Advice on waste water routing

[pilgrim]

Hello, 

I am looking for some advice on the best way to route the waste water for my bathroom. I have attached my planned bathroom layout. 

This bathroom is on the first floor, with the kitchen below and a small utility room below the shower / toilet end. The short wall that the toilet is on is the external wall with the drains connection below it.

The floor joists run north/south across the room so I do not think I can drill through them all that close to the wall to allow me to run all the waste water under the floor, but I could be wrong. I am happy to have the toilet waste going straight through the wall.

I want to connect up the shower bath and sink to a common waste outlet through a separate hole but avoid any back pressure causing waste to flow up into the bath when others are in use (as happened in the last house I rented!)

I do not mind if I have to drop down through the ceiling of the utility room in the corner below the shower, I am also happy to build a stud wall off the bathroom if this makes it easier to route the waste water, nothing is ordered yet so all sizes can change, measurements are to the existing walls.

Thank you

[Olf]

For me it looks doable: 32mm from the sink (preferably running in the wall and behind the bath) connecting to 40mm from the bath as close to the shower as possible, then joining to 50mm from the shower and out through the wall. The last stretch if ran in utility just sound insulate and box (though dropped ceiling is of course a bit more handsome). You still need either venting to atmosphere or AAV to make sure toiled does not suck out other outlets. I can see nothing bad in running toilet straight outside, just be careful with making the section through the wall at the right height (flex can only take so much at limited distance, and for sure won't make solids go up)

[pilgrim]

Great thank you @Olf will the stepping up from 32 - 40 - 50 mm pipes help to stop any pressure buildups causing water movements in the other units when one is draining?

[Olf]

No, the diameters are just dictated by the flow from each of the utilities and coincidentally in this case match the level of challenge to run them through the structure.

But as belt and braces you could add AAV at the sink, that way the pipework can equalise pressure if necessary