Outbuildings with a shower room or kitchenette

A garden outbuilding can have a WC and a basin and stay within permitted development. Add a shower, a kitchen and a bed and it will fall outside those rights, because Class E of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 only permits buildings incidental to the enjoyment of the dwellinghouse, and a building fitted out for independent living is not incidental to anything.

The fittings themselves are not the test. What matters is what the combination of them says about how the building will be used.

What Class E actually permits

Class E covers buildings and enclosures within the curtilage of a house, provided they are required for a purpose incidental to the enjoyment of that house. The dimensional limits are the part most people know.

• Single storey, with eaves no higher than 2.5 metres.
• Maximum overall height of 4 metres with a dual pitched roof, or 3 metres otherwise.
• Maximum height of 2.5 metres in total where any part is within 2 metres of a boundary.
• Nothing forward of a principal elevation fronting a highway.
• Buildings, including the outbuilding, covering no more than half the curtilage excluding the original house.
• No verandas, balconies or raised platforms.

On article 2(3) land, which includes conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites, outbuildings at the side of the house are excluded and anything over 10 m² more than 20 metres from the house falls outside the class. Within the curtilage of a listed building, Class E does not apply at all.

Meet every dimension and you can still fall outside Class E on the purpose test alone. That is the trap.

Incidental is narrower than ancillary

These two words are used interchangeably in conversation and they mean different things in planning.

Ancillary describes something that supports the main use of the land. A bedroom for a relative in a garden building is ancillary to the use of the site as a single dwelling, so it does not create a second dwelling.

Incidental is narrower. It describes something subordinate to the main use rather than part of it, and the courts have held that primary living accommodation is not incidental to a dwellinghouse, because living is the house's main purpose. A home office, a gym, a workshop, a store, a pool building or a garden room for reading in are all incidental. A bedroom is not.

So a garden building used as a spare bedroom for family is ancillary but not incidental. It does not create a separate planning unit, and it still needs planning permission, because Class E does not cover it. That distinction catches out a lot of people who have correctly worked out that they are not making a new dwelling.

The separate question of when accommodation becomes a dwelling in its own right is dealt with in annexe or separate dwelling: where the line falls.

Facilities that usually pass and facilities that do not

There is no list in the Order, so this is drawn from how the purpose test is applied in practice rather than from statute.

Read the table as a set rather than line by line. A shower on its own beside a gym is unremarkable. The same shower alongside a full kitchen and a bed space describes a self-contained unit, and an officer or an enforcement investigator will read it that way whatever the planning application called the rooms.

Where you want the building to have all of those things, apply for planning permission. It is a householder application, the fee is modest, and a permission removes the risk permanently. What a permission will usually carry is a condition tying the building to use ancillary to the main house and preventing separate occupation, and offering that condition yourself is the fastest route to a decision.

Sleeping accommodation and where the line falls

Occasional use of a garden room by a guest for a night or two is not, on its own, what turns a building into accommodation. Permanence and facilities are what do it.

Three factors do most of the work. Whether the building can be lived in without using the main house at all, which is decided by the presence of cooking and washing facilities together. Whether there is a permanent sleeping arrangement rather than a sofa bed. And whether the occupant is part of the household or someone with their own separate domestic life on the plot.

A home office with a shower, a sink and a sofa bed used twice a year by visiting relatives sits on the incidental side of the line in most officers' judgement. A building with a kitchen, a bathroom, a bedroom and its own entrance does not, however it is described.

The safest course where sleeping use is intended at all is to apply. A refusal is uncommon on a modest garden building, and the condition that follows is one you can live with.

Drainage, Building Regulations and the 30 m² exemption

Planning is only half of it, and this is where the practical costs sit.

Detached single storey buildings under 30 m² are exempt from most Building Regulations requirements, subject to conditions about their position relative to boundaries and their construction, and critically on the basis that they contain no sleeping accommodation. Adding a bedroom removes the exemption and brings the whole building into control, including insulation, ventilation and fire safety requirements.

Adding a WC or shower brings controlled services into play regardless of the exemption. New sanitary appliances and the drainage serving them are notifiable work, the connection to the foul drain has to be made properly, and electrical work in the building is notifiable under the electrical safety requirements.

Two site issues arrive with the drainage. Where the new run crosses or approaches a public sewer, the sewerage undertaker's agreement may be needed, and since the transfer of private sewers many garden drainage runs are now public. And where the connection is to a septic tank or treatment plant, the additional load needs checking against its capacity.

Get a drainage route agreed before the slab is poured. Retro-fitting a soil connection across a finished garden costs several times what it costs to plan for.

Guests, lodgers and letting it out

Letting a garden building out, whether on a long tenancy or as a short-term let, is a different use of the land from using it as part of your home.

At the point where someone occupies it as their own separate household, paying rent and living independently, the building becomes a separate dwelling. That is a material change of use requiring planning permission, it will usually be resisted where the plot cannot support a second dwelling on access, amenity space and privacy grounds, and it can be enforced against.

Short-term letting is less clear cut and depends on frequency, exclusivity and whether the main house continues to function as one household. Regular letting of a self-contained garden building, advertised separately with its own access and key, is a long way from occasional guest use.

Council tax and, in some areas, licensing sit alongside this. A separately banded garden building is evidence of self-containment, and while banding does not decide the planning position, it is the kind of evidence an enforcement officer will find quickly.

Describing the use honestly

Whatever route you take, describe the building by what it will be.

Label the rooms on the drawings by actual use. A room with a bed in it is a bedroom, not a store. A room with a cooker is a kitchen, not a utility. Misdescription achieves nothing useful: a permission granted for a home office does not authorise a bedroom, and a lawful development certificate obtained on the basis of a false description can be revoked.

Where an application is needed, a short Planning Statement setting out the intended use, the relationship to the main house, the shared garden and access, and the ancillary use condition you are offering, will carry most modest schemes. For a property in a conservation area or within the curtilage of a listed building, a Design and Access Statement is likely to be required too, and Class E is either restricted or unavailable in those settings.

This is general guidance, not legal advice; whether a particular outbuilding is incidental depends on its facilities and its intended use, so check with your local planning authority or a qualified professional before building. A Lawful Development Certificate is the only formal way to confirm that works and uses are lawful.

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