A side extension under permitted development is a single storey extension beyond a side wall of the original house whose width may be no more than half the width of the original house and whose height may not exceed the limit the order sets, and it is the class that a wide side return turns into value. Side extensions are also the right that designated land removes entirely: on a conservation area, a national park, an area of outstanding natural beauty, the Broads or a World Heritage Site the side extension is not permitted at all, and side extension planning permission is then the only route. The side extension rules a developer reads at a viewing are the width, the height, whether the extension would be forward of a principal elevation or nearer a highway than the original, and whether the land is designated, and the side extension permitted development envelope sheet on this site reads the width and the floor area from the original house and zeroes them on designated land. This page sets out the class as the developer reads it.
Half the width, and the width that counts
The width limit is measured against the original house, the house as first built or as it stood on the appointed day, so a house already extended to the side has spent some or all of its right, and the particulars will describe the extended house. The extension is single storey, its eaves and ridge are limited, and where it comes within a distance of a boundary the eaves limit tightens; a side extension may not go forward of the principal elevation or a side elevation fronting a highway. The sheet takes the width of the original rear wall and returns the side width and the floor area along the side wall depth you enter.
Designated land, and why the side return is the common overpayment
Permitted development side extensions do not exist on article 2(3) land, and a developer who prices a wide side return in a conservation area at the standard envelope has bought a planning application, a design review and possibly a refusal. The authority's constraints map shows the designation and any article 4 direction that has withdrawn the class elsewhere, and the sheet takes designated land as an input and zeroes the side width when it is set. The guide on permitted development in a conservation area sets out the rest of what designation removes.
When it becomes an application, and what the file keeps
Side extension planning permission is needed for a two-storey side extension, a width beyond half the original, a side extension on designated land or under an article 4 direction, a flat or a converted house, and a scheme whose combined extensions exceed the curtilage limit. Curtilo Pro keeps the side reading against the plot with the original width, the depth used and the designation read on the day, so the offer and the file agree; the order and the technical guidance cited below are where the figures and the diagrams come from.
Questions people ask about side extension
How wide can a side extension be under permitted development?
No more than half the width of the original house, single storey, within the height limit, and not on designated land. The sheet on this site reads the width from your original house; the order cited below states the rule.
Can a side extension be two storeys?
Not under the class: a two-storey side extension needs a planning application. The class allows single storey only, and the rear class allows two storeys within its own depth limit.
Does a side extension count against the outbuilding limit?
Yes: the total ground covered by everything other than the original house, extensions included, may not exceed the share of the curtilage the order sets, and the sheet reads the outbuilding room after the extensions.
Sources
- legislation.gov.uk, The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2 Part 1: the householder classes, the extension depths and widths, the outbuilding and porch limits and what designated land removes
- GOV.UK, Permitted development rights for householders: technical guidance, the government's reading of Part 1 with diagrams of the original house, the rear and side limits and designated land
- GOV.UK planning practice guidance, Conserving and enhancing the historic environment: conservation areas, listed buildings and what designation changes