Bath drainage - passing through flooboards?

[marshr02]

Folks - could someone check my proposed layout. In particular I'm scratching my head regarding the bath drain. It's got to pass through the floorboards at some point (see attached jpg) - do I put the change of direction near the trap (as shown) or near the soil pipe using a 50mm vertical short pipe to connect into. Looking to avoid self-siphonage. I suspect there may not be a problem - but how would a pro do this?

Hopefully the jpeg is clear - the soil pipe is internal.

Cheers

 

[Henno82]

to be honest Marsh it looks pretty good as you have it, i can't see anything wrong with it

 

[marshr02]

Thanks for reply. Good to know.

Just curious though. I understood that when a drain pipe is diverted vertically downwards then you're supposed to go up one size.

e.g. When you join a bath waste to the main stack you're supposed to avoid the 200mm no connection zone if opposed connection - and the solution is a short vertical 50mm pipe that the 40mm feeds into.

So the bit that I'm just curious about is if - my vertical section wasn't at the trap end, but at the stack end then this should be in 50mm pipe. So what's different at the bath end? Is it because the section of pipe liable to run full bore is the section furthest away from the discharge appliance?

Cheers

 

[justlead1]

Hi. The fact that you have recognised the situation does not conform says something about your knowledge. With positions of fitment being dictated by clients and the facts they will not give up space to accommodate soil and waste pipes so they can be installed to comply with single stack codes of practice. One is often faced with problems. Putting my head above the parapet. I have often in similar situations increased the waste size (50 mm ) the 200 mm rule looks to be ok from sketch so the parallel junction you mention is not required, installed a 32 mm vent close to trap and using existing ducts/ voids / walls run back into soil / vent above highest waste. (in some cases up into loft via stud walls) This practice will avoid the self and induced syphoning to traps even when commoned. However it a different story where the soil/vent are serving flats/bathrooms on the floors above. Good Luck

 

[marshr02]

Thanks for reply justlead.

The 200mm and 'parallel' junction is not needed in my example as you saw. I just used it as an example to demonstrate that I believed a drain changing direction into a vertical section needs to be upsized at that point.

IF I fixed the bath higher then the entire drain run could be above the floorboards AND STILL JUST connect just on the bottom of the 200mm no connect zone. But this would make the bath difficult to get into

I'm interested in your suggestion for a vent pipe pipe, which I have the ducts for. The stack does serve one bathroom above. Your answer suggests the vent pipe always has to join the DRY part of the stack? So in theory I guess the 32mm vent could travel up alongside the stack and connect to the eventual dry section. I might keep this option in my back pocket as a retro fit if I have problems.

I think what I might go for is 50mm pipe from stack which turn 90 degrees up through floor. 40mm waste from bath would feed into this via a swept tee. The 50mm vertical upstand would be about half way between stack and bath.

I'm sure it's overkill, but I'd rather do it just a bit too well, than a bit too poor

 

[justlead1]

Hi. I am a bit out of touch with the paraphernalia that are available in the way of traps. But there was a time when you could buy traps with extended neck. So in the sketch you posted the trap would be below boards with the neck up through and connecting to bath waste. The venting is a take on the old one pipe system that utilised venting of all traps on systems. It stops all the gurgling that many new bathroom must suffer from. "this option in my back pocket" is about right and is handy when faced with an ifee situation. good Luck

 

[Keith Gillyon]

i presume that the pipe going under the floor is running with the joists because there is no way that the joists should be cut to accommodate a waste pipe, the easiest way is to fit anti-syphon traps on the bath & basin then u won't have to put in any extra pipework or worry about the water in the traps being "pulled" out

 

[marshr02]

Again, thanks for the replies. Interesting the 'extended neck' trap as that does the trick - only slight problem would be the trap would need an access hatch for any future maintenance.?

Keith - yes the drain is running with the joists IF the joists were running across the waste then presumably the waste pipe would need to fit above the floorboards (unless the bathroom was redesigned), and over a 2m run at 40mm/m the bath would sit too high.

I'm not keen on siphonic traps other than to retro fit a poorly designed installation - just a personal feeling...

cheers