Outbuildings under Class E and the 2.5 metre rule

If any part of a garden building sits within 2 metres of the boundary of your curtilage, its overall height cannot exceed 2.5 metres and it stays permitted development. Move it further in and you get 4 metres for a dual-pitched roof or 3 metres for anything else. That single limit, the Class E outbuilding 2.5 metres rule in Part 1 of Schedule 2 to the General Permitted Development Order 2015, decides the shape of most garden rooms, home offices and sheds in England, and it is measured in a way that catches people out.

What Class E actually permits

Class E allows the provision, within the curtilage of a dwellinghouse, of a building or enclosure, a swimming pool or other pool, required for a purpose incidental to the enjoyment of the dwellinghouse. It also covers a container used for domestic heating oil or liquid petroleum gas. The right belongs to dwellinghouses only. Flats and maisonettes have no Part 1 rights at all, so a shed in the garden of a converted flat needs permission.

The word doing the work is incidental. A home office, a gym, a games room, a workshop for a hobby, a garden store and a pool house are all incidental to living in the house. Sleeping accommodation is not. Nor is anything that amounts to a separate dwelling, with its own kitchen, bathroom, entrance and independent occupation. If the building is intended as a self-contained annexe, Class E is the wrong route and you need either a householder application or a full application depending on how the council reads the planning unit.

Primary living accommodation sits in an awkward middle. A council will usually accept a garden room used occasionally as a snug or a studio. It will not accept a building that becomes the household's main kitchen and living room, because that is an extension of the dwelling rather than something incidental to it.

Measuring the 2.5 metre limit near a boundary

Height under Class E is measured from the highest part of the surface of the ground next to the building, not from the floor level inside and not from an average. On a sloping garden that means the uphill side governs, which is why a building that looks 2.4 metres tall on the drawings can measure 2.7 metres on site once the ground is surveyed properly.

The 2 metre test is about the boundary of the curtilage, not the fence line of your registered title and not the neighbour's wall. Where the curtilage boundary runs along the inside face of a shared fence, measure to that. The 2.5 metre cap applies if any part of the building is within 2 metres, so a building set at an angle with one corner clipping the zone takes the lower limit across the whole structure.

The practical consequence is a flat or very shallow mono-pitch roof, a build-up of around 150 to 200 millimetres for floor, insulation and finish, and an internal head height of a little over 2.2 metres. That is workable for an office. It is tight for a gym with overhead lifts, and it is the reason so many garden rooms end up 2 metres and a bit off the boundary rather than hard against it.

Eaves height is capped at 2.5 metres wherever the building stands, and the building must be single storey. A balcony, a veranda or a raised platform takes it outside Class E, and a raised platform means anything with a surface more than 0.3 metres above the ground. Decking at 400 millimetres on a sloping plot has caught out a lot of people who thought the rules only applied to the shed. The same logic applies to terraces on houses, which we look at in the piece on Juliet balconies, terraces and overlooking.

The 50 per cent curtilage test

Class E is not permitted if the total area of ground covered by buildings, enclosures, pools and containers within the curtilage, other than the original dwellinghouse, would exceed 50 per cent of the area of the curtilage excluding the ground area of the original dwellinghouse.

Three things make this harder than it reads. The baseline is the original dwellinghouse, meaning the house as built or as it stood on 1 July 1948, so a rear extension added in 1995 counts towards the 50 per cent rather than being excluded with the house. Everything counts, including an existing detached garage, a greenhouse and a bin store. And the curtilage is the land used with the house, which is not automatically the whole of a large plot with a paddock beyond it.

Work the arithmetic before you choose the building, not after. On a small terraced plot with an existing side extension and a garage, the available footprint can be less than a stock 4 by 3 metre garden room.

Forward of the principal elevation and designated land

Nothing under Class E may sit on land forward of a wall forming the principal elevation of the original dwellinghouse. For most houses that means nothing in the front garden, including a bin store, a bike shed or an oil tank. The principal elevation is normally the one facing the highway and containing the main architectural interest, though on a corner plot it is worth settling with the council rather than assuming.

On article 2(3) land, which covers conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites, buildings more than 20 metres from any wall of the house are limited to 10 m² of ground coverage in total. Within the curtilage of a listed building, Class E does not apply at all, so a garden office next to a listed house needs planning permission and may need listed building consent if it affects the setting or involves works to curtilage structures. A Heritage Statement is then part of the pack, and the council's assessment runs through sections 16 and 66 of the Planning (Listed Buildings and Conservation Areas) Act 1990.

Article 4 directions can remove Class E entirely over a defined area. They are common in conservation areas and in some estate-wide designations, and the schedule to each direction names precisely which classes are withdrawn.

Services, heating and what sits alongside Class E

A garden room with power, water and drainage is still incidental, and running a supply to it does not change the analysis. Foul drainage connected to the public sewer may need the undertaker's consent under the Water Industry Act 1991. An air source heat pump serving the house or the outbuilding has its own permitted development route with its own conditions, set out in Class G of Part 14, and those conditions are covered in our note on air source heat pumps and the conditions attached.

Trees are the other common constraint. Where a protected tree stands nearby, the root protection area calculated under BS 5837:2012 may rule out traditional strip foundations, and a screw pile or ground beam solution becomes the only way to build without works that would need consent under the Tree Preservation Regulations 2012.

Proving the building is lawful

Permitted development gives you no paperwork. If you want certainty, apply for a lawful development certificate under section 192 of the Town and Country Planning Act 1990 before you build, or under section 191 for something already standing. The council tests the proposal against the Class E limits and issues a certificate if it complies. It is the only formal way to confirm that works are lawful, and it is what a buyer's solicitor will ask for in five years' time.

Keep the evidence either way: a measured survey showing ground levels, the setting-out dimensions to the curtilage boundary, a footprint calculation for the 50 per cent test, and dated photographs. The immunity period for unauthorised building works in England was extended by the Levelling-up and Regeneration Act 2023, so check the current position rather than relying on an older four-year assumption.

Where a Planning Statement is needed because the building falls outside Class E, it should deal with scale, overlooking, the relationship to the boundary and the incidental purpose, and nothing else.

Enter your postcode on PlanScope to see whether a garden building on your plot needs an application and which documents would go with it.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.