On 02/06/2019 21:41, ss wrote:
I havent ordered tray yet.
Ideally I want a 1200 x 800 tray.
Unfortunately the waste connection would be directly above a joist.
A longer 1300 tray all appear to have the waste in the middle of the
tray and would need to attempt access to connect from the adjoining room
so trying to avoid that. I am trying to achieve a sort of walk-in so a
shorter tray I am trying to avoid.

Any thoughts on how to solve this I am reasonable at DIY, plumber will
make connections though.
See image.

https://imgur.com/fOlOTuR



Is that sketch accurate? Not much overlap where the joists are joined.
or is there a support underneath?

A very large tray with the drain in the middle is not a great idea. They
can snap in the middle, because that is the thinnest point and that's
also the most stressed point.

Mira do a 1400 x 800 with the waste at one end. Too long for you?

I thought you were going to raise everything up a bit, so does it matter
where the joist is?