Garden Room Electrics: What You Need

A garden room needs the same basic electrical infrastructure as any habitable space: a properly protected supply from the house, a local consumer unit, and circuits sized for the loads you plan to run. Doing this correctly requires Part P notification and specific equipment choices that differ from standard indoor wiring.

How the supply runs from the house

The cable between the house and the garden room must be steel wire armoured (SWA) cable. SWA cable has a metal outer layer that protects it against garden tools, ground movement, and accidental damage. Standard domestic cable is not suitable for outdoor or underground runs.

The cable can be routed in two ways. Overhead between the buildings is possible for short spans if the cable can be maintained at a safe height. More commonly, the cable is buried underground in a duct (a plastic conduit that protects the cable and makes future replacement straightforward). The trench should be at least 500mm deep under cultivated ground and 600mm under a path or driveway. Paving and ground reinstatement are part of the job.

The cable terminates at an isolation point in the house, usually the consumer unit, and at a small consumer unit inside the garden room.

What goes inside the garden room

A consumer unit inside the garden room allows you to isolate power to the structure from inside it and provides individual protection for each circuit. Typical circuits include a ring final or radial circuit for sockets, a lighting circuit, and a dedicated circuit if you are running a heat pump, air conditioning unit, or workshop machinery.

All circuits inside the garden room should have RCD protection. A standard all-RCBO consumer unit handles this cleanly, with each circuit independently protected.

How the supply is sized

The total current demand from the garden room determines the cable size needed from the house. For a standard garden room with lighting, a few sockets, and a small heater, a 32-amp supply is usually sufficient. If you plan to install a hot tub, a large workshop machine, or a heat pump, the supply cable and protective device need to be sized to match.

Getting the cable size right at installation is important. Uprating it later means excavating the trench again.

Part P requirements

Installing a new circuit to a garden structure is notifiable work under Part P Building Regulations. A registered electrician self-certifies the work and issues a Part P completion certificate. That certificate matters for insurance purposes and at the point of property sale.

Planning permission

Planning permission is not generally required for the electrical supply itself, but the garden room structure may require planning consent depending on its size, position, and the rules set by your local planning authority. That is a separate consideration from the electrical work, and worth confirming before you start.