What Is the Maximum Garden Room Size Without Planning Permission?

If you’re planning a new garden room, one of the first questions you may ask is: How big can it be without planning permission? In the UK, this depends on permitted development rules, which allow certain works to be carried out without applying for planning consent.

Below, we outline the key size, height, and location limits you need to follow to build a garden room without planning permission.

Permitted Development Rules for Garden Rooms

Garden rooms are considered outbuildings and usually fall under Permitted Development Rights in England. These rules also apply to structures like sheds, greenhouses and garages, provided they meet certain criteria.

Your garden room must be:

• For incidental use to the main house (e.g. an office, studio, gym – not a bedroom or annexe)
• Within the curtilage of a single dwelling
• Not on land forward of a wall forming the principal elevation (typically the front of your house)

Maximum Garden Room Size and Height Without Planning

There is no fixed size in square metres, but several conditions define the maximum garden room size without planning permission:

• No more than 50% of the total area of land around the original house can be covered by buildings (including existing sheds, garages, extensions, etc.)
• Single-storey only
• Maximum eaves height: 2.5 metres
• Maximum overall height:
  • 4 metres for a dual-pitched roof
  • 3 metres for any other type of roof (e.g. flat roof)
• If within 2 metres of a boundary, the entire structure must not exceed 2.5 metres in height
• No verandas, balconies or raised platforms (over 0.3 metres high)

Restrictions in Designated Areas

If your home is in a conservation area, National Park, Area of Outstanding Natural Beauty (AONB) or a World Heritage Site, additional limits apply:

• If the garden room is more than 20 metres from the house, it must not exceed 10 square metres in size
• Outbuildings to the side of the property usually require planning permission
• If your home is a listed building, you will need planning permission for any outbuilding

Important: The term “original house” means the property as it was first built, or as it stood on 1 July 1948. Previous extensions still count towards the 50% land coverage rule.

Intended Use: Incidental Only

Your garden room must be used for purposes that are incidental to the enjoyment of the home. This includes:

• Studios
• Home offices
• Home gyms

If your design includes a kitchen, shower room, or sleeping space, it may be classed as a garden room annexe and will likely require planning permission.

👉 Read: Do I need planning permission for a garden room annexe?

Need Help Designing Your Garden Room?

Design for Me connects homeowners with the right architect or garden room designer for their project – it’s quick, easy and free to use.

👉 Read: Six inspiring tips for a multifunctional garden room
👉 Explore: Garden room ideas and inspiration
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This article provides general guidance on permitted development rights for garden rooms in England. Planning regulations may vary based on individual properties, previous extensions, and local authority policies.

We strongly recommend speaking to your local planning authority or a qualified planning professional before starting your project.

You can find more information in the UK Government’s official Technical Guidance on Permitted Development Rights.