Garden Room Electrical Setup: A DIY First Fix Guide

Planning the electrics for your garden room is one of those stages that feels daunting at first, but once you understand the basics, it all starts to make a lot more sense. I’ve personally completed the first fix electrical installations on several garden rooms, running cables, positioning back boxes, planning circuits, before bringing in a qualified electrician to complete the installation and sign everything off.

That’s an important point to make upfront: I am not a qualified electrician, and neither are most self-builders. The final connection of your garden room electrics to the mains supply must be carried out by a Part P registered electrician who can certify the work. But there’s still plenty you can plan and prepare yourself, and understanding how it all works will save you time, money, and a lot of head-scratching.

Let’s get into it.

Table of Contents

Table of Contents
Do You Need an Electrician for a Garden Room?
Planning Your Power Load
Getting Power from the House to the Garden Room
Armoured Cable: What to Use and How to Run It
First Fix Electrics: What You Can Do Yourself
Cable Runs Inside the Garden Room
Power Sockets: Loop or Radial Circuit?
Lighting Circuits
Working Around Insulation and Downlights
Materials List
Cost Guide: Materials and Electrician Fees
Electrical Safety Requirements
When to Call a Professional
Build Your Own Garden Room

Do You Need an Electrician for a Garden Room?
Planning Your Power Load
Getting Power from the House to the Garden Room
Armoured Cable: What to Use and How to Run It
First Fix Electrics: What You Can Do Yourself
Cable Runs Inside the Garden Room
Power Sockets: Loop or Radial Circuit?
Lighting Circuits
Working Around Insulation and Downlights
Materials List
Cost Guide: Materials and Electrician Fees
Electrical Safety Requirements
When to Call a Professional

Do You Need an Electrician for a Garden Room?

Yes. For the final connection and certification. Under Part P of the Building Regulations, any new electrical installation that connects to the mains supply must be certified by a registered competent person. That means a qualified electrician needs to:

Install or connect the consumer unit (fuse board) in the garden room
Connect the armoured cable supply from the house
Test and certify the complete installation

What you can do yourself is the first fix: running cables, fitting back boxes for sockets and switches, and installing light fittings where no live connection is made. This is exactly what I do on my own builds, and it makes the electrician’s job faster, which saves you money on labour.

Planning Your Power Load

Before you start buying cable, think about what you’ll actually be using the garden room for. The power demand of a home office is very different from a workshop with power tools.

Here are some typical loads to consider:

Use Case	Estimated Load
Home office (computer, monitor, lighting)	500W–1,500W
Garden gym (treadmill, lighting)	1,500W–3,000W
Workshop (power tools, compressor)	2,000W–5,000W
Music studio or hobby room	500W–2,000W
Garden room with electric heating	1,500W–4,000W

As a rule of thumb, plan for a 32A supply if you want any form of electric heating or high-powered equipment. For a basic home office or hobby room, a 20A supply is often sufficient, but going larger gives you flexibility for the future. My own garden room, which I use as a music mixing and editing suite, runs on a 32A supply and with studio monitors, a PC, outboard gear, and lighting, it’s the right call.

Getting Power from the House to the Garden Room

This is the part most people are unsure about. Power needs to travel from your main consumer unit in the house out to a sub-consumer unit in the garden room. There are two main route options:

Option 1: Buried Underground (Recommended)

The cleanest and most permanent solution is to bury armoured cable underground from the house to the garden room. This is what I’ve done on most builds. You’ll need to dig a trench at least 500mm deep (deeper under driveways and areas of heavy traffic, 750mm is recommended under lawns or flower beds according to BS 7671 wiring regulations).

Digging trench for running armoured cable to garden room

The cable should be laid in the trench, covered with cable warning tape, then backfilled. This keeps it safe, tidy, and permanent.

Option 2: Running Along a Fence Line

Where digging a trench isn’t practical, perhaps because of a concrete path, large tree roots, or a complicated garden layout, the cable can be run along a fence line, attached at height using cable cleats or conduit. This is a valid option and one I’ve used before. It’s not as visually clean, but it’s practical and perfectly acceptable when done properly.

Running an armoured cable along a fence line

Armoured Cable: What to Use and How to Run It

For the outdoor run from house to garden room, you’ll need SWA (Steel Wire Armoured) cable. This is robust, weatherproof, and designed for direct burial or external use. Standard PVC cable is not suitable for this purpose.

Common SWA Cable Sizes

Cable Size	Suitable For
6mm² twin and earth SWA	Up to 40A, suits most garden rooms
10mm² twin and earth SWA	Higher loads, longer runs, or workshop use
16mm² twin and earth SWA	Very high loads or runs over 30–40 metres

For most garden rooms up to around 20–25 metres from the house, 6mm² SWA is the standard choice and will comfortably handle a 32A supply. If you’re running a longer distance or planning significant power loads, bump up to 10mm². Your electrician will advise on the correct size based on your planned load and run length. This is one area where it pays to get professional input before buying cable.

SWA cable terminates into a gland fitting at each end, which is then connected to the consumer unit inside and the house CU at the other end. This is work for your electrician.

First Fix Electrics: What You Can Do Yourself

First fix is the installation of all the cables, back boxes, and conduit before the walls are boarded and plastered. At this stage, nothing is live. You’re simply putting the infrastructure in place.

Here’s what I typically do myself on a garden room build before the electrician arrives:

Mark out socket and switch positions on the frame
Fit all back boxes (single, double, or deep boxes depending on use)
Run all internal cables from back box to back box and up to the consumer unit position
Pull cables through the wall or roof structure to reach light positions and ceiling connections
Leave sufficient cable tail at each position for the electrician to connect up
Mark or label each cable run to make the electrician’s job easier

This prep work can easily save two to three hours of electrician time, which at £50–£70 per hour is a meaningful saving.

Cable Runs Inside the Garden Room

Inside the garden room, you have a couple of routing options depending on your construction method:

Behind the Cladding

Running cables around garden room beneath cladding

On the builds I’ve done, I typically run internal cables on the exterior face of the timber frame, underneath where the cladding will be fixed. This keeps the cables completely hidden once the cladding is on, and avoids notching studs. The cables are protected by the cladding itself and clipped neatly to the frame. For this to work, you need to plan the cable routes before the cladding goes on. It’s much harder to retrofit.

Through the Frame (Notching or Drilling)

The alternative is to run cables through the stud frame by notching or drilling through studs and noggins. This is a standard approach in house building, but it takes longer and the cables need to be protected where they pass through timber. Nail plates are required over any notch within 50mm of the face of the timber to protect against accidental nail penetration.

Under the Floor

For socket runs along the base of walls, running cables under the floor and up through the sole plate can be a clean option, particularly if you have a raised timber floor with accessible void below.

Power Sockets: Loop or Radial Circuit?

This is a common question from first-time self-builders. In UK wiring, there are two main ways to wire a ring of sockets:

Ring Final Circuit (Loop): Cable leaves the consumer unit, visits each socket in sequence, then loops back to the CU. The ring allows current to flow in two directions, which means a 2.5mm² cable can safely serve more sockets than a radial. Traditional in UK domestic wiring.

Radial Circuit: Cable leaves the CU and visits sockets in a line, terminating at the last socket. Simpler to install. For garden rooms, a radial circuit is very commonly used. It’s straightforward, uses less cable, and is perfectly suitable for the loads involved.

For most garden rooms, a 20A radial circuit using 2.5mm² cable is the standard approach. If you’re planning heavy workshop use, a second circuit or a dedicated socket for high-draw equipment (like a compressor) makes sense.

My music studio garden room has separate circuits for power sockets and lighting, which is good practice and keeps any potential interference from lighting switches away from the audio equipment.

Lighting Circuits

Garden room lighting is typically wired as a radial lighting circuit from the sub-consumer unit, running to a switch position and then out to light fittings. This is simpler than a traditional loop-in ceiling rose setup.

The standard approach:

One 6A circuit for lighting (1mm² cable is sufficient for lighting)
Switch at the door position (single or double gang)
Cables running to each light fitting position

Indoor and outdoor lighting circuits explained

If you’re using recessed downlights, ceiling pendants, and external lighting, you might consider splitting into two separate lighting circuits for flexibility.

Working Around Insulation and Downlights

This is an area worth taking seriously. If you’re planning recessed downlights in the ceiling, there are a couple of important things to be aware of:

Fire risk from insulation contact: Standard recessed downlights can generate significant heat, and if insulation is packed directly over them in the roof void, there’s a real risk of overheating. You have two options: use fire-rated, insulation-covered (IC-rated) downlights that are designed to be buried in insulation, or install downlight covers above each fitting to create an air gap between the fitting and the insulation.

I always use IC-rated downlights or fit covers on garden room builds. It’s a small extra cost that removes the risk entirely.

Creating a recess for downlight installations in cold roof

Cable routing in a warm roof: If you’ve built a warm roof construction (see my Warm Roof vs Cold Roof guide for more on this), there’s an easily accessible roof void. For cold roof installations, cable runs need to work in and around the insulation. Planning this part is important for an effective cable run.

Plan your lighting layout before the ceiling goes in. Once it’s boarded, retrofitting downlights becomes a proper job.

Materials List

Here’s a typical materials list for a standard garden room electrical installation. Quantities will vary based on room size and layout.

External Supply

SWA armoured cable (6mm² twin and earth) – sold per metre, typically 15–30m for a garden run
SWA cable glands (2 off – one at each end)
Ducting/conduit for cable entry points
Cable warning tape for buried runs

Sub Consumer Unit

6-way (or larger) consumer unit with RCD protection
20A MCB for socket circuit
6A MCB for lighting circuit
Earthing rod or connection back to house earth

Internal Wiring

2.5mm² twin and earth cable (sockets) – sold per metre
1mm² twin and earth cable (lighting) – sold per metre
Back boxes: single (35mm depth) and double gang as required
Sockets and switch plates
Recessed downlights (IC-rated) or surface light fittings
Downlight covers if non-IC fittings used
Cable clips
Junction boxes
20A fused spur (for electric heater if required)

Cost Guide: Materials and Electrician Fees

Materials Costs (Approximate 2026 UK Prices)

Item	Approximate Cost
SWA cable 6mm² (per metre)	£3.50–£5.00/m
6-way consumer unit (RCD)	£60–£120
2.5mm² twin and earth (per metre)	£0.80–£1.20/m
1mm² twin and earth (per metre)	£0.50–£0.80/m
Back boxes and faceplates (full room set)	£40–£80
IC-rated downlights (per fitting)	£8–£20 each
Cable glands and conduit fittings	£15–£30
Cable clips, junction boxes, misc	£20–£40

For a typical 4m x 3m garden room, expect to spend £250–£450 on materials for the internal installation, plus the armoured cable supply run.

Electrician Fees

Labour costs vary by region, but as a rough guide for Cornwall and the South West:

Electrician day rate: £250–£400 per day
Typical garden room installation (first fix done): 1 day
Typical garden room installation (from scratch): 1.5–2 days
Certification and Building Regulations notification: £100–£200

Total electrician cost (if first fix is done): £350–£600 Total electrician cost (full installation): £600–£1,000+

Doing your own first fix prep and buying your own materials is one of the most effective ways to reduce the overall electrical cost of a garden room build. For a full breakdown of all garden room build costs, take a look at my garden room cost guide.

Electrical Safety Requirements

Whether you’re doing the first fix yourself or leaving everything to an electrician, there are some non-negotiable safety requirements for any garden room installation:

RCD protection: All circuits in a garden room must be RCD protected. A modern consumer unit with built-in RCD or RCBO protection on each circuit covers this.
Earthing: Proper earthing is critical. Your electrician will ensure the installation is correctly earthed, either via the house earth or a local earth rod.
Cable protection: Any cables that could be subject to mechanical damage must be protected, either by routing them in conduit or by using armoured cable externally.
Waterproofing at penetrations: Where cables enter the building, the penetration must be sealed to prevent water ingress.
Part P certification: As mentioned, any new electrical installation must be certified by a registered electrician. This also notifies your local building control, which matters when you come to sell the property.
Insurance implications: An uncertified electrical installation may invalidate your home insurance. Don’t skip the certification.

When to Call a Professional

To summarise what to leave to the professionals:

Connecting the armoured cable to your house consumer unit
Installing and connecting the garden room sub-consumer unit
Any live connection work
Testing and certifying the installation
Anything you’re not confident about

And what’s generally fine to tackle yourself with reasonable DIY competence:

Planning circuit layouts
Digging the trench and laying armoured cable (unconnected)
Running and clipping internal cables
Fitting back boxes
Installing light fittings (no live connections)
Fitting socket and switch faceplates once the installation is certified

Getting the electrics right is one of the most important parts of a garden room build, not just for safety, but because a properly certified installation adds genuine value to your property. If you’re building a garden room as a home office or studio, a solid electrical setup really is the foundation everything else sits on.

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Thanks for reading. Continue building your garden room construction knowledge with the other articles in this series, which together provide a complete and comprehensive guide to DIY garden room construction.