Above: Extensions by architects on Design for Me. Click on the image to see their full profile and shortlist them for your project.
How big can you build an extension without planning?
The permitted development rules have recently been relaxed, allowing you to build an extension without planning permission of up to six metres (or eight metres if your house is detached).
Before you set to work, we’ve put together a checklist to make sure this applies to your project:
1. Will your extension be completed by May 2019?
This is the deadline to take advantage of the more generous allowance for extensions (see above).
Update 2020: Great news – the deadline no longer applies and the ‘lager home extension scheme’ has been made permanent!
2. Is your property a house?
Flats, maisonettes or any other type of buildings do not have permitted development rights, so you won’t be able to build your extension without full planning permission. Also, be aware that if your property has undergone a change of use or been converted into a house in the past, it may not enjoy permitted development rights.
3. Have you or any previous owners extended the house since 1948?
If so, these extensions will eat into your permitted development allowance.
4. Is your property listed or on ‘designated land?’
Or other ‘protected’ areas, including Conservation Areas, National Parks, areas of Outstanding Natural Beauty, the Norfolk or Suffolk Broads or a World Heritage Site? Your permitted development rights might even have been removed if there is an ‘Article 4’ direction for your property.
Hopefully, it may only be the case that your permitted development rights have been restricted on designated land, meaning you cannot:
- build more than one storey;
- build a side extension;
- or clad the exterior.
Still with us? Great! Now down to the nitty gritty…
Increased permitted development rules for an extension
The notes below are intended as a brief summary and should not be taken as design guidance. We strongly recommend you read the official guidance in full before proceeding (read it here):
Permitted development rules applicable to ALL extensions
- Materials to be similar to the existing house
- No verandas, balconies or raised platforms
- Must not be taller than the existing house
4. The extension(s) should not take up more than half of the garden/outdoor space
5. A single storey extension can’t be more than four metres high. If the extension is within two metres of the properties boundary, it can’t be more than three metres high.
Permitted development rules for front extensions
Not allowed under permitted development rules, but you can still apply for planning permission.
Permitted development rules for side extensions
- Must not front onto the road
- Single storey only
- Maximum of three metres out from the original house
- Must not be more than half the width of the original house
Permitted development rules for single-story rear extensions
1. Under the relaxed rules, you can extend up to eight metres for detached houses and six metres for all other houses. Please note that for these larger extensions (beyond four and three metres respectively) you will need to give notification under the Neighbour Consultation Scheme. If you get any objections, you may not be able to build a larger extension.
Permitted development rules for double-story rear extensions
- MAXIMUM HEIGHT: Firstly the eaves and pitch heights must be no higher than those of the existing house. However, if the building is within two metres of a boundary, the overall maximum eaves height is restricted to 3m. The roof pitch should match the existing house as much as reasonable practicable.
- FOOTPRINT: Under permitted development rules, you can extend up to three metres from the original house* but it must be more than seven metres from the rear boundary (opposite the rear wall). Any extensions to the original house*, sheds or outbuildings should not exceed more than 50% of the total area of land around the house.
- MATERIALS: The materials used should be similar in appearance to that of the existing house.
- LOCATION: Two storey extensions to the side or front of the original house are not permitted development.
- OTHER: No verandas, balconies would be allowed without planning permission. Any upper floor window in a side elevation must be obscured glazing and non-opening (unless its more than 1.7m from floor level internally).
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