First floor bathroom / bathroom en-suite wastes

[Rishard]

Hello, just scouring the web / forum for similar ideas relating to first floor waste runs. I’m trying to work out the best way to route my waste pipes back to my stack. 
 

Is it best to try group the en-suite shower/basin/w/c into one 110mm pipe and back to the stack, or keep w/c separate from the basin and shower? From my research, these could step up to 50mm pipe from the basin/shower and back to the stack. 
 

OR 

 

Should I be trying to group say the w/c from the en-suite and the bathroom on the same 110mm run to the stack? Keeping the en-suite basin / shower on one 50mm run and do the same for the bathroom? 
 

I have posijoists which I can route most of these runs in. The w/c near my stack could go through the wall if beneficial. 
 

I’d also take some advice on good way to fix all this pipework to the posi joists. I thought about using some rips of ply to use as a side wall which I could clip / fix pipes to (on a fall) but if there are any other good bracket fixings people have used which would take up less space I’d be interested to know. 
 

Has anyone used much dampening on the larger soil pipes to reduce noise? Just a thought as the stack is currently coming up in the corner of a bedroom. This could be adjusted to come up in the bathroom if it makes more sense. 
 

Thanks for any insights. 
 

Stack highlighted red
 

 

[Rishard]

Excuse the badly written title. Can’t seem to change it now it’s live. 

[MPx]

Will be interested to see the "right" answers to this, but my layman take is:

 

Have the soil stack in the bathroom rather than bedroom if poss - it will make a noise but can be lessened with boxing in and sound deadening insulation.  You only need one 110 pipe with a suitable fall running from the top right corner of the En-suite to the stack in the corner of the Bathroom.  The toilets will need their own branch in at 110, but all of the other elements can be run in their individual 40mm/32mm pipe to the nearest point on the 110 and connect in there with an adaptor  Of course they all will need their own individual trap near their outlets.  The stack needs to run up and out above roof level for venting - and if it was me I'd put an air admittance valve above the outlet of the basin in the en-suite (the furthest element from the stack) and that will stop any gurgling - but many don't seem to bother with AAVs and accept gurgling.

[Rishard]

I agree, main soil stack can be dog legged to come up in the bathroom which makes sense. Are you saying the 2 toilets should have their own 110mm run rather than joining together before joining the stack. 
 

Once the en-suite toilet waste is in the joists, is it ok to join on to this run with say the shower waste? Would I use a strap boss onto the 110 or is there a better method? 
 

 

[MPx]

No not separate runs, just one pipe right across the back wall into the stack.  Each toilet will need its own local branch.  The other wastes can all individually go into the nearest point on the main 110 pipe using adaptors. Don't really like the sound of a dogleg on the stack - didn't realise that was the implication of moving it into the bathroom.  I'd probably leave it straight ... but its no different really to your 110 pipe feeding across from the en-suite so would work.