Length of branch pipe for bath

[frediaz]

Me confused. The Marley drainage above ground catalogue says that table
8 of BS EN 12056: 2000 says that there is no maximum length for 40 or
50 mm drain branches for a bath. Whereas Building reg H (and text
books) say that the maximum length of the pipe is 3 metres for a 40mm
pipe and 4 metres for a 50mm pipe. Which is right?

I would like to put the bath in a better position that would make me
have a pipe 3.7 metres long but I want to use a 40mm pipe to reduce the
size of the holes in the floor joists.

This is a single stack system with ventilation through the roof.

 

[chrishutt]

Just go ahead and do it in 40mm. Try to achieve a modest fall and minimise bends (avoid knuckle bends). In the unlikely event that there is self-syphonage (gurgling when the bath discharges) you could fit an anti-syphon trap.

 

[frediaz]

Thanks. And am I taking a risk by connection 2 baths to one 40mm pipe or should it be one pipe for each bath?