We do not publish a flat price per square metre, because two extensions of the same size can be very different jobs. What follows is the honest list of things that move the number, so you can read competing quotes properly and see where they differ. Ask for a free written quote once your layout is settled and you will get a figure specific to your build rather than an average.
The main cost drivers
Circuit count comes first. A single storey rear extension with a kitchen in it needs far more than a bedroom over a garage.
- How many new circuits are needed and how far they run from the board
- Whether the existing consumer unit has spare ways and enough capacity
- Lighting design: quantity of points, dimming, switching and any feature circuits
- Kitchen content such as hob, oven, induction supplies and appliance spurs
- Underfloor heating, air conditioning or heat pump control wiring
- Access and structure, since steels, concrete and thin floor zones slow cable routes
- Testing, certification and notification of the notifiable work
First fix and second fix are separate visits
First fix is cabling and back boxes before plastering. Second fix is accessories, fittings and the board work after decoration is under way. Quotes should show both, because a price that only covers first fix will look cheaper and is not comparable.
How to compare quotes on the same terms
Ask each electrician for the same three things and the differences become obvious.
- A circuit by circuit list, not a single line for electrics
- Whether consumer unit work is included or provisional
- Whether testing, certification and notification are in the price
Where money is well spent
Extra sockets at first fix are cheap. Adding them later means chasing finished walls. The same goes for a spare cable pulled to a future EV charge point or garden supply while the trenches and voids are open.
Common questions
- Can you quote from drawings?
- We can give a good scope from drawings, then confirm on a short site visit once the shell is up.
- When should the electrician be booked?
- As soon as your build programme has dates. First fix has to land between joinery and plastering.
- Is the consumer unit always extra?
- No. If the existing board has spare capacity and passes testing it may not need changing at all.
- Do you charge for quotes?
- No. Quotes are free and given in writing.
Send your plans for a free written quote broken down by circuit, first fix and second fix.
Related guides
- Do I Need a New Consumer Unit for an ExtensionSometimes yes, often no. Testing answers it rather than guesswork.
- Wiring a Home ExtensionAn extension's electrics are only as good as the installation they connect to.
- What Electrical Work Needs Building Control Sign OffSome electrical work has to be notified to building control. Plenty does not.