Electrical First Fix Checklist: What to Plan Before Your Extension or Loft Conversion

Once plastering starts on your extension or loft conversion, changing your mind about where a socket or light switch goes gets expensive fast. First fix is the stage where all of that gets decided — so it's worth planning properly before the electrician is even on site, not during.

What actually happens at first fix

First fix covers everything that needs to go in before the walls are closed up: cables run through joists and studwork, back boxes fitted for sockets and switches, and wiring routed for lighting, heating controls, alarms, and anything else electrical the room needs.

• Cable runs through walls, floors, and ceilings
• Back boxes for sockets, switches, and dimmers
• Wiring for lighting circuits, including any feature or under-unit lighting
• Heating control wiring, where relevant
• Data, TV aerial, and smart home cabling — much cheaper to include now than retrofit later

Loft conversions have their own rules

Building regulations are specific about loft conversions: mains-wired smoke alarms are required, with defined locations, and any extractor fan (for an en-suite, for example) needs to be wired in at first fix — not bolted on afterwards. Power points and lighting also need agreeing before plasterboard goes up, since retrofitting later means cutting into a finished ceiling.

Why timing with your builder matters

The single biggest cause of extra cost on extension electrics is being brought in too late — after first fix should have already happened. Ideally we're involved as soon as first fix is being scheduled, working directly from your architect's drawings or discussing the layout with your builder, so nothing gets missed and nothing needs re-cutting.

Certification and building control

Electrical work on an extension has to comply with Part P of the Building Regulations. Using a registered electrician (through NICEIC, for example) means the work can be self-certified, which saves you arranging a separate building control inspection for the electrics specifically. At the end of the job you should receive an Electrical Installation Certificate, a Building Control notification certificate, and full test results — keep all three with your property paperwork.