First fix plumbing is the stage in bathroom installation (or any building project) where the hidden infrastructure of the plumbing system is installed—all the pipes, drains, water feeds, and waste outlets—before the walls are plastered, the tiles go on, or the shiny new fixtures are fitted.
Think of it as the skeleton or nervous system of your bathroom. You don’t see it once everything’s finished, but without it, nothing works.
When Does First Fix Plumbing Happen?
It usually happens right after the structural work is complete (like walls, floors, and framing) but before the finishing work (tiling, plastering, painting, and fitting toilets, sinks, and baths).
Timeline-wise:
- Stud walls built, floors open, and spaces accessible.
- Plumber runs all pipework: hot and cold water feeds, soil pipes, waste pipes, and any underfloor heating loops if included.
- Everything gets tested for leaks and correct positioning.
- Once signed off, the builders move on to the next stage: plastering, tiling, and preparing surfaces.
After that, you move to what’s called second fix plumbing (the fun part where taps, toilets, showers, and basins get connected).
What’s Included in First Fix Plumbing?
In a bathroom, first fix plumbing usually covers:
- Hot and cold water pipe runs for the bath, basin, shower, and toilet.
- Waste pipework (for sinks, baths, showers, and toilets).
- Soil stack connections (big pipes that carry waste water and sewage out of the house).
- Shower valves and concealed pipework for mixers or rainfall showers.
- Pipe chases in walls or under floors (grooves or channels cut to hide pipes).
- Stopcocks and isolating valves to control water flow.
- Heating connections if you’re having a heated towel rail or underfloor heating.
Basically, if it’s hidden behind tiles or walls, it’s part of the first fix.
Why Is First Fix Plumbing Important?
Because if this stage isn’t done properly, you’ll be facing expensive and messy fixes later. Imagine tiling your dream bathroom only to realize a pipe wasn’t fitted correctly—you’d have to rip tiles back off just to get to it.
That’s why first fix is all about precision and planning. The plumber has to know exactly where your toilet, shower, and sink will go—down to the millimeter—so the pipes are in the right spots when it’s time for the second fix.
A poorly done first fix can lead to:
- Leaks inside walls and floors.
- Poor water pressure in the shower.
- Incorrectly placed pipes (so your toilet or basin doesn’t align properly).
- Expensive rework once tiling or flooring is finished.
First Fix vs. Second Fix Plumbing
It helps to see the difference:
- First Fix: The invisible groundwork—pipes, wastes, drains, valves—everything hidden behind walls and under floors.
- Second Fix: The visible fittings—installing the toilet, connecting taps, fitting the bath, shower, and sink, sealing everything, and making it usable.
An easy way to remember it: First fix is what makes the water arrive and leave. Second fix is what makes the bathroom look pretty and actually work.
Cost of First Fix Plumbing in a Bathroom
Costs vary depending on your location, bathroom size, and complexity, but here’s a ballpark idea:
- In the U.K., first fix plumbing in a standard bathroom can cost £1,000–£2,500.
- In the U.S., for a new bathroom, first fix pipework typically runs $1,500–$5,000.
Factors that affect the price:
- Moving or relocating a toilet or bath (soil pipe work is pricier).
- Installing concealed showers or wall-hung toilets (requires more pipework).
- Whether it’s a new build (easier) or retrofitting an old bathroom (harder).
My Personal Take
When I renovated my bathroom, my plumber insisted on walking me through every fixture’s final position before starting first fix. At first, I thought he was just dragging things out. But later, I realized why: the tiniest detail—like whether you want your sink 2 inches higher, or your shower valve on the left instead of the right—affects the pipe layout.
If I hadn’t checked, I’d have ended up with a towel rail in the wrong place and a shower valve that would have been awkward to reach. Lesson learned: plan twice, pipe once.
Key Takeaway
First fix plumbing is the behind-the-scenes stage where all your bathroom’s essential pipework is installed before the finishing surfaces go in. It’s crucial because mistakes at this stage mean major headaches later.
So, if you’re planning a new bathroom, take your time here: decide exactly where everything goes, double-check measurements, and make sure your plumber tests everything before tiling begins. It’s not the glamorous part, but it’s the foundation of a bathroom that works perfectly for years.