Combining Bath and Basin waste pipes

[Rodolphe]

Hi WRAS Gurus

I have this bathroom project which requires me to relocate a basin and run a waste pipe through the joists across the whole bathroom to reach the stack.

However there is already a bathtub there, which I'll have to move, and I would like to use the existing 40mm bath pipe, connecting the basin to it instead of running a new, separate waste pipe.

Page 7 of the Doc H states that "Branch pipes should discharge into another branch pipe or a discharge stack" (1.7) so I believe I am allowed to make that connection.

Am I right?

 

[TBServices]

It's not recommended.

 

[Rodolphe]

Understood, but is it compliant? I'll only know how easily I can fit a separate 32mm waste after lifting the boards. If it turns out to be possible without wrecking the joists I'll do it, but I want to have a plan B

 

[PlumbBobBob]

do you want to connect to the 40mm from the bath, with the bath still connected or are you running new for the bath from a new location?

 

[Rodolphe]

The bath will turn 90 degrees but water in and out will stay in place, so I anticipate I'll be able to use existing waste for the bath. My hope is to plug onto that for the basin waste.

I don't yet know how the waste for the bath is running, whether it is through the joists or another way. It *could* be chased in the wall, perhaps.

If it's through the joists, my concern is making another set of rather large holes and potentially weakening the joists. I believe it might be preferable to plug into the existing waste pipe if that's the case.

 

[PlumbBobBob]

it should be fine if you fit a hep2o valve to prevent auto siphoning of the basin trap when you empty the bath

 

[TBServices]

it should be fine if you fit a hep2o valve to prevent auto siphoning of the basin trap when you empty the bath

Bit excessive. Anti vac trap will do same job.

 

[PlumbBobBob]

Bit excessive. Anti vac trap will do same job.

or that indeed

 

[TBServices]

or that indeed

Just read my post, didn't like how blunt it sounded lol. Only said that as hep valves are expensive.

 

[chris watkins]

Best off using an air admittance valve installed as high as possible under the basin IMHO much better than anti-vac traps which are prone to leaking / sticking.

Ventapipe 40/50 Air Admittance Valve | McAlpine Plumbing Products

If I was you it might also be worth while having a look at Part A before you go cutting into floor joist & walls !!!! to give you an idea joist can only be cut into by a max of 1/8 of their depth & then only in certain zones.

 

[TBServices]

View attachment 9410Best off using an air admittance valve installed as high as possible under the basin IMHO much better than anti-vac traps which are prone to leaking / sticking.

Very true, although they're convenient.

 

[Rodolphe]

Brilliant input guys. Thanks a lot!

 

[AWheating]

you will find you cant notch that deep on most standard joists as it makes them too weak, you will have to drill the joist centers between 25 and 45% of its span. (span of joist not room)

 

[Rodolphe]

you will find you cant notch that deep on most standard joists as it makes them too weak, you will have to drill the joist centers between 25 and 45% of its span. (span of joist not room)

Yes, I didn't think I'd get away with notches.

I haven't looked into it yet, but I assume I can find somewhere some flexible 32 and 40mm pipe to do that? Because the standard rigid pipe will never do if I have to pass it through drilled holes.

I really hope I can re-use the existing 40mm and pipe into that instead as suggested above. Would make my life so much easier. Quite happy none of you guys came up with a regulation preventing me from doing it 🙂

 

[Howsie]

This is where I depart slightly from the regs. I'd tee into the 40mm waste depending on where it pops out. You'll rarely get siphoning from he bath to basin as its usually to a hopper just outside of the bathroom.

 

[Rodolphe]

My understanding is that branch pipes should not discharge into open hoppers though.

Howsie, don't you sleep at night? 🙂

 

[chris watkins]

Yes, I didn't think I'd get away with notches.

I haven't looked into it yet, but I assume I can find somewhere some flexible 32 and 40mm pipe to do that? Because the standard rigid pipe will never do if I have to pass it through drilled holes.

I really hope I can re-use the existing 40mm and pipe into that instead as suggested above. Would make my life so much easier. Quite happy none of you guys came up with a regulation preventing me from doing it 🙂

DON'T you dare use flexible waste pipe, call yourself a Plumber !!!!!!!!! What ever next. You will be telling us you are going to be using plastic pressure pipe instead of copper next. LOL
(please don't use it there is only so low you can go)

 

[Rodolphe]

LOOOL. Message received. Don't worry I do have some pride, I was not going to stoop so low.