Where the electrician fits in your extension... get the order wrong and your plasterer's stood waiting

Most of the electrical jobs that go sideways on an extension aren't wiring problems. They're diary problems. The cable's fine, the board's fine... but nobody slotted the electrician into the programme at the right moment, and now the plasterer's on site with nowhere to plaster because the walls are still open and the cables aren't run.

If you're the one running the job... builder, project manager, or homeowner holding it together... this is the bit worth getting right early. Here's how the electrics slot into the build.

First fix and second fix... what they are

Electrical work on a new-build space splits into two visits, and they sit at opposite ends of the programme.

First fix is everything that has to happen while the walls and ceilings are open: chasing out channels for cables, running the cables back to the board, dropping in the back boxes for sockets and switches, and setting the points for lights. No visible fittings go on... it's all the stuff that's about to disappear behind plasterboard and skim.

Second fix is the visible half, and it comes right at the end: fitting the sockets, switches, light fittings and accessories, connecting it all up at the board, then testing and certifying. That happens after the decorator, not before.

The order that keeps everyone working

The sequence that matters most is a short one:

First fix goes in before the plasterer. Cables run, boxes set, chases cut... then the plasterer boards and skims over the lot.
Second fix comes after decoration. Walls painted, then I fit the accessories onto clean, finished surfaces.

Get first fix in the wrong side of the plasterer and you've got two bad options: hack open fresh plaster to run cables, or leave the plasterer standing idle while the electrician catches up. On a tight programme, a day of idle trades is real money, and it ripples down the whole schedule.

A Maidenhead example

I see this most on the 1930s semis around Maidenhead that are getting a rear extension... often as part of a bigger renovation now the Elizabeth line has made the commute painless. The pattern's always the same: knock through, extend, replaster half the ground floor, redecorate throughout.

The jobs that run smooth are the ones where I'm booked into the programme early, so I hit the chase-and-first-fix slot in the window before the plasterer arrives. The ones that stumble are where the electrician's an afterthought, called once the plastering's already booked... and then it's a scramble. Same trades, same house; the only difference is the order.

What I'll actually promise you

I book to your programme, not mine. That means:

I hit the first-fix slot before the plasterer, so the walls close on schedule.
I make good my own chases... I fill the channels I cut, so your plasterer's skimming a flat wall, not patching my mess.
I come back for second fix after the decorator, and fit onto finished surfaces.
New circuits in an extension are notifiable building work, so I certify and notify the work under the Part P competent-person scheme... one less thing for you to chase Building Control about.

If the extension's turning into a bigger job (a new consumer unit, or the existing wiring's tired enough that a full rewire makes more sense than patching in) that's worth flagging at the planning stage too, not mid-build. Same with the lighting: decide the downlights, wall lights and switch positions before first fix, because that's when they're cheap to move. Once it's plastered, moving a light means opening the ceiling back up.

Getting me in the diary

The best time to call me about an extension is before the walls go up, not after they've been plastered. Tell me the programme and I'll tell you honestly where I need to slot in.

I'm a NAPIT-registered electrician based in Slough, covering Maidenhead, Windsor and across the Thames Valley. For a free, no-obligation quote, and a straight answer on sequencing, get in touch at bphelectrics.co.uk and I'll fit around your build.