Class E outbuildings and the 50 per cent curtilage rule

The outbuilding permitted development 50 per cent rule is the limit most people meet first and understand least. Class E of Part 1 permits buildings within the curtilage of a house for a purpose incidental to its enjoyment, but not if the total area of ground covered by buildings within the curtilage, other than the original house, would then exceed half the area of the curtilage. Sheds, garages, a previous extension built under Class A, a greenhouse and the new garden room all count towards that half.

Two tests sit either side of it. The purpose test decides whether Class E applies at all. The height limits decide what you can build once it does. Fail any one and the building needs planning permission.

The purpose test: incidental to the enjoyment of the house

Class E covers buildings required for a purpose incidental to the enjoyment of the dwellinghouse. Incidental means subordinate to living in the house rather than part of living in it.

A garden office, a gym, a workshop, a store, a home cinema, a garage and a greenhouse are all straightforwardly incidental. A structure containing a bedroom is not, because sleeping is part of the primary residential use rather than incidental to it.

The test is applied to the building's purpose, judged objectively. It is not satisfied by describing a building as a store on the drawings and then moving a relative into it. Councils look at what the building contains and how it is used, and the fittings are evidence rather than the test itself.

One more point that catches people. A use that would be incidental for a household is not incidental if it is a business generating visitors, deliveries or employees. A garden office used by the occupier for their own work is fine. The same building used as a base for a business with staff attending is a different proposition.

Calculating the 50 per cent

The calculation compares two areas. The numerator is the total ground area covered by buildings within the curtilage other than the original dwellinghouse. The denominator is the total area of the curtilage, excluding the ground area of the original dwellinghouse.

Two words do the work.

Original dwellinghouse means the house as it was first built, or as it stood on 1 July 1948 if it is older. Extensions added since then count towards the buildings total, even where they were lawful when built. On a 1930s semi that has been extended twice, the available headroom under the 50 per cent limit can be much smaller than the garden suggests.

Curtilage is the land attached to and serving the house. It is usually the garden, and it does not automatically include a paddock or an adjoining field bought later, even where the same person owns it and the fence has been moved.

Do the sum on a scaled plan and keep it. A simple table listing each structure, its footprint and the running total is the document that answers an enforcement query five years later.

Height limits by roof type and by boundary distance

Class E sets height in three ways, and the distance to the boundary changes which applies.

Height is measured from the highest ground level immediately adjacent to the building, so a sloping garden changes the answer depending on where you stand. Levelling the ground or building on a raised platform changes the measurement too, and raised platforms above 0.3 metres are excluded from the Class in any case.

The 2 metre distance runs from the boundary of the curtilage, which is not necessarily the fence line. Check the title plan where the two might differ.

Position relative to the principal elevation

No part of a Class E building may be situated on land forward of a wall forming the principal elevation of the original house where that wall fronts a highway. In practice that rules out most front garden structures.

On article 2(3) land, which includes conservation areas, National Landscapes, National Parks and World Heritage Sites, two further restrictions apply. Nothing may be built to the side of the house. And a building more than 20 metres from any wall of the house is limited to 20 square metres of ground area. The wider position on permitted development in protected areas is worth checking before designing anything on designated land.

Flats and maisonettes have no Part 1 rights at all, for the reasons set out in this note on why flats and maisonettes have no Part 1 permitted development.

Pools, containers and the structures people ask about

Class E expressly covers swimming and other pools required for a purpose incidental to the enjoyment of the house, subject to the same limits. A pool counts towards the 50 per cent as a structure, and pool plant housing counts as a building.

Oil and liquefied petroleum gas containers for domestic heating are permitted under Class E subject to capacity and height limits set out in the Class, so check the figures in the Order before siting a tank.

Shipping container studios and modular garden rooms raise a different question. Placing a container in a garden can amount to development either as a building operation or as a material change of use, depending on how it is fixed, how permanent it is and what it is used for. Where the unit is delivered complete and sits on a prepared base, it is usually treated as a building and assessed under Class E on its dimensions. Where it is plainly temporary and movable, the position is less clear, which is a good reason to apply for a certificate rather than guess.

Evidence to keep when the building is finished

Permitted development leaves no decision notice, so the only record is the one you create. Keep six things in a single folder:

1. A scaled site plan showing the curtilage boundary, the original house footprint and every building, with areas marked.
2. The 50 per cent calculation, dated.
3. Dimensioned elevations and a section showing the height measurement and the datum used.
4. Photographs during construction, including the base, the frame and the finished building with a measuring staff visible.
5. The invoice and specification, which establish the date and what was built.
6. Any correspondence with the council.

Where the building is close to a limit, or where the house has been extended before, apply for a Lawful Development Certificate for proposed development under section 192 of the Town and Country Planning Act 1990 before starting. It produces a formal decision on the facts and the law, and a compliant proposal is granted. If the building is already up, a certificate for existing development under section 191 does the same job retrospectively, though it is harder work because the evidence has to be assembled after the event. Either way, the certificate is what a purchaser's solicitor will ask for.

Where a certificate is refused or the scheme exceeds the limits, a householder planning application with a short Planning Statement is the route, and outbuildings of a reasonable size in a reasonable position are commonly granted.

This is general guidance, not legal advice. Permitted development rights can be removed by an Article 4 direction or by a condition on an earlier permission, and a Lawful Development Certificate is the only formal way to confirm that works are lawful. Check the position with your local planning authority or a qualified professional before relying on it.

If an application turns out to be needed, enter your postcode on PlanScope to see which reports your site needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.