Many homeowners can add a sizeable extension without applying for full planning permission, thanks to permitted development rights. Knowing the limits before you design anything can save months of waiting and hundreds of pounds in fees.
This guide covers the main permitted development rules for houses in England, and what that means for your project in Sussex.
Planning an extension? We offer a free site visit to look at what your home can take and give you a written estimate. Request a free quote or call 07771 393494.
The short answer
| Extension type | Detached house | Semi-detached or terraced house |
|---|---|---|
| Single storey rear | Up to 4m deep | Up to 3m deep |
| Single storey rear (prior approval route) | Up to 8m deep | Up to 6m deep |
| Two storey rear | Up to 3m deep | Up to 3m deep |
| Single storey side | Up to half the width of the original house | Up to half the width of the original house |
| Maximum height (single storey) | 4m | 4m |
All depths are measured from the rear wall of the original house, meaning the house as it was first built or as it stood on 1 July 1948. If a previous owner has already extended, that allowance may already be used up.
Single storey rear extensions
This is the most popular type of extension and the one most likely to fall within permitted development. The main conditions are:
- No deeper than 3m on an attached house or 4m on a detached house
- No higher than 4m overall
- Eaves no higher than 3m if the extension is within 2m of a boundary
- Eaves and ridge no higher than those of the existing house
- Materials similar in appearance to the existing house
That 3m to 4m allowance is often enough for a good-sized kitchen diner. Our house extensions page shows the kind of work we build within these limits.
Going bigger with prior approval
Under the larger home extension scheme, you can build a single storey rear extension up to 6m deep on an attached house or 8m on a detached house. You do not need full planning permission, but you must notify your council first. Your neighbours are told and can object, and the council then decides whether the impact on them is acceptable.
The process usually takes around eight weeks and is cheaper than a full planning application.
Side extensions
A single storey side extension can be built under permitted development if it is no more than 4m high and no wider than half the width of the original house. Side extensions are not permitted development in conservation areas, which matters in parts of Lewes, Battle and Tunbridge Wells.
Two storey extensions
A two storey rear extension can extend up to 3m from the original rear wall, as long as it is at least 7m from the rear boundary. Upper floor windows on the side must be obscure glazed and non-opening below 1.7m. Two storey side extensions always need planning permission.
Not sure what your home allows? We have built extensions across East and West Sussex for over 20 years and can tell you on site what is realistic. Book a free site visit or call 07771 393494.
Porches
A front porch is permitted development if its ground floor area is no more than 3m², it is no taller than 3m and it sits at least 2m from any boundary next to a road. Our guide to brick porches covers this in more detail.
When you will always need planning permission
- Your home is a listed building
- You live in a conservation area, National Park or Area of Outstanding Natural Beauty (now called National Landscapes), which covers much of the High Weald and South Downs
- The extension would face a road from the principal elevation
- The extension and other outbuildings would cover more than half the land around the original house
- Your permitted development rights have been removed by a planning condition, which is common on newer estates
- You live in a flat or maisonette, which has no householder permitted development rights
Permitted development is not the same as Building Regulations
Even if you do not need planning permission, your extension must still meet Building Regulations for foundations, structure, insulation, drainage and fire safety. You may also need a Party Wall Agreement if you are building on or near a shared boundary. We work to Building Control on every extension we build, from the foundations up.
Get a Lawful Development Certificate
A Lawful Development Certificate from your council confirms that your extension is permitted development. It is not compulsory, but it gives you written proof when you come to sell, and many mortgage lenders and buyers’ solicitors will ask for it. The application fee is half the cost of a householder planning application.
Check before you build
Rules can change, and councils interpret them differently. Before you commit, check the Planning Portal or speak to your local planning team at Wealden, Lewes, Mid Sussex, Rother, Brighton and Hove, Eastbourne or Tunbridge Wells.
Ready to plan your extension?
Bradford Brickwork builds single storey and two storey extensions across East and West Sussex, from groundworks and foundations to the roof. Every project starts with a free site visit and a detailed written estimate, and we are rated 9.77/10 on Checkatrade.
Get your free quote or call 07771 393494.
FAQs
How big can a single storey extension be without planning permission? Up to 3m deep on a semi-detached or terraced house, or 4m on a detached house, and no more than 4m high. Prior approval can extend this to 6m and 8m.
Can I build a kitchen extension without planning permission? In many cases, yes, as long as it stays within permitted development limits and your home is not in a conservation area or listed.
Do I need to tell my neighbours? Not for standard permitted development, but you must under the prior approval route, and you may need to serve Party Wall notices.
Can I extend a house that has already been extended? Possibly, but the limits apply to the original house, so earlier extensions count towards your allowance.
