Loft Conversion Electrical Wiring London — Part P Compliance

A loft conversion involves adding new circuits — typically lighting, sockets, smoke alarm, possibly an en-suite circuit. All notifiable under Part P of the Building Regulations.

Notification can be self-certified by a Competent Person Scheme contractor (NICEIC, NAPIT, Stroma) — saves you the Building Control application fee but doesn't skip the compliance.

An EIC (Electrical Installation Certificate) must be issued for the new work. This sits alongside any existing EICR — the EIC is for the new work, EICR is the periodic condition report of the whole installation.

Building Regulations Approved Document B requires interlinked smoke alarms on every storey of multi-storey domestic properties. A loft conversion adds a storey.

Smoke alarms in the new loft room (heat alarm if it's a kitchenette, smoke alarm otherwise) must be wired (mains-powered with battery backup) and linked to the existing system.

Two interlinking methods: hard-wired (CAT5 or similar between alarms) or RF-linked (wireless modules on each alarm). RF is easier in retrofit; hard-wired is more reliable.

Cost: £80-150 per alarm head + £200-350 install labour for a typical 3-alarm interlinked system.

Lighting circuit — typically 6A radial via 1.5mm² cable. Sufficient for LED lighting and any wall lights.

Sockets circuit — 32A ring or 20A radial depending on load. 4-6 sockets in a master bedroom loft is typical.

En-suite circuit (if applicable) — separate radial for shower, hand dryer, towel rail.

Smoke/heat alarm circuit — interlinked with existing system.

Optional: CAT6 for home office use (smart TV, work setup), HDMI/AV runs for entertainment.

Older fuse boards (pre-2008) may not have spare ways for the new circuits. Upgrade typically required as part of the conversion.

Modern boards (12-way Hager etc.) often have 2-4 spare ways. Sufficient for a typical loft conversion if no en-suite.

If an en-suite is included, plan for a fuse board upgrade — 3-4 new circuits is often more than spare capacity.

Cost: fuse board upgrade £700-1,100 for a 12-way Type A RCBO board. Worth doing alongside loft wiring rather than as a separate visit.

Bedroom only (no en-suite): £1,800-2,800 including new circuits, smoke alarm interlinking, EIC, certification, and minor consumer unit updates.

Bedroom + en-suite: £2,800-4,200 including the above plus en-suite circuits, shower install, and any bathroom-zone-compliant fittings.

Master suite with home office: £3,500-5,500 including CAT6 networking, AV pre-wire, and additional sockets.

Add £600-1,100 if a full fuse board upgrade is needed.

Add £400-700 for any additional circuits to the rest of the property triggered by the loft work (e.g. additional ring main in the room below).

Electrical first-fix happens after the carpenter has framed the new walls and roof structure. Typically week 4-6 of a 12-week loft conversion.

Electrical second-fix happens after plastering and before decoration. Typically week 9-10.

Smoke alarm install and EIC commissioning is the last electrical job. Typically week 11-12.

Building Control inspection should happen after second-fix and before plaster — they need to see the new circuits in conduit/chased before walls are made good.

Co-ordinate with the main contractor's schedule. Last-minute electrician bookings around loft completion are 30-50% more expensive.