Your Guide to Building a Single-Storey Extension: Key Rules You Need to Know.

Thinking about adding a single-storey extension to your home? Great news! Many of these projects fall under "permitted development," meaning you don’t need formal planning permission—so long as you stick to a few important rules and conditions. 

Here’s a simple, step-by-step guide to help you understand what’s allowed.

1. Restrictions on Designated Land.

If your house is on designated land (like conservation areas or national parks):- You can’t add any cladding to the exterior.- Side extensions aren’t allowed.- Rear extensions with more than one storey are not permitted.- The rules for larger rear extensions don’t apply here.

2. Keep Additions Under 50% of your land.

Your extension (plus any other outbuildings like sheds) can’t cover more than 50% of the land surrounding your original house. Make sure you include everything when calculating this!

3. No Extensions in Front of the House.

You can’t build an extension that extends past the front (or side if facing a road) of your house.

4. Materials Must Match.

Any new extension should use materials that are similar to the existing house. This ensures the extension blends in with the original structure. The only exception? Conservatories—these have more flexibility with materials.

5. Side Extensions Must Be Small.

If you're planning a side extension:- It must be single-storey.- It can’t be wider than half the width of the original house.

6. Height Restrictions for Side Extensions.

Side extensions must also follow height rules:- The maximum height is 4m.- If you're extending within 2m of your property’s boundary, the eaves can’t be higher than 3m.

7. Rear Extension Size Limits.

For single-storey rear extensions:- Detached homes can extend up to 4m from the rear wall of the original house.- Other homes can extend up to 3m.
If your house isn’t on designated land or a protected site:- Detached homes can extend up to 8m.- Other homes can extend up to 6m.

8. Maximum Height for Rear Extensions.

The highest point of your single-storey rear extension can’t exceed 4m.

9. Roof Height Limits.

Finally, the eaves and ridge of your extension can’t be taller than the existing house.

This quick guide should help you understand whether your project falls under permitted development. For more complex extensions, like two-storey builds, check out our other guides!

If you require additional information or would like to book a free quotation please contact us @ www.kenthouseextension.co.uk.