KNOW THE RULES

Do I need planning permission for a garden room or outbuilding?

Usually no planning permission needed if size and height limits are met, but building regulations and exceptions can still apply.

AB-01The short answerIt depends. Most garden rooms and outbuildings fall under 'permitted development' and don't need planning permission, as long as they meet size, height and position limits. If you go over those limits, or live somewhere with extra restrictions, you will need to apply.
AB-02This guide covers England firstThe rules below are for England. Permitted development rights and Building Regulations exemptions are set separately for Wales, Scotland and Northern Ireland. Check the step at the end if you live outside England.
AB-03The size and position limits that decide itIn England, permitted development usually covers single-storey outbuildings with an eaves height up to 2.5m, and an overall height up to 4m with a dual-pitched roof or 3m otherwise. Within 2m of a boundary, the height limit drops to 2.5m. It must not sit forward of the front of the house, and outbuildings plus any previous extensions must not cover more than half the garden.
RULES
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These limits come from the General Permitted Development Order; going over them means you legally need planning permission.

AB-04Exceptions that change the answerFlats and maisonettes don't get these permitted development rights at all — any outbuilding usually needs planning permission. If your house is listed, outbuildings in its grounds are not permitted development, so you need planning permission, and listed building consent may be needed too. Conservation areas, other designated land, and Article 4 directions can remove or shrink your permitted development rights. If the house has been extended before, that work counts towards your 50% garden coverage limit. Leasehold terms or covenants can also restrict what you're allowed to build, even if planning permission isn't needed.
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Listed building consent is a separate legal requirement, and breaching it is a criminal offence.

AB-05Planning permission and Building Regulations are separateNot needing planning permission does not mean you're exempt from Building Regulations, and vice versa. A detached single-storey outbuilding under 15m² usually doesn't need Building Regulations approval if it has no sleeping accommodation. Between 15m² and 30m², it's often exempt too, but only if it's at least 1m from any boundary or built from largely non-combustible materials. Check both separately before you build.
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Building Regulations compliance is a legal duty, separate from planning permission.

AB-06Who to ask and howUse the Planning Portal's interactive guidance to check permitted development for your specific plot. If you want certainty in writing, apply to your council for a Lawful Development Certificate. For Building Regulations, contact your council's Building Control team or a registered building control approver. If electrics or gas are involved, use a competent person scheme or Gas Safe Register installer. If the outbuilding sits on or near a shared boundary wall, a party wall surveyor may be needed.
AB-07Costs and timescalesIn England, a Lawful Development Certificate costs £274 and a householder planning application £548, at the rates in force from April 2026. Councils normally decide within 8 weeks. Fees rise most years, so check the current figure on the Planning Portal before applying.
AB-08What happens if you skip itThe council can issue an enforcement notice and make you alter or remove the building, sometimes years after it's built. Unauthorised work can hold up or kill a house sale when the buyer's solicitor asks for proof of compliance. An indemnity insurance policy can sometimes paper over the gap, but it doesn't make the work legal and won't help if the council takes action before you sell.
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Councils have a legal power to enforce against breaches of planning control and Building Regulations.

AB-09If you live in Wales, Scotland or Northern IrelandWales has its own permitted development rules and fees, checked via the Planning Portal Wales. Scotland uses a different permitted development framework and a single-storey garden building of up to 30 m², at least 1 m from the boundary and with no flue, stove or toilet, usually doesn't need a building warrant, but bigger ones do; check mygov.scot before you start. Northern Ireland runs its own planning system entirely separate from GB; check nidirect for the current rules and limits.

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