Garage and outdoor electrics: what it costs to run power outside

Running power to a garage, shed or garden office typically costs £400–£900 for lighting and a socket or two on a short run, and £600–£2,500 for a fuller installation with its own small board. It is notifiable work under Part P. And the thing that decides which end of that range you land on is not the outbuilding at all — it is what is already in your consumer unit.

What it costs in 2026

Published UK figures, checked September 2026, for a domestic outbuilding supply:

Yes, it is notifiable

Part P of the Building Regulations covers fixed electrical installations in dwellings in England and Wales, and it explicitly reaches outbuildings — detached garages, sheds, greenhouses. A new supply to an outbuilding is a new circuit, and new circuits are notifiable. In practice:

• Registered electrician — they self-certify the work and notify Building Control for you, and the certificate arrives with you. This is the normal route.
• Unregistered electrician — you must apply to Building Control before the work starts, and pay their inspection fee. Doing it afterwards is a regularisation application, which is more expensive and more awkward.
• Nobody notified — the missing certificate turns up in the searches when you sell, and an indemnity policy or retrospective application becomes the buyer's solicitor's problem, which means it becomes yours.

More detail on which jobs fall inside and outside the rules: Part P — what is notifiable.

The burial-depth claim everyone gets slightly wrong

Search this subject and you will be told the cable "must be buried at 500 mm". BS 7671 does not prescribe a depth. Regulation 522.8.10 requires buried cable to be of a construction suitable for the conditions, buried at sufficient depth to avoid damage from reasonably foreseeable disturbance of the ground, and marked by cable covers or marking tape. Depth is a design decision about your ground, not a number copied off a website.

Common domestic practice for steel wire armoured cable across a lawn is around 500 mm below finished ground level, bedded on and covered with fine sand or sifted soil so no sharp stone sits against the sheath, with yellow-and-black warning tape laid above the cable and below the surface. That is a reasonable default for a lawn. It is not sufficient where the ground will be disturbed more aggressively:

Ask for the route to be photographed and measured before it is backfilled. In ten years, when you are putting in a fence post, that photograph is the most valuable part of the job.

What a proper outbuilding supply includes

• Armoured cable sized for the load and the run length — voltage drop over 30 m is a real constraint, not a formality.
• A means of isolation at the outbuilding, so the supply can be switched off out there.
• A small consumer unit in the outbuilding where there is more than a single circuit, with its own overcurrent and RCD protection.
• RCD protection for socket-outlets intended to supply equipment used outdoors.
• Weatherproof accessories — enclosures rated for water and dust ingress, not indoor fittings in a plastic box.
• Earthing arrangements considered for the outbuilding specifically, which is a design question and one reason this is not a DIY job.
• A certificate, and Building Control notified.

Garden office, workshop, hot tub — load first

A light and a phone charger is a lighting-scale job. A garden office with electric heating, a workshop with a table saw, or a hot tub, is a load job, and it has to start with the arithmetic rather than the cable. A hot tub in particular can draw more than the rest of the outbuilding put together and is one of the few domestic additions that genuinely can exhaust the capacity of an older board. If the load calculation says the existing supply cannot carry it, the answer is not a thicker cable to the shed — see consumer unit replacement, and for equipment used out there, PAT testing.

Before you get quotes

1. Photograph the inside of your consumer unit — spare ways, and how old it is.
2. Measure the run from the board to the outbuilding, following the route the cable would take, not the straight line.
3. List the actual load: lights, sockets, heating, machinery, hot tub.
4. Say what the cable crosses — lawn, driveway, patio, borders.
5. Confirm the certificate and Part P notification are in the price.
6. Check the contractor on the Registered Competent Person Electrical register before booking.

If the existing installation is old enough that you are unsure what state the circuits are in, an EICR before the work is cheaper than discovering it halfway through, and a quote for the outbuilding will be firmer for it.