Start with the supply, not the sockets

It is tempting to plan a garden room by deciding where the sofa goes and then adding sockets around it. Resist that. The single biggest constraint on any garden building is how the electricity gets there, and that decision shapes everything else. Once you know whether you have a 13A spur, a 32A submain or a three-phase supply from a converted barn, you can plan the internal layout with confidence.

Almost every garden room in the UK is fed from the main consumer unit in the house via a submain. That cable leaves the house, crosses the garden, and terminates in a small consumer unit inside the building. Everything else – sockets, lights, heaters, that little wall-mounted fan – hangs off that second consumer unit.

Cable routes and the case for armoured cable

For anything buried, run steel wire armoured (SWA) cable. It is tough, it is designed for direct burial, and it gives you the mechanical protection that ordinary twin and earth simply does not. A grey PVC-sheathed flex buried in a flowerbed is an accident waiting to happen the first time someone puts a fork through it.

Burial depth matters. In a domestic garden, aim for at least 600mm of cover, with a warning tape or tile laid roughly 150mm above the cable so future diggers get a hint. If you cannot get that deep, consider a duct, or run the cable clipped along a fence or wall instead – but protect it from strimmers and ladders.

• Size the cable properly. A 4mm² or 6mm² three-core SWA is common for garden rooms, but voltage drop over long runs can force you up a size. A 40-metre run is a very different proposition from a 12-metre one.
• Include a separate earth core. Three-core SWA is easier to work with and avoids relying on the armour as the sole earth path, though the armour should still be properly glanded and earthed at the house end.
• Think about future load. If you might one day add a hot tub, an EV charger or a workshop heater, size the submain now. Digging the trench twice is miserable.

This is notifiable work in England and Wales, so use a registered electrician for the connection at both ends and get the certificate. Nobody enjoys paperwork, but nobody enjoys a house fire either.

Choosing the right consumer unit and circuits

Inside the garden room, fit a small consumer unit with an RCD or RCBO protection on every circuit. If the building is timber-framed, metal-clad or otherwise remote from the house earth, your electrician may recommend a TT arrangement with its own earth electrode rather than exporting the house earth. It is a technical call, and it depends on the earthing system at the property, but it is worth asking about early.

Most garden rooms can run happily on two circuits: one for socket outlets and one for lighting. Add a third for a dedicated heater, air conditioning unit or an outdoor socket on the exterior wall if you plan to use power tools outside. Keep the lighting circuit separate so a tripped socket does not plunge you into darkness.

Socket placement that actually works

Garden rooms are often built with a timber stud frame and a service void, which makes flush-mounted sockets straightforward. Plan them before the plasterboard or cladding goes on, because retrofitting is far more fiddly than it looks.

• Desk or workbench: a double socket either side, plus one above the worktop for a monitor, lamp or charger.
• Sofa or seating area: at least one double socket on each side, plus a USB-equipped outlet if you like a tidy floor.
• Media wall: four to six sockets behind the television, plus conduit for HDMI and network cables.
• Kitchenette or tea point: dedicated circuits for a kettle, microwave or small fridge if the room is used daily.
• Exterior: a weatherproof socket with an IP66 rating and a lockable cover, useful for mowers, lights and pressure washers.

Height-wise, 450mm to the centre is the familiar domestic standard, but in a garden room you can raise them to 900mm or higher if the walls are likely to be lined with tools or storage. Think about where furniture will sit so you are not crawling behind a sofa every time you need to charge a laptop.

Lighting that suits a garden room

Garden rooms are usually smaller than a living room but often do more jobs – office, gym, studio, guest space. Layering the light gives you flexibility without a huge electricity bill.

• Ambient light: LED panel lights or slim batten fittings give even, glare-free illumination and are ideal for a home office.
• Task light: under-cabinet LED strips over a desk or worktop, or an angled desk lamp on a socket circuit.
• Accent light: wall lights or a couple of dimmable pendants for evenings. Choose warm white (around 2700K) for relaxing and cool white (4000K) for working.
• Outside: a dusk-to-dawn security light or some well-placed path lights make the walk back to the house much friendlier in winter.

All of it should be LED. A garden room lit entirely with LEDs might draw under 50W, which means the lighting circuit is barely doing any work – leaving plenty of headroom on the submain for the things that actually pull current, like heaters and kettles.

Heating, ventilation and the load question

Heating is where garden room electrics quietly get serious. A 2kW fan heater pulls nearly 9A on its own, which is most of a 13A supply gone. If you plan to heat the building electrically, aim for a dedicated submain rather than a spur, and consider an air source heat pump or a low-wattage infrared panel instead of a resistive blow heater.

Ventilation matters too. A humidity-triggered extractor in a garden room used as a gym or utility space stops condensation forming on cold mornings, and it is far easier to install before the ceiling goes up.

Get the supply right, plan the sockets on paper, and choose lighting that flatters the space. Do that, and the wiring becomes the invisible part of the project – exactly as it should be.