Garden rooms and Green Belt in Herts & Bucks

The short answer

Green Belt is a planning policy, not a ban. Two different tests can apply to a garden room there.

• Permitted development. If the room meets the outbuilding limits, you may not need an application at all.
• Planning policy. If you do need permission, Green Belt policy sets a higher bar than in other places.

Permitted development in the Green Belt

The government's technical guidance for outbuildings (Class E) and the Planning Portal both list the land where the rules are tighter. They name conservation areas, National Parks, AONBs, World Heritage Sites, the Broads and listed buildings. Neither source mentions Green Belt in the list. So, as far as these sources go, the usual limits apply:

• It must be single storey, with eaves no higher than 2.5 m.
• It can be up to 4 m high with a dual-pitched roof, or 3 m high with any other roof.
• If any part is within 2 m of a boundary, the whole building can be no higher than 2.5 m.
• Height is measured from the highest ground right next to the building.
• It must not sit forward of the front wall of the house (the principal elevation).
• All extensions and outbuildings together must cover no more than half the land around the original house.
• No verandas, balconies or raised platforms. A platform must be no higher than 0.3 m.
• The use must be "incidental" to the house. A bedroom, bathroom or kitchen does not count.

Confirm this with your council. They can also tell you whether an Article 4 direction or an old planning condition removed the rights on your plot. Our planning permission guide covers the checks.

When you need to apply

You apply if the room goes past a limit, for example a taller roof, or if someone will sleep in it. See garden annexe rules. In the Green Belt, the council uses chapter 13 of the National Planning Policy Framework.

• Development is inappropriate unless it falls within a listed category. Inappropriate development is harmful and should not be approved except in very special circumstances.
• Harm to the Green Belt, including harm to openness, gets substantial weight. It must be clearly outweighed by other considerations.
• Extending or altering an existing building is not inappropriate if the building is of permanent and substantial construction and lawful, and the extension does not give a disproportionate increase in size over the original building.
• The essential features of the Green Belt are its openness and permanence.

How a council treats a garden room, as an extension to the house or as a new building, is a judgement for the council. Ask before you spend on drawings. This guide does not decide it for you.

What helps a Green Belt application

These are practical ideas, not rules.

• Keep the room modest and close to the house.
• Keep it single storey and low.
• Use materials that fit the setting.
• Do not add hard standing, tall fences or big lights.
• Ask the council for pre-application advice.

Green Belt in Herts and Bucks

Parts of both counties are in the Green Belt, and many of those areas are also in the Chilterns National Landscape or a conservation area. Edge-of-town and village plots are where you most need to check. This applies to places such as Harpenden, Chesham, Gerrards Cross and Kings Langley. We cannot say from the town name whether your plot is in it. Use your council's map.

Getting certainty

A lawful development certificate is a council decision on whether a proposed building is lawful. Anyone can apply. See our lawful development certificate guide.

Planning is separate from building regulations. See building regulations for garden rooms. For prices, use the garden room cost calculator and how a price is built. Room types: garden offices, garden gyms.

Common mistakes

• Assuming Green Belt means no. The outbuilding guidance does not list it as tighter land.
• Assuming Green Belt means yes. If you need permission, policy sets a higher bar.
• Overlooking other designations. Your plot may also be in a conservation area or the Chilterns National Landscape.
• Building a bedroom. A room someone sleeps in falls outside permitted development whatever the land.
• Paying for drawings before asking. Ask the council first.

Policy changes. The framework we read is the current one on GOV.UK at the date below. Your council applies it to your plot.