Class E outbuildings and the incidental use test
A garden office usually falls within Class E permitted development. A garden bedroom usually does not. The incidental use test, the height limits and the 50 per cent curtilage rule explained.
A garden office is usually fine under Class E outbuilding permitted development. A garden bedroom usually is not. That single distinction decides most of the enquiries councils receive about garden rooms, because Class E of Schedule 2 Part 1 of the GPDO 2015 permits buildings within the curtilage of a house only where they are required for a purpose incidental to the enjoyment of the dwellinghouse as such. Everything else in the class is dimensional, and the dimensions are easier to satisfy than the use test.
What incidental means, and what it quietly excludes
Incidental means a use that supports the enjoyment of the house without forming part of the main living accommodation. A gym, a home office, a workshop, a store, a pool house, a garage, a summerhouse. All ordinary examples.
Primary living accommodation is a different thing. Sleeping accommodation, a main kitchen, a self-contained annexe used as someone's home. Those are generally treated as ancillary to the dwelling rather than incidental to it, and the case law on Class E has long drawn that line. The class does not authorise them, so a garden building with a bed in it is on shaky ground even when every measurement complies.
The test also has an element of reasonableness attached to the particular house. A modest store for a terraced cottage is plainly incidental. A very large building justified as a hobby space, on a small plot, invites the officer to ask whether it is really required for a purpose incidental to the enjoyment of that dwelling. The only formal way to settle that question is a lawful development certificate.
Height, and the two metre boundary rule that catches everyone
The height limits sit in the E.1 conditions and depend on the roof and on where the building sits.
| Situation | Maximum height |
|---|---|
| Dual-pitched roof, more than 2m from the boundary | 4 metres |
| Any other roof, more than 2m from the boundary | 3 metres |
| Any building within 2m of the curtilage boundary | 2.5 metres |
| Eaves, in all cases | 2.5 metres |
The two metre rule is measured to the boundary of the curtilage, not to the neighbour's building, and it applies if any part of the outbuilding falls within that distance. Pushing a flat-roofed garden room hard against the back fence therefore caps it at 2.5 metres, which after floor build-up and a shallow fall leaves a tight internal height. Moving it 2.1 metres off the boundary buys you half a metre.
Two further limits. The building must be single storey, and it must not be forward of a wall forming the principal elevation of the original dwellinghouse. Original means as built, or as it stood on 1 July 1948, which matters on properties that have already been extended.
Balconies, verandahs and raised platforms are excluded from the class entirely. A raised platform means one more than 0.3 metres high, so a decked terrace at 400mm above ground level needs planning permission even though the decking itself feels like landscaping.
The 50 per cent curtilage test
Class E is not permitted where the total area of ground covered by buildings, enclosures and containers within the curtilage, other than the original dwellinghouse, would exceed half the total area of the curtilage excluding the ground area of the original house.
Read that carefully, because it catches cumulative development. Earlier extensions built under Class A count towards the buildings side of the calculation. So do existing sheds, a detached garage, a greenhouse and, on the wording, containers such as an oil tank enclosure. On a large plot the test is academic. On a small terraced garden with an existing side extension and a shed, it can be the binding constraint.
Do the arithmetic on the site plan before you design. Measure the curtilage, subtract the footprint of the original house, halve the remainder, then total everything already built plus the proposal.
Garden offices, and where working from home stops being incidental
A room used as a home office for the occupier's own work is incidental. The use only becomes a planning problem when the character of the use of the property as a whole changes, which is the ordinary material change of use test.
The markers officers look for are familiar. Staff coming to the site. Customers visiting. Deliveries beyond what a household generates. Signage. Vehicles or storage that alter the appearance of the property. A single person answering emails in a garden room triggers none of them. A two person business with clients arriving for appointments plainly might.
Where the business use is real and visible, the honest route is a full application with a short Planning Statement explaining hours, visitor numbers, parking and how the residential character is preserved. Councils grant these regularly, often with conditions limiting hours and staff numbers.
Annexes, dependent relatives and the separate dwelling trap
An annexe for an elderly parent is the most common reason people ask about Class E, and it is the least likely to fit. Living accommodation is not incidental, so the class does not cover it.
There are two lawful routes. The first is planning permission for an annexe as ancillary accommodation, usually conditioned so that it cannot be occupied or sold separately from the main house. The second is permission for a fully separate dwelling, which brings a change of use, a new planning unit, and potentially a Community Infrastructure Levy liability with a self-build exemption that must be claimed before work starts.
What determines which one you have is the facts rather than the label. Whether the building has its own kitchen, its own entrance, its own garden and its own council tax band, and whether it is used as a separate household. Building something as a hobby room and moving a relative in afterwards is a change of use, and enforcement officers see it often.
Conservation areas and other article 2(3) land
On article 2(3) land, which covers conservation areas, National Parks, National Landscapes, World Heritage Sites and the Broads, Class E is cut back. Development is not permitted where the total area of ground covered by buildings situated more than 20 metres from any wall of the house would exceed 10 square metres.
In a long conservation area garden that is severe. A 4 metre by 3 metre studio at the bottom of the plot exceeds it. The workaround, where the design allows, is to bring the building within 20 metres of the house, measured from any wall rather than the rear wall.
Within the curtilage of a listed building, Class E does not apply at all, and listed building consent may be needed for a curtilage structure. Where the house is listed or the setting of a listed building is affected, a Heritage Statement assessing significance is what the conservation officer will expect with any application. An Article 4 direction can remove Class E rights entirely, so check the council's Article 4 register as well.
Get the certificate before you pour the slab
A Lawful Development Certificate for proposed use or development, under section 192 of the Town and Country Planning Act 1990, is the only formal way to confirm that works are lawful. It is decided on the facts and the law rather than on planning merit, and it costs half the fee of the equivalent planning application.
Submit scaled existing and proposed plans, elevations with heights dimensioned from the correct ground level, a site plan showing the curtilage area and the 50 per cent calculation, and a short statement identifying the intended incidental use. Get the certificate before you build and the position is settled. Try to get one afterwards and you are relying on the evidence of what you actually did.
If the certificate route fails, a full householder application is not a defeat. Browse the supporting documents a small application typically needs and the pack is usually short.
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. Enter your postcode on PlanScope to see which documents a garden building application is likely to need.
Frequently asked questions
Can I sleep in a garden room built under Class E?
Class E permits buildings required for a purpose incidental to the enjoyment of the house. Sleeping accommodation is generally treated as part of the main living accommodation rather than incidental, so it falls outside the class. Using a compliant outbuilding as a bedroom risks enforcement action. A lawful development certificate is the only way to settle the point.
How tall can a garden room be near the boundary?
If any part of the building sits within two metres of the curtilage boundary, the height limit is 2.5 metres. Beyond two metres, a dual-pitched roof may reach four metres and any other roof three metres, with eaves capped at 2.5 metres throughout. Moving the building just over two metres off the fence buys useful height.
What is the 50 per cent curtilage rule?
Class E does not permit development where buildings, enclosures and containers within the curtilage, excluding the original house, would cover more than half the curtilage area once the original house footprint is deducted. Earlier extensions, sheds and garages all count, so the calculation has to include what is already built.
Do conservation areas change Class E outbuilding rights?
Yes. On article 2(3) land, which includes conservation areas, National Parks, National Landscapes, World Heritage Sites and the Broads, buildings more than 20 metres from any wall of the house are limited to 10 square metres in total. Class E does not apply at all within the curtilage of a listed building.
Is a raised deck covered by Class E?
No. Class E excludes verandahs, balconies and raised platforms, and a raised platform means one more than 0.3 metres above ground. A deck at 400mm therefore needs planning permission even though it looks like landscaping. Keeping the finished surface below 300mm avoids the issue on most level gardens.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.