Adding a garden room and outdoor kitchen — do I need a separate sub-board or extend the main one?

Short answer: for a separate area with several circuits (lights, sockets, an AC, kitchen appliances) that's some distance from the house, the proper approach is usually a dedicated SUB-BOARD (sub-DB) fed by one correctly-sized, protected "submain" cable from the main board — not a tangle of long runs back to the main DB, and definitely not spurred off an existing socket. The sub-board gives that area its own MCBs/RCD protection locally, keeps voltage drop over the distance in check, and makes the whole thing safe, tidy and easy to isolate. You only extend the main board directly if it's close and just one or two circuits.

Why a sub-board is the right call here: - Several circuits + distance: running the garden room's lights, sockets, AC and kitchen individually all the way back to the main DB means lots of long cables and a main board that may not have the ways/MCBs spare. A single submain to a local sub-DB, which then splits into the local circuits, is cleaner and standard practice. - Voltage drop: over a long run, an undersized cable drops voltage (dim lights, struggling AC). A properly-sized submain to a nearby sub-board fixes that — the local circuits are then short. - Protection & isolation: the sub-DB has its own RCD/MCBs, so a fault in the garden room trips locally, and you can isolate that whole area without killing the house. Outdoor/wet areas need the right protection anyway.

Done properly: - Size the submain for the total new load AND the distance (this is where the main board's spare capacity from a load check matters — the new area's demand must fit). - Correct cable, protected and routed for an outdoor run (buried/ducted as needed), terminated into a proper enclosure. - Earthing/bonding done correctly for the new structure.

Common mistake: feeding a new outbuilding off the nearest outdoor socket or a skinny extension cable — overloaded, unprotected, and dangerous outdoors. Plan it as a submain-to-sub-board job with a licensed electrician to size and protect it, ideally before the building work so the cable route is built in. Anyone regret not putting a sub-board in an outbuilding?