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What Size Extension Can I Build Without Planning Permission in the UK?
Thinking about extending your home but not sure if you need planning permission? The good news is that many extensions can be built under Permitted Development Rights, meaning you can avoid a lengthy planning process if your design stays within certain limits.
General Rules for Extensions Without Planning Permission
Under Permitted Development, you can usually build an extension if it meets the following criteria:
Single-storey rear extensions
- Up to 3 metres deep for terraced and semi-detached houses.
- Up to 4 metres deep for detached houses.
- Under the Neighbour Consultation Scheme, this can be extended to 6 metres (terraced/semi)
- or 8 metres (detached)
Height Rules
- The extension must not be taller than your existing roof.
- If within 2 metres of a boundary, the eaves must not exceed 3 metres.
Overall limits
- The extension must not cover more than half the garden/land around the
“original house” (as it was first built, or as it stood on 1st July 1948). - Materials should be similar in appearance to the existing property
- Listed buildings, conservation areas, and other designated land usually have stricter rules.
Double-Storey Extensions
Permitted Development also allows some two-storey rear extensions, as long as:
- They don’t extend more than 3 metres beyond the rear wall of the original house.
- They’re no closer than 7 metres to the rear boundary.
- Loft Conversions
While not technically an “extension,” loft conversions often fall under Permitted Development too, provided they stay within volume limits and do not alter the roof shape excessively.
Important Exceptions
Planning permission is usually required if:
- Your property is a listed building.
- You live in a conservation area or other designated land (e.g., National Parks, Areas of Outstanding Natural Beauty).
- You want a side extension that’s more than one storey or more than half the width of the house.
Don’t Forget the Details
Every home is different, so it’s always a good idea to double-check with your local planning authority. Getting professional drawings also ensures your extension makes the most of the available space while staying within the rules.
👉 Need expert help? Our team specialises in planning and building regulation drawings, giving you peace of mind before you start building.
FAQs: Extending Without Planning Permission
How far can I extend my semi-detached house without permission?
Up to 3 metres under Permitted Development, or up to 6 metres with neighbour consultation.
How far can I extend my detached house without permission?
Up to 4 metres, or up to 8 metres with neighbour consultation.
Can I extend to the side without planning permission?
Yes, but the side extension must be single-storey, no more than 4 metres high, and no wider than half the width of the original house.
Do Building Regulations still apply if I don’t need planning permission?
Yes — Building Regulations approval is always required for extensions to ensure they are safe and compliant
Get in Touch with Al-Haitham
At Al-Haitham, we are dedicated to transforming your visions into reality as we specialise in architectural design and home building. Whether you are considering a home extension, a custom build, or simply need expert advice, we are here to assist you every step of the way. Get in touch with us to start planning your home extension or to discuss any architectural inquiries you may have. Our contact form is quick and straightforward, making it effortless for you to reach out for consultations, quotes, or to gather more information about our professional architectural services. We value open communication, so do not hesitate to connect with us. Our experienced team is eager to help turn your ideas into stunning architectural designs that meet your needs.