Garage Conversion Electrics: Complete Electrical Guide UK 2026

• Part P (Electrical safety) — all new circuits, alterations to existing circuits, and consumer unit work are notifiable. A registered electrician self-certifies via their competent person scheme.
• Part L (Energy efficiency) — lighting must meet energy efficiency requirements. At least 75% of light fittings must be low-energy (LED). The insulation and heating design affects the electrical load calculation.
• Part B (Fire safety) — fire separation from the main house, interconnected smoke detection, and fire-stopping of cable penetrations. The electrician is responsible for the smoke detection and fire-stopping elements.
• Part F (Ventilation) — mechanical extract ventilation may be required, which needs an electrical supply. Factor this into the circuit design.

• Extend the house consumer unit — if the house CU has spare ways and the cable route to the garage is short, add new circuits directly from the house CU. This is the simplest and cheapest approach for basic conversions.
• Upgrade existing garage sub-panel — if the garage already has a sub-panel (common in integral garages), replace it with a modern RCBO board. Reuse the existing sub-main if it has adequate capacity for the new load.
• New sub-main and consumer unit — for high-demand conversions (kitchen, heating, EV charger), run a new sub-main from the house CU and install a dedicated consumer unit in the converted space. Size the sub-main for the total maximum demand.
• EV charger circuits — Section 722 — EV charging circuits are a special installation under BS 7671 Section 722. They require a dedicated circuit design (not simply a larger sub-main), a specific RCD type (Type A or Type B depending on the charger), and load management consideration where other high-demand circuits share the same supply. Use the cable sizing calculator to verify the circuit and sub-main design for the combined load.

Arc fault detection — Reg 421.1.7 (A4:2026)

BS 7671:2018+A4:2026 Reg 421.1.7 recommends the installation of arc fault detection devices (AFDDs) on AC final circuits to mitigate the risk of fire from arc fault currents. For a new garage conversion — particularly where the space will be used as a bedroom or home office — discuss AFDD provision with the client during the design stage. Where AFDDs are declined, note the recommendation on the EIC and record the client's decision. AFDDs fit in the consumer unit in place of standard MCBs or RCBOs and are available for 6 A, 10 A, 16 A, and 20 A circuit ratings.

• General lighting — LED downlights (6W to 10W each) are the standard choice. Space at approximately 1.2m centres for even coverage. A 5m x 3m garage typically needs 6 to 8 downlights for 300 lux at floor level.
• Task lighting — for home offices, provide additional lighting at desk positions (wall lights or under-cabinet strips). For kitchens, under-cabinet LED strips on the worktop circuits.
• Switching — switch at the entrance door. For bedrooms, provide two-way switching (door and bedside). For larger spaces, consider a dimmer circuit for comfort and energy saving.
• Part L compliance — at least 75% of fittings must be low-energy. With LED throughout, this is automatically satisfied.

• Electric panel heaters — simplest option. One or two wall-mounted panel heaters (1kW to 2kW each) on a dedicated radial circuit. Low installation cost but higher running cost than heat pumps or gas.
• Electric underfloor heating — popular in garage conversions because the floor is typically insulated and re-screeded as part of the structural work. Install heating mats or cables under the new floor finish. Requires a dedicated circuit (typically 16A to 20A) and a floor thermostat.
• Air source heat pump feed — if the conversion is substantial, a small air source heat pump may be specified by the M&E designer. The electrician provides the dedicated supply circuit (typically 20A to 32A) and the controls wiring.
• Mechanical extract ventilation — if the room has limited natural ventilation, a continuous or intermittent extract fan is needed. Wire from a fused spur (3A). For bathrooms or kitchens, link to the light switch with an overrun timer.

• Continuity of protective conductors on all new circuits
• Ring final circuit continuity (if ring circuits are used)
• Insulation resistance on all new circuits (500V DC, minimum 1 megohm)
• Polarity verification at every termination point
• Earth fault loop impedance (Zs) on every circuit
• RCD operation on all RCD/RCBO protected circuits
• Prospective fault current at the origin
• Functional testing of smoke alarms (interconnection, battery backup)

1. Site survey and design — assess the existing installation, determine consumer unit approach, design the circuit layout, and produce a quote.
2. First fix — run cables in walls, floor, and ceiling before plasterboard goes up. Install back boxes, cable routes for lighting, and any conduit for future services. Coordinate with the plasterer and insulation contractor.
3. Fire stopping — seal all cable penetrations through the fire-rated wall with intumescent sealant before plasterboard covers the openings.
4. Consumer unit work — install or modify the consumer unit. Connect the sub-main if applicable. Install MCBs/RCBOs for all new circuits.
5. Second fix — after plastering and decoration, fit switches, sockets, light fittings, and smoke alarms. Connect heating controls and extract fans.
6. Testing and certification — test all circuits, complete the EIC, and submit to the competent person scheme for Building Control notification.

• Bedroom / playroom — lighting, 4-6 sockets, heating circuit, smoke detection: £1,500 to £2,000.
• Home office — enhanced lighting, 6-8 sockets, data cabling, heating, dedicated circuits: £2,000 to £3,000.
• Kitchen / utility room — cooker circuit, multiple socket circuits, extract fan, lighting, heating, appliance circuits: £3,000 to £4,000.
• Add-ons — consumer unit upgrade at house: £300 to £500. New sub-main: £200 to £500. Underfloor heating: £400 to £800. Data cabling (Cat6): £80 to £150 per point.