Garden rooms and the incidental enjoyment test
Class E permits garden buildings for purposes incidental to the enjoyment of a house. Which uses fall outside that, what the height and coverage limits are, and what a certificate proves.
A garden room is permitted development only while its use stays incidental to the enjoyment of the house. Garden room incidental use is a test about purpose, not about dimensions, so a building that meets every height and coverage limit in Class E can still be unlawful because of what happens inside it. Home offices, gyms and playrooms are generally fine. Bedrooms, self contained annexes and a business with customers coming to the door are not.
Work out which side of the line your use falls on before you buy the building, because the supplier's brochure will not tell you.
What incidental to the enjoyment means
Class E of Schedule 2 Part 1 to the General Permitted Development Order 2015 permits a building or enclosure "required for a purpose incidental to the enjoyment of the dwellinghouse". Incidental means subordinate to the main residential use, and serving it.
The courts have treated this as an objective test rather than a matter for the occupier to decide. What the householder wants is relevant, but the question is whether the use is reasonably to be regarded as incidental to the enjoyment of a dwellinghouse of that character, judged objectively. A householder cannot make a use incidental simply by declaring it to be so.
In practice, uses that read as an extension of ordinary domestic life pass: a study or home office used by the household, a gym, a garden store, a hobby room, a playroom, a summer house, a pool or a garage. Uses that supply a function of the dwelling itself are the difficulty, because they tend to be part of the primary accommodation rather than incidental to it.
Uses that fall outside it
Four recurring problems.
Primary living accommodation. A kitchen, a living room or a bedroom in an outbuilding is not incidental to the enjoyment of the house. It is part of the accommodation, and moving a dwelling's essential rooms into a separate building changes the character of what is on the plot.
Self contained accommodation. A garden building with a kitchen, a shower and a bedroom is a separate unit whether or not anyone calls it an annexe. That is a material change of use, and it usually needs planning permission for a new dwelling, with all the policy tests that brings, including the ones on separate units in back gardens.
Letting. A garden room let to a lodger or on a short term basis is a commercial use, not an incidental one.
Business use beyond the domestic. A home office used by the resident is different from a treatment room with clients arriving, a workshop with employees, or storage for stock and deliveries.
Where the intention is genuine additional living space in a separate building, the position is set out in our note on converting an outbuilding into habitable accommodation.
Sleeping accommodation in an outbuilding
This is the question asked most often, and the answer sits between the two extremes people expect.
Occasional use of an incidental building for sleeping, by a household member or a guest, does not by itself convert an ancillary garden room into a separate dwelling. What matters is the overall character of the use. A room fitted out as a bedroom, with a bathroom attached, occupied regularly by a member of the household who otherwise lives independently of the main house, is a different proposition from a summer house where a teenager sometimes sleeps in August.
Officers look at the fit out and the facilities as evidence of intended use. A shower room, a kitchenette, a separate meter, a separate entrance from the street and a postal address all point one way. A single room with a socket and a radiator points the other.
If regular sleeping accommodation is the intention, treat it as an application rather than a risk. Enforcement in this area is driven by neighbour complaints, and a building that has been used as a bedroom for two years is harder to regularise than one that was applied for.
Height limits by roof form and position
The dimensional limits are where most attention goes, and they are straightforward.
| Situation | Maximum height |
|---|---|
| Dual pitched roof, more than 2 metres from any boundary | 4 metres |
| Any other roof form, more than 2 metres from any boundary | 3 metres |
| Within 2 metres of a boundary of the curtilage | 2.5 metres |
| Eaves height, in all cases | 2.5 metres |
Height is measured from the highest part of the adjacent ground surface, which matters on a sloping garden. Single storey only, no balcony or veranda, and no raised platform above 0.3 metres.
On article 2(3) land, which includes conservation areas, National Parks and World Heritage Sites, a building is not permitted development if it sits more than 20 metres from any wall of the house. Within the curtilage of a listed building, Class E does not apply at all, so a garden room at a listed house needs planning permission and may need listed building consent depending on its effect on the setting and on any curtilage structures.
Curtilage coverage and the 50 per cent rule
The coverage limit catches plots where outbuildings have accumulated over the years.
Class E does not permit development where the total area of ground covered by buildings within the curtilage, other than the original dwellinghouse, would exceed 50 per cent of the total area of the curtilage excluding the ground area of the original house.
Two points of detail. "Original dwellinghouse" means the house as built, or as it stood on 1 July 1948, not the house as extended, so a large rear extension counts towards the covered area. And the calculation includes every outbuilding, including the shed at the bottom of the garden and any previous extensions beyond the original footprint.
On a modest plot with an extension already built, the 50 per cent figure can be reached faster than owners expect. Measure it rather than assuming, and where a garden building is going near a public sewer, the separate constraint discussed in our note on extending over a public sewer in a back garden applies to outbuildings too.
Business use and when it needs permission
Working from home rarely needs permission. The test is whether the overall character of the use of the property remains residential, or whether a material change of use has occurred under section 55 of the Town and Country Planning Act 1990.
Indicators that a material change has occurred:
- customers, clients or patients visiting the property
- employees working there who do not live there
- deliveries or collections beyond a domestic pattern
- signage, or advertising the address as business premises
- noise, smells or hours of operation unlike a dwelling
- parking demand generated by the business
One or two of those do not settle it. A pattern of them does, and it is a question of degree that a council judges on the facts. Someone writing software in a garden room is not changing the use of a house. Someone running a dog grooming business with six appointments a day is.
Certificates and what they prove
Nothing is issued when a building is permitted development, which is why people end up seeking confirmation later.
A lawful development certificate is the only formal way to confirm that works or a use are lawful. Section 192 of the Town and Country Planning Act 1990 covers a proposed use or operation, and section 191 covers what already exists. For a garden room, a section 192 certificate obtained before building is the cleanest outcome, because it fixes the position on the use as well as the structure.
What a certificate does not do is authorise a later change. A certificate confirming a home office does not cover a subsequent conversion to a bedroom, and the use can drift into unlawfulness without anyone doing any building work at all. That is the part people find counter intuitive, and it is worth explaining in the application itself, which is where a short Planning Statement does the work.
Keep the paperwork: the certificate, the drawings, the supplier specification, and dated photographs. Building regulations are separate again, and most small outbuildings under 15 square metres with no sleeping accommodation are exempt, with a further exemption up to 30 square metres subject to distance from the boundary and construction materials.
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Frequently asked questions
Can I sleep in my garden room?
Occasional use for sleeping by a household member or guest does not by itself create a separate dwelling. Regular use as a bedroom, particularly with a shower room and kitchenette attached and a separate entrance, points towards self contained accommodation, which needs planning permission. The fit out is treated as evidence of the intended use.
How high can a garden room be?
Four metres with a dual pitched roof, three metres with any other roof form, and 2.5 metres where any part of the building is within two metres of a boundary of the curtilage. Eaves are limited to 2.5 metres in all cases. Height is measured from the highest part of the adjacent ground, which matters on a slope.
What is the 50 per cent curtilage rule?
Class E does not permit a building where the ground area covered by buildings other than the original dwellinghouse would exceed half the curtilage excluding the footprint of that original house. Original means as built or as it stood on 1 July 1948, so extensions count towards the total along with every existing outbuilding.
Do I need permission to run a business from a garden office?
Only if the overall character of the property's use stops being residential, which is a material change of use under section 55 of the Town and Country Planning Act 1990. Clients visiting, staff who do not live there, deliveries beyond a domestic pattern, signage and business parking demand are the indicators councils weigh together.
Does Class E apply at a listed building?
No. Class E does not permit buildings within the curtilage of a listed building, so a garden room at a listed house needs planning permission. Listed building consent may also be required depending on the effect on the setting of the building and on any curtilage structures such as walls or outhouses.
How do I prove the garden room is lawful?
Apply for a lawful development certificate. Section 192 of the Town and Country Planning Act 1990 covers a proposed operation or use and is the cleanest route before building, because it fixes the position on the use as well as the structure. Section 191 covers what already exists.
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.