Walls or floor first

11 Dec 2023
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United Kingdom
I'm renovating my upstairs bathroom and have taken the walls back the the brick, and replaced the ceiling with PIR + new plasterboard.

I will be replacing the existing floorboards with 18mm plywood but I'm unsure whether I should:

1. Plasterboard the walls, then underfloor plumbing, then lay the plywood up to the plasterboard
2. Underfloor plumbing, plywood down, plasterboard walls on top.

or something else?

I'm nervous of 2, in case I need any adjustments to the plumbing. I wouldn't be able to lift the floor.

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I would do 2. But when you lay the flooring, cut the plywood to leave the pipework exposed.
You can then cut separate boards to do the infill over the pipes, which will be clearly visible if you need to remove them.
What will you e using for your final floor finish? Sheet vinyl, tiles, carpet? You can always write on the plywood 'Pipework' with direction arrows showing which way they run.
I would also advise keeping the plasterboard about 1/2" clear of the finished level in case the floors do get wet. This will prevent moisture being drawn up into the boards.
Thanks for the tips, the more I research 2 seems generally what people do. Depending on how the plumbing goes I'll have a go at your idea of cutting separate boards for the pipework.

It'll probably be a vinyl floor. Fingers crossed there'll be no floors up once I'm at that stage!

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