Garden room electrics: what you need and what it costs

Electrics are the part of a garden room most people think about last and use most. Every time you switch on the heater, charge a laptop or turn on the lights on a dark afternoon, you are relying on decisions made in the first week of the build. They are cheap to get right at the start and expensive to change afterwards.

How power gets to the room

Almost every garden room is supplied the same way. A new circuit leaves the house’s consumer unit, protected by its own breaker and an RCD, and runs to the room in steel wire armoured (SWA) cable. The cable is buried in a trench, typically at least 450 to 600 mm deep under lawns and deeper under paths or drives, with warning tape laid above it. At the room it goes into a small consumer unit of its own, which feeds the sockets, lights and heating.

Three things decide the size and cost of that cable:

• Distance. Over long runs, voltage drops, so a room 30 metres away needs a thicker cable than one 10 metres away for the same load.
• Load. A room with a 1.5 kW heater, lights and a computer needs far less than one with an electric shower (8 to 10 kW) or an air-to-air heat pump and an oven.
• The house supply. Older houses, including many Victorian and Edwardian homes, may have a main fuse and consumer unit that cannot take a large extra load without an upgrade.

A good electrician works out the total load first, checks the house supply, and sizes the cable to suit. If there is any chance of a shower or kitchenette later, size the cable for it now; laying a second cable means digging the garden up again.

The rules: Part P

Installing a new circuit to an outbuilding is notifiable work under Part P of the building regulations in England. In practice that means one of two things:

1. A registered electrician (a member of a competent person scheme) does the work, tests it, and notifies building control on your behalf. You receive an Electrical Installation Certificate and, later, a building regulations compliance certificate.
2. Someone not registered does the work, and you apply to building control before it starts so they can inspect and test it. This is slower and usually costs more.

Almost every garden room builder uses a registered electrician, either in-house or a regular subcontractor. Ask for both certificates at the end and keep them with the house deeds; a buyer’s solicitor will want them.

Sockets, switches and lights

Plan the inside before the walls are lined, because adding sockets afterwards means opening up finished walls.

• Sockets: for an office, two double sockets at desk height (one with USB), one by the door, one for a heater, and one spare. For a gym or studio, spread them around the room. Floor sockets suit a desk in the middle of the room.
• Data: an armoured data cable laid in the same trench gives a wired connection as good as the house. Even if you plan to use Wi-Fi, it costs little to add while the trench is open.
• Lighting: a mix of downlights or a central fitting on a dimmer, plus a lamp or two, makes a room usable in the evening without feeling like an office.
• Outside: a light by the door on a sensor, and perhaps an outdoor socket for garden tools or a water feature.

Heating loads

Heating is where the electrics and running costs meet.

• Panel or oil-filled heaters of 1 to 2 kW are cheap to fit and fine in a well insulated room.
• Infrared panels on the ceiling or wall heat people and surfaces rather than air, and suit rooms used for short periods.
• Underfloor heating mats under the floor finish give even warmth and keep floors clear, at a higher fitting cost.
• Air-to-air heat pumps (air conditioning units) heat and cool, using roughly a third of the electricity of direct heaters for the same warmth.

At 2026 prices, a 1 kW heater running for eight hours uses 8 kWh, which costs roughly £2 at typical capped unit rates. In a properly insulated room it will cycle on and off, so actual costs are usually lower. Ofgem publishes the current cap on unit rates.

Typical costs

These are typical UK ranges for a garden room supply and fit-out, assuming the room is within about 20 metres of the house and the house supply is adequate:

Item	Typical cost
Armoured cable, trench and connection at the house	£600 to £1,500
Consumer unit, sockets, switches and lighting in the room	£600 to £1,500
Data cable in the same trench	£100 to £300
Outside light and socket	£150 to £400
Electric shower circuit (if needed)	£400 to £900 extra
House consumer unit upgrade (if needed)	£500 to £1,000

Most builders include a standard electrical package in the price of the room. Check what it covers: number of sockets, lights, heater, outside light, data cable.

Getting it right

Decide on the uses for the next ten years, not the next one. Tell the builder early if a shower, kitchenette, hot tub or electric car charger in the garden might ever come into it. Ask how far the room is from the house consumer unit and whether the supply needs an upgrade. And make sure the certificates arrive with the keys.

For a sense of how electrics fit into the wider budget, try the cost calculator, or read how an office is planned on our garden offices page.