First Fix

First fix (sometimes called “rough-in”) is the construction phase where all the hidden infrastructure goes in — the plumbing pipes, electrical cables, and structural carpentry that will be concealed behind walls, under floors, and above ceilings. It happens after demolition and structural work but before plastering.

What happens during first fix

Plumbing first fix

• Hot and cold water pipes run to all bathrooms, kitchen, and utility areas
• Waste pipes installed for sinks, toilets, showers, and baths
• Heating pipework laid for radiators or underfloor heating
• Gas pipes run to boiler, cooker, or fireplace locations

Electrical first fix

• Cables run through walls and ceilings to all socket, switch, and light positions
• Back boxes installed for sockets and switches
• Consumer unit (fuse board) wiring
• Data/network cabling if required
• Smoke and CO detector wiring

Carpentry first fix

• Stud walls erected to create new room layouts
• Door linings (frames) installed
• Floor joists repaired or reinforced
• Any structural timber work

Why first fix matters

First fix is one of the most critical phases because:

• Mistakes are costly to fix later — once the walls are plastered, accessing pipes and cables means ripping out the new plaster
• Decisions must be made now — you need to know exactly where every socket, light switch, radiator, and tap will go before first fix begins
• It sets the quality — good first fix work means reliable plumbing and electrics for years to come

Tips for homeowners

• Finalise your layout before first fix starts — moving a socket after plastering is expensive
• Walk the site with your electrician and plumber to confirm positions of everything
• Take photos of all pipes and cables before they’re covered — this is invaluable if you ever need to find them later
• Don’t rush — getting first fix right is far more important than getting it done quickly

Once first fix is complete and inspected, the walls are plastered, and the project moves to second fix.