Vent requirement for laundry washer drain pipe - DIY Chatroom

WaldenL · 01-12-2009, 05:09 PM

We're moving our laundry to the second floor. I understand (I think) the requirements for a vent, specifically allowing air into the system to break the vacuum that could drain the p-trap.. However, in the case of a laundry pipe won't the air go in directly from the top of the pipe? I don't see how to vent this drain since it's an open piece of pipe.

-Walden

RippySkippy · 01-12-2009, 05:16 PM

You're mostly right. The problem happens IF, during the discharge, the flowing water could create a suction that pulls the water out of the trap. IF you have a vent in close proximity...it will pull the air from the vent rather than through the trap where there would be more (water) resistance. Make sense?

WaldenL · 01-12-2009, 05:19 PM

Ah, right. The vent is on the drain side of the p-trap so it's easier to pull air from the vent than through the p-trap. Hmmmm.... I don't have a vent anywhere near this installation, and I don't really feel like cutting through the roof. Might have to crawl around the attic this evening.

II Weeks · 01-12-2009, 05:24 PM

depending on the type of roofing and pitch but putting in a roof vent is not too hard if you cant find a near by existing vent to tap into. Just a reminder, even though its a vent, you still have to pitch that pipe.

RippySkippy · 01-12-2009, 05:27 PM

depending on where your at...it might be worth your time to check with your local code officials to see if you can tie into an existing vent...and if they have regulations when doing so. In some cases you may be able to use an air admittance valve....but again...check with your local officials.

zosoplumber · 01-12-2009, 07:15 PM

If the drain is going to be in a accessible area you could add a studer vent(mechanical vent) before the p-trap. Not the best solution but it would work.

WaldenL · 01-12-2009, 07:27 PM

"Before the p-trap"?? Before, as in, street side, right? The AAV would go on the waste side of the p-trap, no? The other side of the trap from the washing machine.

II Weeks · 01-12-2009, 08:26 PM

maybe this drawing will you. sub the sink for your washer. its a good idea if its allowed where you live. couldnt be easier

WaldenL · 01-12-2009, 08:31 PM

Right, makes sense, AAV on the downstream side of the trap. And I'd think it to be a good idea that it's above the flood level of rim, even if not required by code, seems to be asking for trouble otherwise.

Daltex · 01-12-2009, 09:11 PM

Above the flood level is a good idea. Also make sure it's not over a bedroom as the AAV is loud when the machine drains. It also has a limited life so out the roof is best but if not easy then use the AAV.