Extending Your Home in the North Somerset Green Belt: 10 Things You Should Know

Planning an extension to your home in the North Somerset Green Belt can feel daunting. The area is protected for good reason—it helps to prevent urban sprawl and preserve the open, rural character of the landscape. But that doesn’t mean improvements to your home are off the table. With the right design and a solid understanding of the rules, extending in the Green Belt is achievable.

A contemporary extension to an existing house in the North Somerset Green Belt

Here are ten key things every homeowner should understand before moving forward:

1. The Green Belt Is Meant to Stay Open

The main purpose of the Green Belt is to keep the countryside open and free from overdevelopment. That means any new building—like an extension—is only allowed if it doesn’t harm that sense of openness. Large, bulky, or prominent extensions will usually be refused. Instead, any proposal should feel modest, well-proportioned, and sensitive to the surroundings.

2. Not All Extensions Are Considered Equal

Extensions are often treated as "inappropriate development" in planning terms—but there are exceptions. One of the main tests is whether the proposed addition is “disproportionate” in size compared to the original house. If it is, it’s unlikely to be supported. The goal is to avoid homes growing too large over time and gradually eroding the openness of the area.

3. What Counts as the “Original” House?

For planning purposes, the “original” building is usually defined as your house as it stood on 26 July 1985. If it was built after that date, then the starting point is its original size when first built. Any extensions added after that are counted towards the total increase in size—and that’s crucial when working out what’s considered proportionate.

4. The 50% Rule Is a Useful Guide

In North Somerset, a good rule of thumb is that extensions shouldn’t increase the original floor area by more than 50%. That includes previous extensions, loft conversions, and even unbuilt extensions that already have planning approval. If your home has already been extended close to this limit, you may find that further enlargement isn’t allowed.

5. Size Isn’t Everything—Form and Impact Matter Too

Even if your extension is under the 50% limit, it still needs to be designed carefully. Height, width, bulk, and where it sits on the site all affect how “open” the space feels. A tall or poorly placed extension can still be refused if it feels too dominant or harms the rural character of the setting. In short: being under the size limit isn’t a free pass.

6. Detached Garages and Outbuildings Count Too

You might be thinking of adding a garden room, garage, or studio instead. These are sometimes allowed in the Green Belt—but only if they are clearly secondary to the main house and don’t harm the open feel of the site. They should be small in scale, single storey, and well hidden from public view where possible.

7. Design Quality Is Critical

Good design matters more than ever in sensitive areas like the Green Belt. That means choosing materials that match or complement the existing house, using proportions and rooflines that feel natural, and keeping any new parts clearly subservient to the original building. Ideally, your extension should look like it belonged there from the start—or at least sit comfortably alongside it.

8. Think About Neighbours and Gaps Between Homes

Planning isn’t just about your own house. It's also about how the extension affects neighbours. Councils look carefully at light, privacy, and visual impact. Leaving gaps between buildings, setting extensions back from boundaries, and avoiding overbearing forms are all key ways to make your design more neighbour-friendly—and more likely to gain approval.

9. Talk to a Professional Early

Because Green Belt rules are complex, it’s wise to involve an architect or planning consultant early on. They can assess your property’s history, check what's been built already, and help shape a proposal that meets planning expectations. North Somerset Council also offers pre-application advice, which can help flag up any issues before you submit a formal application.

10. It’s Not Just About Planning Permission

Even if your extension gets the green light, it still needs to work for you. That means thinking beyond rules—considering how the space will be used, whether it improves the home’s energy efficiency, and how it connects to your garden or surroundings. A thoughtful, practical design will always add more long-term value than something simply squeezed within the rules.

Final Thoughts

Extending a home in the Green Belt isn’t about pushing boundaries—it’s about working within them, creatively and carefully. With a realistic brief, a considered design, and the right support, it’s absolutely possible to improve your home while protecting the landscape that makes North Somerset so special.

If you’re thinking about an extension in the Green Belt and want clear, honest advice from an architect who understands the area, feel free to get in touch.