Fitting Low level shower tray on top of new flooring or before? Drainage and wastage systems and plumbing help, advice and answers

[Johndiy]

Hi, I'm having a new shower fitted including a low level shower tray. My builder has removed the old floodboards and replaced them with chipboard there is plenty room below for the waste. On top of the chipboard we are having new engineered oak boards fitted. My question is should the shower tray be fitted directly onto the new oak boards or should the tray be fitted first and the boards cut to fit round the tray, or does it matter? Thanks for your help.

[plumbbob]

The tray should not sit directly on the chipboard floor, but should be supported over it's entire area by at least 18mm of marine grade plywood.
So, this means, chipboard floor, plywood, and finally, tray bedded in to a layer of cement.

What I would normally do is cut the ply slightly smaller than the tray which will allow the oak boards fit under the tray for an inch or so. This looks neat, and solves the expansion problem.