Shower tray former underboarding

[shaneswallow]

Hi,

Looking for some advice please. I need to underboard between joists for an Impey aqua-dec linear 3, 1800x900 shower tray former.

I only have 50mm depth for runners and the plywood, so I’m thinking 38mm for the runners and 12mm for the plywood to sit on as the ceiling below has exposed joists. I was advised I could get away with 12mm BB or birch faced plywood as its strong vs the usual 18mm. Is this setup ok for the tray to sit on with the joists running perpendicular to the tray at ~450mm centres?

To make things more interesting, there are already 20mm thick battens nailed to the joists which the ceiling below are nailed into as in attached picture, so the runners need to go onto this existing batten then screw the runner, batten and joist. So 20mm + 25mm runners = 45mm - what would be a good length screw and should there be pilot holes before screwing? The joists are 45mm thick.

Thanks,
Shane

[arco_iris]

No knowledge myself so not qualified to answer other than as a sensible diyer with forty years experience. Did My Own Research.........

My question to you, OP, is, given the information provided, how do you intend to connect the waste outlet 817mm centre from the rhs of the former to the waste pipe pictured in the right hand bay which only gives 425mm (450mm centre quoted less half width of joist) available?

Next, surface of former to base of trap is shown in the manufacturer's drawing as 117mm, but you suggest you have 22mm floorboard + 50mm above the ceiling, so only 72mm. Is the waste trap to go through into the room below?
In your image it is shown as 22mm + 18mm + 96mm (= 136mm) and at the bottom of my image, 151mm.

impey-aqua-dec-linear-3-wet-room-former-ad3l1890-3.jpg (45.93 KiB) Viewed 874 times

The alternative is raise the former, defeating the object of using it (not cheap, it seems) and the question goes out the window anyway.

Other than that I'd say 32mm deep battens with 18mm plywood. 4mm or 5mm screws, plenty of them, pilot holes not needed, length (width of joist + 20mm batten + width of 32mm deep batten minus 5-10mm).

[shaneswallow]

The waste on the right is for a temporary shower tray. We are drilling straight through the wall in the third bay along, left to right.
Yes the waste is intended to go into the room below where it will be boxed.
I want to avoid raising the tray, hence trying to underboard.

Other than that I'd say 32mm deep battens with 18mm plywood. 4mm or 5mm screws, plenty of them, pilot holes not needed, length (width of joist + 20mm batten + width of 32mm deep batten minus 5-10mm).

Cheers