Establish which elevation is the side
A wall beside a driveway is not necessarily a side elevation for planning purposes. Identify the principal elevation and the original building form first, particularly on corner plots or houses with several prominent frontages. An extension cannot project beyond a side elevation that fronts a highway under the ordinary Class A rights.
The original house is the building as it stood on 1 July 1948, or when first built if later. Previous extensions do not redefine that baseline. Historic drawings and the planning history help distinguish original walls from additions that must be included in the overall assessment.
Apply the width and single storey limits
An enlargement extending beyond an original side wall must be single storey, no more than 4 metres high and no wider than half the width of the original house. The width test concerns the enlargement, rather than simply the clear internal width of the room. Wall thickness and the extent of connected development matter.
Do not assume an existing side addition leaves a fresh half-width allowance for another project. Assess the total enlargement where additions join. Unusual layouts, including stepped walls and extensions on both sides, need careful interpretation using the diagrams in the government's householder technical guidance.
Resolve roof height and external appearance
Within 2 metres of a curtilage boundary, extension eaves must not exceed 3 metres. This operates alongside the 4 metre overall limit for a single storey side enlargement and the restrictions relating to the existing house's roof and eaves. Measure these separately rather than labelling a roof simply as low enough.
Materials used for exterior work generally need to resemble those of the existing house. A contrasting finish may therefore require a planning application even where the footprint appears compliant. Roof junctions, rainwater drainage and access for future maintenance also deserve attention before the proposed width is fixed.
Side return and wraparound extension plans
- Existing and proposed ground-floor layouts
- Roof junction and daylight drawings
- Coordinated structural opening information
Assess side and rear work together
A proposal that turns around the rear corner cannot be tested as two unrelated permitted development projects. Where the enlargement extends beyond both an original side wall and an original rear wall, the relevant side and rear limitations apply together. Depending on the geometry, the width assessment can catch more of the combined addition than expected.
It is nevertheless too broad to say that all wraparound extensions are automatically forbidden under permitted development. Some combined arrangements can meet the applicable tests; many familiar L-shaped designs cannot. Draw the original walls and the whole connected enlargement clearly, then assess the actual configuration with the local planning authority.
Check land restrictions and the planning route
On designated land, including conservation areas, National Parks and National Landscapes, an extension beyond an original side elevation is not permitted under these householder rights. Conditions or Article 4 directions may impose further restrictions elsewhere. Flats, maisonettes and certain converted houses also fall outside the normal householder entitlement.
Coverage matters too: extensions and other buildings cannot occupy more than half the curtilage excluding the original house footprint. Use side return and wraparound extension plans to examine the complete footprint, and our permitted development guide for related constraints. Where appropriate, certificate drawings can document a compliant proposal. If permission is needed, local design and neighbour amenity policies guide the application instead. Building regulations still require separate consideration with building control.
This guide is general information only and does not replace advice on your specific property. Rules can change, so always check the current position before starting work.
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Frequently asked questions
Is the half-width limit based on the plot width?
No. It relates to the width of the original house, not the garden, driveway or ownership boundary. A wide plot does not increase that particular allowance.
Can I add an upper floor above a permitted side extension?
The side enlargement allowance is single storey. A proposed upper floor cannot rely on that allowance and needs its own planning assessment rather than inheriting the ground floor's status.
Does a side return count as rear development only?
Not necessarily. Filling a passage beside an original rear projection may extend beyond an original side wall as well as a rear wall. Both sets of limits can apply.
Will keeping the extension behind the front wall make it permitted?
That may address one issue, but it is not sufficient. Width, height, highway relationships, designated land restrictions, coverage and the complete enlargement must all be checked.