Garden room london interior in Islington

What is a Garden Room?

A garden room tends to be a detached building, constructed within a garden. They can have many uses, most commonly as a home office or study, but can be tailored to your needs. See this example of a garden room we created in Barnet, London.

One of the benefits of a garden room is that they can often be built without seeking planning permission. This results in a relatively fast method of providing more space for your home. This journal post will explain the costs and constraints of building a garden room along with the rules you will need to follow in order to bypass planning, building under ‘permitted development’.

View Architecture for London’s portfolio of recent residential projects.

How much does a garden room cost?

The cost of a garden room will be dependent on its use and the level of finish you wish to apply to the building. If you plan to use the room in winter the building will need to be properly insulated with heating, ventilation and electricity.

Bespoke garden rooms tend to cost between £1,200 to £3,000 per square metre to build. This figure will depend on your location (materials and labour are more expensive in London compared to elsewhere in the UK). Other variables include the particular restrictions of your site and the intended purpose of the room (be it a dining room only to be used in summer or a year-round workspace).

It may be cheaper to purchase a pre-fabricated or modular design, but it is important to first establish the extra costs that may be involved. There might be additional transport costs – how far away is it pre-fabricated and do they include delivery? How constrained is your site? If you live in a typical Victorian terrace house, it is unlikely your garden has good access and the costs of craning the structure can add up.

Alternatively, you could have a bespoke garden room built. Although the construction cost and design fees may result in a more expensive project, it can be completely tailored to your needs, resulting in a more useful space.

Garden room islington architect

Extra Costs to Consider

Consultant Fees

The cost of professional services tends to be 15%-20% on top of the construction cost for this type of project. An architect is an invaluable tool in the design of your garden room. They can tailor the design to your specific needs, will be on hand for any advice and can produce detailed drawings so that you can receive accurate quotes from builders, avoiding unseen rises in costs. Additional specialist consultants may need to be involved in the project depending on the nature and location of the project.


You may be able to claim back the VAT on your garden room. This applies to those who are VAT registered and if the garden room has been built for the sole purpose of a workplace. If not currently registered for VAT, you can claim for VAT incurred in the previous 4 years.


If you need to apply for planning permission, this usually costs £206 to make an application (2018 figure). For further information, see our article on planning costs here. If building control approval is required there could be extra fees to take into account.


It is likely you will build your garden room a fair distance away from your house, so one of the larger expenses is having the building connected to mains electricity and testing the circuit. The further the garden room is from your property, the more this will cost. The electrician must be Part P registered and the electricity will be run through armoured cabling to be buried underground. You can expect this to cost between £850 – £1200.

Garden room interior

Do I need to get planning permission?

Permitted Development

A garden room can be built under ‘permitted development’ if the design follows the rules outlined below by the governments planning portal.

The building must sit behind the principal elevation (the street-facing elevation) of the original house (the house as it was first built or as it stood on 1 July 1948).

The room must not exceed 50% of the total area of land around the original house. Sheds, outbuildings and extensions (built after 1 July 1948) must also be taken into consideration in this calculation.

The garden room cannot exceed a single storey, with a maximum eaves height of 2.5m and overall height of 4m on a dual pitched roof, or 3m for any other roof. If the garden room is within two metres of a boundary, the maximum overall height is reduced to 2.5m.

You cannot construct a garden room without planning permission in the grounds of a listed building. In National Parks, AONB’s, Broads and World Heritage Sites, if the garden room is more than 20 metres from any wall it must not exceed 10 square metres.

Should you wish to construct a room that does not adhere to the above conditions, you will need to seek planning permission. The conditions above are not exhaustive, if you are unsure if your design falls under permitted development, seek further advice from an architect.

Building Control

If your design is less than 15 square meters and contains no sleeping accommodation, you will not normally need building control approval. The same applies to a garden room between 15-30 square metres. The above examples assume the room is at least 1m from any boundary and is constructed of non-combustible materials.

Further information

Please contact Architecture for London if you would like more details about garden rooms, or have queries in relation to a specific site. We would be happy to arrange a meeting with an architect to discuss your project in detail.