Garden rooms in conservation areas and the Chilterns

Designated land

Government guidance calls conservation areas, National Parks, Areas of Outstanding Natural Beauty (AONBs), World Heritage Sites and the Broads "Article 2(3) land". On this land, permitted development gives you less room. The Planning Portal says rights are more restricted, so some work that needs no application elsewhere will need one.

• Conservation areas. An outbuilding between the side wall of the house and the boundary needs planning permission.
• National Landscapes (AONB). The side-wall rule applies. Anything more than 20 m from the house is limited to 10 m² in total. The Chilterns National Landscape covers parts of both Hertfordshire and Buckinghamshire, so check whether your address is inside it.
• Listed buildings. Any outbuilding within the grounds of a listed building needs planning permission.
• Flats and maisonettes. These permitted development rights do not apply.
• Article 4 directions and old conditions. A council can remove permitted development rights in an area, or a past planning condition can remove them for one house.

The main outbuilding rules are in our planning permission guide.

Conservation areas

In a conservation area, an outbuilding cannot be placed on land between a side wall of the house and the boundary without planning permission. St Albans City and District Council states the same rule on its outbuildings page.

That leaves the back garden. A room behind the house, with the usual height and size limits, can still be permitted development. But there are two extra points.

• Article 4 directions. A council can make a direction that takes away permitted development rights in part of a conservation area. The Planning Portal says they are made when the character of an area of acknowledged importance would be threatened. Ask the council if one covers you.
• Looks. Even where you do not need permission, a sympathetic design and materials are a good idea. If you do apply, the council weighs the effect on the character of the area. See garden room cladding.

Much of Berkhamsted is in a conservation area. Check your own address on the Dacorum Borough Council planning maps. Other towns we cover, such as St Albans, Amersham and Beaconsfield, may also have conservation areas, so check rather than assume.

The Chilterns National Landscape

The Chilterns Conservation Board describes National Landscapes as designated areas of outstanding natural beauty (AONBs). Special planning controls apply. It says the Chilterns area is split across nine local planning authorities: two county councils, four district councils and three unitary authorities. Parts of Hertfordshire and Buckinghamshire are inside it.

What it means for a garden room

• Permitted development still exists, but with two limits: the side-of-house rule, and a total of 10 m² for any building more than 20 m from the house.
• If you need planning permission, the council weighs the effect on the landscape. Buckinghamshire Council says it will not permit development that would cause unacceptable harm to the area's natural beauty, and it encourages use of its Planning Advice Service.
• Significant proposals in or near the area may need a landscape and visual impact assessment. A garden room is not normally that large, but ask the council.
• Lighting can matter. The Board publishes lighting guidance to protect the Chilterns dark skies. Keep outside lights low and shielded.

The Board also publishes guidance for householders, including the Chilterns Buildings Design Guide. Read it before you pick a design.

Towns with land in or next to the area include Chesham, Great Missenden, Tring and Northchurch. Check each address, since the boundary runs through towns.

Listed buildings

Any outbuilding in the grounds of a listed building needs planning permission. If your home is listed, start with the council.

How to check

• Look up your address on your council's conservation area and planning maps.
• Ask the planning team whether an Article 4 direction applies.
• For certainty, apply for a lawful development certificate. See our lawful development certificate guide.
• Ask builders if they have worked in your area.

Green Belt is a separate matter. See garden rooms and Green Belt. For the design side, the garden office and garden studio pages show typical rooms. For costs, use the garden room cost calculator and read how a price is built.

Common mistakes

• Assuming the town name decides it. Boundaries run through streets. Check the address.
• Forgetting the side-garden rule. A room beside the house, between the side wall and the boundary, needs permission on this land.
• Ignoring old conditions. A past planning condition can remove permitted development for one house.
• Building a long way from the house. In a National Landscape, buildings more than 20 m from the house share a 10 m² total.
• Skipping a conversation with the council. A short call can save weeks later.

Protected land does not mean no. It means you check first.