A friend of mine just tackled his own plumbing for a washing machine standpipe. He got some advice from me which was basically “don’t forget about the vent and you should get a plumber if you don’t know the venting requirements, which I don’t”
So he talked to a plumber who told him to “just go straight up”.
What he ended up doing was putting a wye in the standpipe and then continuing the standpipe (which is now a vent) up through the roof. The washing machine drain hose will hook into the wye.
This is 2″ PVC and it’s about 5′ from the main stack so I think he may be OK code-wise, but I’m wondering if there’s any downside to what he’s done with his “vent”. As I see it, it can’t hurt and it may even help water drain better, but I’ve never seen it done like this before.
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so the vent is downwind of the trap, eh?
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I can't tell from your description, but I think he did it wrong. There should be a tee with one end going down to the sewer connection and the other going up through the roof (or connecting to other vent pipes that eventually go up through the roof). Into the odd leg of the tee there should be a trap, with the standpipe feeding into the trap.
Does this guy's jury rig even have a trap?
OK, I'm a lousy artist, but here's a sketch. I hope this makes it clear. It's the 2" PVC that goes through the roof that I'm wondering about.
View Image
the riser is good...
move the trap between the riser and the WM inlet....
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Your friend is fine. Plenty of vent.
Only (non)issue is that the distance from the inlet to the trap does not meet current code. I was told this by an inspector on a project recently:
Inspector Jeff: 'Hey, skipj, this inlet can't be more than 42" above the trap.' (I think it was 42").
Me: 'Why not Jeff?'
Inspector Jeff: "New code says.'
Me: 'OK, but why on earth is that? How does this have anything to do with health and safety, efficiency, or anything? Really, just curious...'
Inspector Jeff: 'I've no idea. I'm not gonna fail you, just so you know, down the line, for whatever reason it's now THE CODE.'
So there it is for y'all.
I'd agree -- trap is too far from the vent stack.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
OK, why?
To avoid siphoning the trap -- the main purpose of venting.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Thanks for all of the information. Who would've thought there would be so many issues to consider for a "simple" standpipe... max 42" standpipe, distance from trap to vent stack, trap 6" above floor...
It sounds like, for all practical purposes, he'll be fine, but if the inspector gets out a measuring tape, he could fail on a technicality. I don't think that will happen. From what my friend tells me, the inspector is easy to work with and a lot of the plumbing is 20' high in his auto shop.
also doesnt the trap need to be less then 6" from the floor
The 4" stack is already venting the trap.The stand pipe must be min of 18" then put a 45 out the wall dont need the other vent as long as the trap arm is no more than 5' from the stack and the trap must be min of 6" above sub floor.Thats in Ca. May be different there.
That is unlike any system I have ever seen. Why isn't the vent down stream of the trap? The purpose of the vent is to protect the trap from syphoning, and in tthe case of this went vent system, syphoning is still possible. I have never seen a system that was vented upstream of the trap.
Agreed. I see no need for the vent on the standpipe. And certainly that vent must not be connected to other plumbing vents.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Agreed. I see no need for the vent on the standpipe. And certainly that vent must not be connected to other plumbing vents.
I think you may be able to tie into the 4" at some height, before the roof. The OP would have to do the calculations. An AAV could also be used
Edited 2/26/2009 10:40 am ET by McMark
I would think any tie in would risk venting sewer gas into the house.And no need for an AAV -- simply leaving the "vent" pipe open a few inches (or a foot or two) above the Y would suffice, if one sees a need for this scheme at all.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Regarding the venting issue:
Plumbing 101: Remember 2 things about traps: 1) traps are there to prevent entry of sewer gas; 2) vents protect the trap from either positive pressure (blowout of trap, or "burping" of sewer gas ) or negative pressure (sucking enough water from the trap to break its seal.)
Your sketch shows that the 4" stack has no other fixtures or drains dumping into it from above the washing machine branch: if this is correct, then there is no need for any additional venting. Since the washer would be the topmost fixture on the 4" stack, the 4" vent would protect the trap by relieving any pressure differences before they could affect the trap seal.
However, if there is any other drain above the washer branch, there is a slight risk that such drain could either suck out or blow out the trap seal on the washer trap arm. "Slight risk", because of the very large cross-sectional area of the 4" stack--it would take a huge slug of waste water to fill the 4" enough to restrict air movement within the stack sufficient to create enough pressure difference that would affect the washer trap. Even a toilet above (especially a low-flow toilet) would not, by itself, fill the 4" vertical stack enough to cause problems. In effect, the 4" stack is acting a a combination waste/vent system, that is, it is large enough to accept the drainage load, while still allowing for air movement within itself.
The vent arrangement shown in the sketch does absolutely nothing to protect the trap seal of washer since it is upstream of the trap--in order for vents to protect the trap, they need to be just before (downstream) the trap. That said, it is also true that the useless vent does no harm (except for creating an extra roof penetration and the potential for a roof leak.)
As a longtime plumbing inspector, my take on this would be to accept the original installation (even if there are other drains above the washer) by falling back on the code provision that acknowledges that some remodeling work can create situations where it is impractical to apply the letter of the code. Inspectors are supposed to understand the principles of plumbing enough to be able to make a judgment call when needed. (No, it doesn't exactly meet the code, but it will work, and no threat to health or property will be created.)
Another hole in the roof is my only concern
Here is what the code says:
"P2706.2 Standpipes.
Standpipes shall extend a minimum of 18 inches (457 mm) and a maximum of 42 inches (1067 mm) above the trap weir. Access shall be provided to all standpipe traps and drains for rodding.
P2706.2.1 Laundry tray connection. A laundry tray waste line is permitted to connect into a standpipe for the automatic clothes washer drain. The standpipes shall not be less than 30 inches (762 mm) as measured from the crown weir. The outlet of the laundry tray shall be a maximum horizontal distance of 30 inches (762 mm)from the standpipe trap."
Your friend may or may not be code compliant. When you say "standpipe 48" to trap", are you measuring to the bottom of the trap or to the trap weir? To be honest, I don't know what point on the wye the inspector would measure to determine the top of the 42".
* edit- The "code" is the 2006 IRC
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
Edited 2/25/2009 11:50 pm ET by JonBlakemore
When you say "standpipe 48" to trap", are you measuring to the bottom of the trap or to the trap weir?
I didn't actually measure it since the standpipe goes through the floor and there's another foot or so below the floor. Since the washer/dryer is above an auto shop, that means that the trap is about 20' high and not easy to get to. Even if it's 48", for another 6", I just can't see it being a problem (other than a code technicality). It's sort of like just having a deeper sink.
This means that the trap is NOT 6" above the floor as someone else mentioned it should be. I don't know how traps can always be above the floor. I see them in basements all the time. And for bathtubs, they have to be.
Don,
Listen to rdesign, and do what he says!!!!!!!!!!!!!!!!!!!
Thanks again to everyone for the information. And thanks rdesigns for "plumbing 101".
Based on what you folks said, I brought the venting issue to my friend's attention once again. We took another look at the standpipe and realized that it's a bit more than 5' from the main stack. He decided to re-do his "vent". He capped of the standpipe extension and added a genuine vent just after the trap. There's no question now about meeting the code requirement.
Since he's an auto mechanic and quite handy, it only took him about 2 hours to get it all plumbed correctly. All that's left is for me to repair all of the holes that he made.
All's well that ends well.