet these specific requirements while fulfilling your unique needs. We believe in creating a space that feels like it was always part of your home.

What About Two-Storey Extensions?

A two-storey extension can dramatically increase your living space, perhaps adding a new bedroom and expanding a downstairs living area. The rules for these are more stringent, however, and they often fall outside of Permitted Development Rights, meaning that a full planning permission application is usually required.

Here are the key considerations for a two-storey house extension in the UK:

• Rear projection: the extension cannot go past the back wall of the original house by more than 3 metres.
• Boundary proximity: the extension must be at least 7 metres away from the rear boundary of your property.
• Height near boundaries: if your extension is within 2 metres of a boundary, the maximum height at the eaves (where the wall meets the roof) must not be more than 3 metres.
• Roof pitch: the pitch of the extension's roof should match that of the original house as closely as possible to maintain a consistent aesthetic.

Embarking on a two-storey extension is a significant project, and our collaborative approach ensures we are with you at every stage, from initial design to navigating the planning process.

Prior Approval For Larger Extensions

For detached properties, you can often build a larger single-storey rear extension that extends between four and eight metres beyond the original rear wall of the house. This process falls under what is known as Prior Approval, and it is required to ensure that the extension does not cause unacceptable harm to the amenity of any neighbouring properties. The process involves submitting an application to your Local Authority that includes a written description of the proposed work and a site plan. The Local Authority will then notify your adjoining neighbours of the proposed development. If your neighbour raises an objection, the Local Authority will then take into account the impacts on their amenity before reaching a decision. If you do not hear from your Local Authority within the statutory 42-day period, the development is considered permitted.

Let's Plan Your Perfect Space Together

Understanding the house extension size limit is a crucial part of the planning process. Whether you have an attached or detached property, and whether you're considering a single or two-storey addition, these guidelines shape what's possible. At Nu Concepts, we specialise in bespoke residential architecture services that are tailored to your needs and compliant with all regulations. 

Are you ready to explore the full potential of your home? Let's start the conversation.

Book a discovery call with us today, and we can begin the journey of creating your ideal living space together.