Published · By Brixter Construction
A rear extension is one of the most common ways to add space without moving house. Whether you need planning permission depends on the size of the extension, the type of house, and where you live. This guide covers the basics for homeowners in Hassocks, Burgess Hill, Haywards Heath, Hurstpierpoint and Ditchling, Cuckfield, Lindfield and nearby.
General guidance only, based on the rules for houses in England. Always check with your local planning authority before work starts — rules and designations can change, and every plot is different.
The short answer
Many single-storey rear extensions on houses can be built under permitted development (PD) rights, without a full planning application, if they stay within national size and design limits. Larger single-storey rear extensions may still avoid a full application by using the prior approval / neighbour consultation route. Multi-storey rear extensions, flats, and homes where PD rights have been removed usually need planning permission.
Mid Sussex District Council points homeowners to the Planning Portal for the detailed PD rules, and can confirm what applies to your property through a Lawful Development Certificate or informal officer advice.
Standard permitted development limits for rear extensions
According to the Planning Portal, these householder PD rights apply to houses only — not flats or maisonettes, and not in every case to houses created by conversion under certain PD classes. They also do not apply where a planning condition or an Article 4 Direction has removed or limited them.
For all extensions under PD, the main shared rules include:
- the extension must not take up more than half the land around the original house
- it must not be higher than the existing roof or eaves
- eaves height is limited to 3 metres if the extension is within 2 metres of a boundary
- it must not sit forward of the principal elevation
- materials should be of similar appearance to the existing house
- verandas, balconies and raised platforms are not permitted (a Juliet balcony is usually treated differently under government guidance)
For a single-storey rear extension under standard PD:
- detached houses: up to 4 metres beyond the rear wall of the original house
- other houses (semi-detached, terraced): up to 3 metres
- maximum height 4 metres
For a multi-storey rear extension under PD:
- up to 3 metres beyond the rear wall of the original house
- at least 7 metres from the opposite rear boundary
- roof pitch should match the existing house as far as practicable
- upper-floor side windows should be obscure-glazed and non-opening below 1.7 metres
- all multi-storey side extensions need planning permission
- on Article 2(3) designated land, all multi-storey rear extensions need planning permission
Side extensions under PD are single storey, max 4 metres high, and no more than half the width of the original house. On Article 2(3) land, all side extensions need permission.
Larger single-storey rear extensions (prior approval)
Where the larger home extension scheme applies, a single-storey rear extension can go further — up to 8 metres on a detached house, or 6 metres on other houses — if you notify the local planning authority and go through prior approval / neighbour consultation. That route is not available on Article 2(3) designated land or Sites of Special Scientific Interest. Details are on the Planning Portal’s prior-approval page for extensions.
When the rules are different in Mid Sussex
Original house means the house as it was first built, or as it stood on 1 July 1948 if it is older. Previous extensions already count against the PD limits.
Article 2(3) designated land includes conservation areas, Areas of Outstanding Natural Beauty / National Landscapes, National Parks, the Broads and World Heritage Sites. On that land, the larger 6 m / 8 m prior-approval scheme does not apply, and other PD limits tighten (for example all side extensions, and all multi-storey rear extensions, need permission).
In Mid Sussex, Article 4 Directions remove many domestic PD rights in places such as the Cuckfield and Lindfield conservation areas. Mid Sussex publishes an Article 4 list — check that list and your property’s planning history before assuming PD still applies.
South Downs National Park: National Parks are Article 2(3) and 2(4) land. The larger home extension PD scheme does not apply inside the Park, and side / multi-storey / cladding restrictions match other designated land. Hassocks borders the Downs; Ditchling and parts near Keymer and Clayton may be inside or next to the Park. If your plot is inside the Park, the South Downs National Park Authority is the planning authority — check before you design.
Flats, maisonettes, listed buildings and homes with planning conditions that remove PD rights all need a different approach. When in doubt, ask Mid Sussex (or SDNPA) before you start.
Building Regulations and the Party Wall Act
Even when planning permission is not needed, Building Regulations approval is usually still required for an extension. Planning and building control are separate processes.
If the work is near a shared wall or boundary, the Party Wall etc. Act 1996 may also apply. That is separate from planning. See the government’s Party Wall booklet for an overview, and take advice if neighbours’ foundations or a party wall could be affected.
Useful links
- Planning Portal: Extensions — planning permission
- Planning Portal: Extensions — prior approval
- GOV.UK: Permitted development rights for householders — technical guidance
- Mid Sussex District Council: Do I need planning permission?
- South Downs National Park Authority: Permitted development
- GOV.UK: Party Wall etc. Act 1996 — explanatory booklet
Thinking about a rear extension?
Brixter Construction builds house extensions across Mid Sussex from our base on Keymer Road in Hassocks — including rear and side extensions in Hassocks, Burgess Hill, Haywards Heath and Lewes. See our extensions page, or call Josh on 07518 403458 (Mon–Fri, 7:30am–6pm). You can also send us your details through our contact form. Quotes are free and without obligation.