The existing soil pipe that can be seen will be removed and replaced by one dropped into the floor void, out of sight
This is possible as the joists are running the right way
The shower valve and and the outlet for the shower head are plumbed into the back stud wall.
The shower trap wants to be right where a joist is.
To overcome this the top of the joist is notched out, allowing room for the trap, and the joist is strengthened by bolting another timber along one of its sides
The waste pipe from the trap has then got to pass through two more joists. To maintain strength, the hole for the waste pipe is drilled directly through the center of the joist, and as a precaution these joists are strenthened with extra timbers.
The result is a low level shower tray with a hidden waste pipe.
The back two vertical edges of the tray are completely covered with silicon before the tray is compressed against the waterproof Aquapanel. Excess silcon from the compression is then wiped 2" up the Aquapanel resulting in a totally waterproof joint with an upstand which the tiling will overlap.
The tray is then protected ready for the tiling.
A perfect neat black bead of silicon is applied between tray and tiling.