Shower and basin drain connections

[seanblee]

I've (mostly) gutted our ensuite and am now trying to decide the best way to provide a drain connection to the new shower tray and basin. The existing connections are as below. The main bathroom is through the wall on the right and there's a mini stack that the shower drain is connected to (along with the bath, toilet and basin in the main bathroom), with a 110mm running horizontally under the floor at the back to join the main stack on the left. Main joists run top to bottom, except there's a double trimmer running left to right next to the 110mm at the back that's carrying the joists for this section.

 

 

The existing basin connection is 32mm all the way with minimal fall into a vertical drop, and the drain used to glug whenever any water was run down it. I was hoping to find some 40mm somewhere but no joy, so I'm thinking about capping the 32mm and opening up the boss next to the toilet waste connection and running 40mm, reducing to 32mm where it comes out of the wall to the basin trap. Does that sound like the best option?

 

 

For the shower, the current connection from the mini stack is above floor level: 

 

 

The old shower tray was on some bits of 4x2 on edge and had a big upstand, so a huge step up and over. I'd like the new tray closer to the floor, so I'm thinking about capping the existing and cutting a channel in the chipboard floor, putting a strap boss on the top of the horizontal run at the back and dropping the shower connection straight into the top of it, something like this: 

 

 

I'd then raise the tray on a couple of layers of 18mm ply, so there's still a slight step but not as much as before. Is that the best option, or is there another way?

 

Many thanks in advance!

[Russell griffiths]

I personally would start from scratch and get it how you want it. 
pull the floor up, cut the stack off remove all those old bosses and fit a new section of stack with th bosses in the location you want them, get the pipes under the floor, get the tray down flush and have it right. 
anything else is just compromise. 

[Temp]

Ideally get all the pipes in the floor but that sounds difficult in this case.

 

It looks like you could run the basin waste in the floor if the trimmer doesn't go too far to the left?

 

As fir the shower..  Are the joists deep enough to put a hole through them? Otherwise is it possible to drop down from the trap through the floor and connect into the stack on the left below the joists. I guess that would mean boxing in the room below.

[seanblee]

There's going to be boxing along the left side of the room for a wall hung toilet frame so I'll be running the basin waste through that, it's really just whether it's worth up sizing to 40mm or if I should just reuse the existing 32mm - my gut says 40mm is a better job...

 

I'd love to have the shower tray flush but the joist layout makes it impossible - I really don't want boxing below and I'm not comfortable putting a 40mm hole through the double trimmer, feels like that's removing too much material.

[Russell griffiths]

If the hole is in the correct location on the trimmer then it’s not a problem, you can get reinforcement plates that fix to the side if your worried, or you can make up a reinforcement plate out of 18mm ply, glued and screwed on. 
you just need to avoid the standard plumber hack of cutting 50mm notches out of every joist 🤦🏻‍♂️
 

fit an air admittance trap under the basin. 

Edited March 15 by Russell griffiths