Waste pipe sizes...

[matrixtiling]

I'm plumbing in a shower room on the 3rd floor of my sisters house (above downstairs bathroom). Fumbling about online (and the Screwfix catalogue) for info before I get going next week. Many thanks in advance.

Do I use 40mm pipe for a shower waste and t-into it a 32mm pipe for the basin?

Can I then connect this 40mm line into the 110mm toilet pipe just below the floor level?

Do I need a vent pipe (or AAV?) above the height of the sink u-bend?

 

[Richard C]

I'm plumbing in a shower room on the 3rd floor of my sisters house (above downstairs bathroom). Fumbling about online (and the Screwfix catalogue) for info before I get going next week. Many thanks in advance.

This work must (should!) comply with Building Regulations which also require forced ventilation (a fan) within the room; if a w/c is involved, there are other regs. to consider & if lighting is involved it gets even more complicated!

Do I use 40mm pipe for a shower waste and t-into it a 32mm pipe for the basin?

40mm minimum but if it’s a power shower, use 50mm. You can’t tee 40mm shower outlet into the 32mm basin waste; the flow rate isn’t enough & connecting 2 into one risks siphoning the traps unless you fit an anti-siphon trap or AAV. You should run separate wastes for each terminating directly into the stack but there are maximum length restrictions for unvented branch pipes.

Can I then connect this 40mm line into the 110mm toilet pipe just below the floor level?

You should connect each waste directly into the vertical soil stack if you can, teeing into a 110mm w/c branch will risk siphoning the traps when the loo is flushed

Do I need a vent pipe (or AAV?) above the height of the sink u-bend?

Probably if you run both outlets into a common waste.