Best way to route waste pipes

[DIYWarrior]

I'm renovating an ensuite bathroom and would love some advice on how best to route the waste pipes. The existing set-up is in the photo attached, where the Green marker is the current shower waste, Red is obviously the WC waste and Blue is the existing basin waste. This room is a 2nd floor side extension to the original house (the original house stack is boxed-in and the main bathroom and kitchen drain into it). I'm guessing whoever did the original plumbing put 2 x 90° elbows on the shower waste to attempt to stop backflow given the WC waste drains from above it (We never really used this shower so can't confirm if there were issues or not with it).

I'd like to move the vanity unit/basin but it'll mean it's waste is below the existing WC pipe. It'll also mean drilling through joists unless I route it along the brick wall the unit it attached to (that wall will be battened out).

What's the best options here in terms of waste routing for the shower and basin waste as my understanding is I want both entering the main stack above the WC waste?

Any advice appreciated!

 

[blup]

I believe there is a minimum gap between pipes going into the main soil pipe, otherwise seems fine

 

[Hugh Jaleak]

Crossflow prevention, regs don't allow any connection into the Stack 200mm below the centreline of the WC Branch.

Existing shower waste connection is absolutely fine, I suspect they used 2 bends to drop it slightly to allow adequate room to fit the Strap Boss below the socket on the Soil pipe.

Ideally I would not run the basin waste through the joists, if you can, go along the wall. Bear in mind Reg allow a maximum run in 32mm of 1.7m, advise to upsize to 40mm for anything longer.

Obviously the 'horizontal' sections need to be on a slight fall towards the stack, but I would also factor in room to drop the Shower waste down a few inches after it emerges through the wall to connect into the Basin run, belt and braces to ensure no problems down the line with water going back up to the shower if a full basin is discharged.

If using Solvent Weld waste fit Access Plugs as required to allow for future cleaning of internal runs.