Garden Room Electrics Costs UK 2026 — What to Charge to Supply Power to an Outbuilding

What the Job Actually Involves

On the surface a customer thinks they want "a couple of sockets and a light in the shed." In reality, supplying power to an outbuilding is a notifiable electrical job with several distinct elements, each of which carries cost and risk. Pricing it as a single round number without understanding the parts is how operators lose money.

The core of the work is running a steel wire armoured (SWA) cable from the house consumer unit out to the garden room. That feed terminates into a small consumer unit or sub-board inside the outbuilding, which then distributes to the sockets, lighting, heating and data inside. Get the cable, the route and the board right and the rest is straightforward second-fix work.

The SWA Cable Run

SWA cable is the standard choice for an outdoor supply because its steel armour gives mechanical protection and can act as the circuit protective conductor. The cable is run from a dedicated way in the house board, out through the wall, along or under the route to the outbuilding, and into the sub-board. The two big variables are the length of the run and how it's installed — buried in a trench, clipped along a wall, or slung overhead on a catenary wire.

Trenching is the most common method. The cable should be buried at a sufficient depth — typically a minimum of 450–600mm — and protected with warning tape and, in many cases, a duct or run of cable protection so a future spade or fork doesn't find it. Where a trench isn't practical — across an established lawn the customer won't let you dig, or over a hard yard — an overhead catenary run on a tensioned steel wire is an alternative, mounted high enough to clear vehicles and people.

Sizing the Cable for Load and Run Length

Cable size isn't a guess. It's driven by the load the outbuilding will draw and the length of the run, because voltage drop increases with distance. A 30m run feeding a home office with a couple of sockets and LED lighting is a very different calculation from a 60m run feeding a studio with electric heating and an oven. Undersize the cable and you get excessive voltage drop and a feed that won't carry the load; oversize it for no reason and you've eaten your margin on copper you didn't need.

• Short run, light load (office, lights and sockets): commonly 4mm² or 6mm² SWA
• Longer run or heavier load (heating, workshop): often 10mm² SWA or larger
• Voltage drop must stay within the limits in BS 7671 across the full run length

Always design to the load the customer actually wants now and allow sensible headroom for what they'll plug in later. A garden office that becomes a gym or a workshop a year later is a common scenario — building in a little spare capacity is cheaper than going back to dig the trench again.

At the House: The Dedicated Way

The supply needs a dedicated circuit in the house consumer unit, protected by an appropriately rated RCBO. If the existing board has a spare way and is in good condition, this is a quick addition. If the board is old, full, or non-compliant, you may need to fit a new way, an enclosure, or — in some cases — flag a board upgrade as a separate piece of work.

A consumer unit change is one of the biggest swing factors in a garden room quote. A modern board with a free way costs you almost nothing to add to; an old fuseboard with no RCD protection and no spare capacity can turn a £900 job into a £1,500+ job once the board is sorted. Inspect the existing board before you price — never assume there's a spare way.

At the Outbuilding: The Sub-Board and Circuits

Inside the garden room the SWA terminates into a small consumer unit (sub-board) with its own RCD protection. From there you wire the final circuits. A typical garden office build-out includes:

• Sockets: a ring or radial of double sockets, sized to how the room will be used
• Lighting: internal LED lighting plus, often, external lighting at the door
• Heating: an electric panel heater, infrared, or air-con unit on its own circuit
• Data: a hardwired network/data cable run alongside or separate from the power, as customers increasingly work from the room

The number of circuits is one of the strongest cost drivers. "A few sockets and a light" is one thing; sockets, two lighting circuits, a heating circuit, external lighting and a data run is a materially bigger job. Quote each element as a line so the customer can see what they're paying for — and so they can choose to add or drop circuits without you having to re-quote from scratch.

Part P, Notification and Certification

Supplying a new circuit to an outbuilding is notifiable work under Part P of the Building Regulations. It must be carried out by a competent person — either a registered electrician who can self-certify through a scheme such as NICEIC, NAPIT or ELECSA, or notified to building control before the work starts. This is not optional, and it is one of the things that separates a proper quote from a cash-in-hand "mate with a drill."

On completion the customer should receive an Electrical Installation Certificate (EIC) covering the new supply and circuits, along with the building regulations compliance certificate from your scheme. Make this part of your pitch: the certification protects the homeowner at resale, satisfies their insurer, and is something the unregistered competition can't provide. Build the admin time for testing and certification into your price — it's real work, not a free add-on.

Typical 2026 Price Bands

Prices vary by region, run length, ground conditions and the number of circuits, but the following bands reflect what most domestic electricians are charging in 2026 for supplying power to a garden room or outbuilding. These figures assume you, not a separate groundworker, handle a straightforward trench.

• Basic supply — short trenched SWA run, sub-board and a few sockets and lights: £800–£1,500
• Mid-range — longer run, higher load, more circuits (heating, data, external lights): £1,500–£3,000+
• Larger / complex — significant groundworks, very long cable runs, board upgrade, heavy load: £3,000 and up

The single biggest reason these bands are so wide is groundworks. The electrical work to a small office is fairly consistent; the cost of getting the cable from A to B across a particular garden is what moves the number. Price the route, not just the room.

Worked Examples

Example 1 — Simple home office, short run

A 4m x 3m garden office, 18m from the house, soft lawn the whole way. The customer wants four double sockets, internal LED lighting and an external light at the door. The house board is modern with a spare way.

• RCBO and dedicated way in existing board
• 18m of 6mm² SWA, trenched at 600mm with warning tape and ducting
• Small RCD sub-board, sockets, lighting and external light
• Testing, EIC and certification

Price: ~£1,100–£1,400. A clean run, no obstacles and an easy board addition keep this firmly in the basic band.

Example 2 — Studio with heating and data, longer run

A larger garden studio, 35m from the house, with a section of the run crossing a gravel path. The customer wants six sockets, two lighting circuits, a panel heater on its own circuit, a data cable for working from home and external lighting.

• RCBO and dedicated way; board has capacity but is older
• 35m of 10mm² SWA sized for the heating load and run length
• Trenching including the gravel-path crossing
• Sub-board with multiple ways, sockets, two lighting circuits, heating circuit, data run, external lights
• Testing, EIC and certification

Price: ~£2,200–£2,800. The extra circuits, the heavier cable and the longer trench push this into the mid band.

Example 3 — Long run, board upgrade and a driveway crossing

A workshop/studio 55m from the house at the far end of the garden. The cable route has to cross a block-paved driveway, and the existing fuseboard is an old unit with no spare way and no RCD protection — it needs replacing before the new supply can be added.

• Full consumer unit upgrade in the house
• 55m of larger SWA sized for the run length and load
• Groundworks: long trench plus lifting and reinstating a section of driveway (or a deeper duct under it)
• Sub-board, multiple circuits, heating, data and external lighting
• Testing, EIC and certification

Price: ~£3,500–£5,000+. The board upgrade and the driveway crossing are the swing factors — both are easy to underestimate if you price off a phone call instead of a site visit.

The Cost Drivers That Move the Number

Two outbuildings the same size can be hundreds of pounds apart. The variables below are what you check on site before you commit to a price.

• Cable run length and trenching: the longer the run, the more cable, the more digging and the larger the cable size needed for voltage drop. Trenching labour is often the biggest single line on the quote.
• Ground conditions and obstacles: a soft lawn is cheap to trench. Crossing a patio, a block-paved driveway or a concrete yard means lifting and reinstating — or moling/ducting underneath — and that adds significant cost and time.
• Load and number of circuits: "sockets and a light" versus heating, data, two lighting circuits and external lights is a materially different job in both cable size and labour.
• Board upgrade: if the house consumer unit has no spare way or no RCD protection, a board change can add £400–£700+ before you've run a metre of cable.
• Heating: electric heating is a real load that pushes cable sizing up and needs its own circuit — factor it into the design, not as an afterthought.
• Catenary vs trench: where digging isn't allowed, an overhead catenary run changes the method, the materials and the price.

Quoting Tips — What to Check Before You Price

Garden room electrics quotes go wrong when the electrician prices off the customer's description rather than a site visit. Before you commit a price, check the following:

• Walk the route: measure the run, identify every obstacle — patios, driveways, paths, drains, tree roots — and decide trench versus catenary before you quote.
• Inspect the board: confirm there's a spare way and RCD protection. If not, price the upgrade as a separate line.
• Establish the load: ask what the room is for now and likely later. Heating, a workshop or a kitchenette changes the cable size and the price.
• Confirm circuits: agree the number of socket, lighting, heating and data circuits in writing so there's no scope creep on the day.
• Reinstatement: if you're crossing hard surfaces, agree who lifts and relays them and price it explicitly.
• Certification: include testing, the EIC and building regs notification in the price — it's billable work and a selling point.

Quote each element as a separate line — supply cable and trenching, board work, sub-board, each circuit, certification. An itemised quote elevates you above the operator who just sends a round number, lets the customer add or drop circuits cleanly, and protects you when the scope changes.

Quick Reference: Garden Room Electrics Prices UK 2026