Broadband, power and IT for a serious garden office

Nobody buys a garden office because they want to think about electrical spec or Ethernet cabling. But almost every complaint we hear from clients twelve months after handover — from any builder, not just ours — traces back to something in the invisible infrastructure. The building was fine. The 2.5 mm supply cable wasn't. The WiFi from the house's router in the front lounge didn't reach the desk. There was no dedicated circuit for the heat pump. This is the working brief we include as standard, and it's why our clients don't call twelve months in.

The supply — from the house to the room

The single most common under-spec we see is the supply cable. A garden office running a workstation, twin monitors, a heat pump, LED lighting, a heated towel rail and (occasionally) a kettle draws 3.5-4.5 kW at peak. That's roughly 15-19 A. A standard 2.5 mm SWA supply is fine for it. A 1.5 mm supply — which some builders use to save cost — sits on the ragged edge and trips its breaker under heat-pump load in February.

Our default supply:

• — 016 mm SWA (steel wire armoured) cable, direct-buried at 500 mm minimum depth, sand-bedded, marker tape at 250 mm.
• — 0220 A radial from a dedicated RCBO at the house consumer unit. Total supply length up to 40 m — beyond that we upgrade to 10 mm.
• — 03NICEIC-certified install with an EIC (Electrical Installation Certificate) at handover.
• — 04Isolator switch inside the garden room, so the supply can be dead-worked without needing access to the house.

The sub-consumer unit — the detail nobody quotes for

Every serious garden office needs its own sub-consumer unit inside the room. Not for regulatory reasons (a single radial is legal), but because separating the room's circuits means a single fault doesn't take the whole building down. Standard sub-consumer unit spec:

• — 016-way sub-consumer unit, dual RCD protection.
• — 02Circuit 1: Lighting ring (6 A) — LED downlights, task track, accent strip.
• — 03Circuit 2: General sockets ring (20 A) — desk sockets, kettle, phone charger.
• — 04Circuit 3: Heat pump dedicated (20 A) — must be its own circuit, most heat pumps require it.
• — 05Circuit 4: External sockets and lighting (16 A) — exterior wash, garden bar sockets, pergola lights.
• — 06Circuit 5: Spare — sized for a future EV charger or workshop equipment.
• — 07Circuit 6: Spare — reserved for AV or IT infrastructure upgrades.

Internet — the reality

Extending the house's WiFi into the garden is almost never good enough for a serious home office. Standard 5 GHz WiFi drops off sharply through two brick walls and 15 m of garden. Even 6 GHz WiFi struggles. The right answer is a wired backhaul.

Every Arden & Oak office quote includes:

• — 01Buried 32 mm Cat6-rated conduit from the house, direct-buried at 400 mm depth, up to 30 m included. Beyond that we quote per metre.
• — 02Cat6 or Cat6a cable pulled through — gigabit-capable, PoE-capable for a hardware access point.
• — 03Wall-mounted network access point (Ubiquiti U6-Mesh or equivalent, £180 supplied and fitted). Delivers full gigabit at the desk with roughly 400-600 Mbps sustained WiFi in the room.
• — 04Optional patch panel and small managed switch (£320 supplied) for clients running multiple hardwired devices — desk PC, VoIP phone, NAS.

The desk-height detail

The other small detail that matters — every desk-position in every office we build gets a coordinated wall-plate at desk height (roughly 780 mm from floor). Cat6 outlet, two 13 A sockets, one USB-A + one USB-C fast-charge socket. The desk sits against a wall that's already ready for it.

“Half of the 'my garden office isn't working' calls we take turn out to be someone else's WiFi problem. If you're building an office to work from, the wired backhaul isn't optional.”

— Arden & Oak — install team

What it costs

The full infrastructure spec above — 6 mm SWA supply up to 40 m, 6-way sub-consumer unit with 4 populated circuits, Cat6 duct + cable up to 30 m, PoE access point, coordinated desk-height wall-plates — sits at £1,850-2,400 all-in. Included as standard in our office quotes. Not an upgrade.

For the wider home-office brief see the South Devon office guide. For the tax and business-use conversation, see the garden-office tax article.