Permitted development for extensions is class A of the householder classes, the right to enlarge a dwellinghouse without an application within limits that read together: the rear depth by house type, the side width as half the original, the two-storey rear within its own depth and distance from the rear boundary, the eaves and ridge heights, the boundary rule at the eaves, no extension forward of a principal elevation, no more than half the curtilage covered with everything else built, materials of similar appearance, no balconies, verandas or raised platforms, and none of it on designated land beyond the plainest rear extension. Permitted development extension rules read as one envelope rather than a list, and the semi detached extension rules are the same class with the attached-house depth and the shared boundary at the eaves. Permitted development as a whole is the General Permitted Development Order, and extension permitted development is the class a developer reads first on any house, because it is where the value in a plot usually sits; the side extension permitted development envelope sheet on this site reads the rear, the side and the outbuilding room together. This page sets out the class in one reading.
The original house, and the envelope that has already been spent
Every limit reads against the original house, so the first reading on any house is whether it has been extended: an extended rear wall has used part of the rear depth, a side extension has used the side width, a conservatory counts, and the particulars will describe the house as it stands. The developer measures the original from the deeds, the old plans or the brickwork and reads the class from that, and the sheet on this site asks for the original width and depth for exactly this reason.
The limits every extension shares
Whatever the extension, the ridge may not exceed the highest part of the existing roof, the eaves may not exceed the existing eaves, an extension within a distance of a boundary has a lower eaves limit, nothing goes forward of a principal elevation or a side elevation fronting a highway, the materials must be of similar appearance, and the total ground covered by extensions and outbuildings together may not exceed the share of the curtilage the order sets. The two-storey rear has its own shorter depth and a minimum distance from the rear boundary, and side-facing upper windows must be obscure-glazed and non-opening below a height.
Where the class stops, and what the file keeps
The class does not apply to a flat, to a house made by a change of use under the order, to a house under an article 4 direction that withdrew it, or on designated land beyond the single storey rear at the standard depth; and it does not include a balcony, a veranda, a raised platform or a chimney beyond its own limit. Curtilo Pro keeps the class A reading against the plot with the original measurements, the designation and the extensions already standing, so the envelope the offer was built on is the one the file shows; the order and the technical guidance cited below are where the figures and the diagrams come from.
Questions people ask about permitted development for extensions
What is the difference between permitted development and planning permission?
Permitted development is permission granted by the order itself, for classes of development within limits, without an application; planning permission is granted by the authority on an application. A scheme outside the class needs the application, which is consentvia.com's side.
Do the semi detached extension rules differ from a detached house?
In the rear depth, which is shorter for an attached house, and in the boundary at the eaves along the shared side. The side width, the heights and the curtilage limit are the same. The sheet reads the depth from the house type.
Can I combine a rear extension and a side extension under the class?
Yes, within the limits of each and the curtilage limit for both together, and a wrap-around that joins them is read as one enlargement against both limits. The sheet reads the areas separately and the room left for outbuildings after them.
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, When is permission required: development, permitted development rights, prior approval and article 4 directions