Annexes and Granny Flats in London: Planning the Electrics

More London families are creating self-contained annexes: a granny flat over the garage, a converted outbuilding, or a separate unit in a large garden for a relative, an adult child or a lodger. An annex usually has its own kitchen, bathroom and heating, so it needs much more than a socket run from the house. This guide covers the electrical points to plan for. It is general information, not legal or planning advice.

Supply from the house or a separate supply

Most annexes are fed from the main house through a dedicated cable to their own consumer unit. This works well if the house supply has spare capacity. If the annex will have electric heating, an electric shower and cooking, the total load can be high, and a separate supply and meter from the network operator may be the better option, especially if the annex will be let. A survey will check the main fuse, consumer unit and earthing first.

Inside the annex

• A small consumer unit with RCD protection for all circuits.
• Separate circuits for cooking, an electric shower and heating where needed.
• Enough sockets for a kitchen, living space and bedroom.
• Interlinked smoke and heat alarms, ideally linked to the house so a fire in one is heard in the other.
• Outdoor lighting on the path between the house and the annex.

Cable runs and outbuildings

If the annex is a separate building, the cable from the house should be a suitable armoured type, buried at a safe depth or protected along its route. Earthing arrangements for outbuildings need careful design. Our guide to garden rooms and hot tubs covers cable runs to the garden in more detail.

Planning and Building Regulations

Creating an annex usually needs planning permission and Building Regulations approval, and the electrical work is notifiable. Keep the Electrical Installation Certificate and completion paperwork. If the annex is created inside the house, see our guides to loft conversion electrics and extension electrics.

If you rent it out

If the annex is let to a tenant, the landlord electrical safety rules for private rented homes in England may apply, including a satisfactory EICR at least every five years. Check whether your arrangement counts as a tenancy.

Book a survey

Energy North Ltd wires and inspects annexes and outbuildings across North, East and West London with City & Guilds certified electricians. EICR from £100. See our EICR service.