Do I need planning permission for a garden room?

The main permitted development conditions

Permitted development for outbuildings in England is set out in the General Permitted Development Order. In broad terms, an outbuilding needs to be incidental to the enjoyment of the house and stay within limits on size, height and position.

• Single storey only, with no balconies, verandas or raised platforms above the set height
• Maximum overall height of four metres for a dual pitched roof, three metres for other roofs
• Within two metres of a boundary, the maximum height drops to two and a half metres overall
• Outbuildings must not sit forward of the principal elevation facing a highway
• Total ground covered by outbuildings must not exceed half the land around the original house

Where permitted development stops applying

These are the cases where an application is usually needed, and where assuming otherwise is expensive.

• Listed buildings, where listed building consent is a separate and stricter requirement
• Conservation areas, national parks and areas of outstanding natural beauty, where limits tighten
• Flats and maisonettes, which do not have these outbuilding rights
• Homes where permitted development rights have been removed by condition or an article 4 direction
• Any building containing sleeping accommodation, which is not incidental use If the building is for someone to live in, the rules for garden annexes apply instead.

Incidental use, and why sleeping changes everything

Permitted development covers buildings incidental to the enjoyment of the house: an office, a gym, a hobby room, storage. A building someone lives or sleeps in regularly is not incidental, it is separate accommodation, and that needs planning permission and brings building regulations with it.

Occasional guests are a grey area that councils view differently. If the intention is a granny annexe or a let, treat it as an annexe project from day one rather than hoping the label holds.

Building regulations are separate

Planning and building regulations are two different systems, and satisfying one says nothing about the other. A detached outbuilding under fifteen square metres with no sleeping accommodation is generally exempt from building regulations, with further conditions between fifteen and thirty square metres relating to distance from boundaries and construction materials.

The electrical installation is always in scope of Part P regardless of the size, and adding a shower, WC or sleeping space brings the building regulations firmly into play.

Proving it later: lawful development certificates

If you want documentary comfort that your garden room was lawful, you can apply to the council for a lawful development certificate. It is not compulsory, but it is useful when selling, because a buyer's solicitor may ask what authorised the building.

Practical order of checks

Before ordering anything, work through this in order and you will avoid nearly every common problem.

• Check the property is a house, not a flat, and is not listed
• Check whether you are in a conservation area or similar designation
• Check the title and any planning conditions for removed permitted development rights
• Measure the proposed height and distance to boundaries against the limits
• Add up existing outbuilding coverage across the garden
• Ring the council's planning duty line and confirm before you commit