Basin and Bath waste pipe

[Joef]

The basin waste runs horizontally for about 2m in 32mm and the bath waste runs for about 1m before they meet and tee together. From the tee the waste pipe runs horizontally for about 2m in 40mm to the soil stack.
If you look at the pic the top pipe with the level on is 40mm bath waste and the lower pipe is the basin 32mm. As I said it runs for about another 2m in 40mm to the soil stack. There quite clearly is some horrendousness going on there which will be changed but where should the pipe size be increased and from what to what?
Can someone please explain how the pipes should run and connect and in what sizes to fit regs? Thanks

 

[Knappers]

Drainage and waste disposal: Approved Document H

Building regulation in England for foul water drainage and disposal.

www.gov.uk

Page 9 I think

 

[Joef]

Drainage and waste disposal: Approved Document H

Building regulation in England for foul water drainage and disposal.

www.gov.uk

Page 9 I think

Cheers for that. I see how the individual pipes should be but I'm still not sure how the principles apply when a tee is put in place. For instance if 32mm basin pipe was increased to 40mm after 1.7m, then ran for 0.3m in 40mm before the tee, do I then add on 1m of pipe in 40mm from the bath to the tee, so in theory there is now 1.3m of 40mm pipe at the tee? I'll have a proper look at this later but if someone can tell me if I'm thinking along the right line or way off the mark that would be helpful.

 

[Knappers]

Its probably ok in the sizes its in.
Could have 50mm up to branches if its easily done.
I think you must run in one type of pipe system (looks like pushfit & SW mix) or use appropriate adapters.
Obviously if it goes down hill then that's good too!

 

[Joef]

Its probably ok in the sizes its in.
Could have 50mm up to branches if its easily done.
I think you must run in one type of pipe system (looks like pushfit & SW mix) or use appropriate adapters.
Obviously if it goes down hill then that's good too!

When the basin runs the bath starts to gurgle I forgot to mention.
I did say in the first message that it was horrendous what there was.

 

[Knappers]

Anti-vac trap on basin would likely sort that

 

[Ric2013]

I think we need to remember that ADH is not the building regulation. It's a guide as to how one could meet the building regulation. In practice, an installation that works well but breaks the recommendations of ADH still works, doesn't it?

The way I was taught to understand your example:

For instance if 32mm basin pipe was increased to 40mm after 1.7m, then ran for 0.3m in 40mm before the tee, do I then add on 1m of pipe in 40mm from the bath to the tee, so in theory there is now 1.3m of 40mm pipe at the tee?

is that at the tee, you have 1m of 40mm pipe, this being the longest length upstream. This leaves you with a maximum of 2m to use downstream of the tee. That said, there's a flaw in this logic, as it does not entirely make sense to allow a maximum of 4m for 50mm pipe but allow a mix of 32, 40, and 50mm to a total of 7.7m, so it might make sense to take the 2m total length of your basin run, and say you have a maximum of 1m of 40mm after the tee.

The point is to avoid the pipes running full bore and sucking the water out of the trap or traps. Which is obviously a problem in your case.

It sounds like the issue is in the shared pipe after the tee as you say the bath gurgles (but not the basin): the suction is logically developing in the shared run therefore. I would suggest this would benefit from being increased to 2" (50mm). It may merely need resloping properly. It is surprising how many people don't bother to support waste pipes properly at frequent intervals.