Washer Drain Pipe

[thedcdude]

I'm planning to change my washer drain from a laundry tub to a drain pipe. There is an existing 2" drain pipe from the floor. Do I need to vent the stand pipe? If so, can I use an AAV?

[HayZee518]

the sink has a trap in its effluent line. if you tap into the discharge of the sink you'll need to install a trap in THAT line. the stand pipe has to be about two feet long. I'd stay with the 2 inch diameter to make sure the washer's discharge will be big enough for all that water going through it. I'm sure lazypup will say something about this.

[thedcdude]

I'm planning to put a trap in the stand pipe, I was wondering if it needs it's own vent, or if whatever vents the sink will take care of it too.

[HayZee518]

The AAV is just to prevent back siphoning as in a dishwasher drain line - breaks the vacuum. I don't think you can use it as a breather for a seperate drain line - but there is a formula for figuring out how far from the main stack you can run a drain without venting. lazypup has that information.

[LazyPup]

In order to give a definitive answer I would need to know if your local code is modeled after the International Residential Code (IRC) or the Uniform Plumbing Code (UPC) because they each take some rather differing views on both the laundry standpipe and the required venting.

VENTS:
As an example, under the IRC all structures Must Have one “Main Vent” which must run undiminished in size from the house “Main Drain” through the roof. Once that is achieved we may decrease the diameter of any required auxiliary vents to ½ the diameter of the line they serve but not less than 1-1/4”. (In regions subject to frost an auxiliary vent must be increased to 3” at least 1’ inside the attic before passing through the roof.)

Under the IRC, in addition to passing through the roof, Auxiliary vents may be terminated in the attic space (never a good idea), through the wall (subject to some rather strict limitations) or we may use an unlimited number of AAV’s.

Under the UPC the size of a vent line is determined by means of code tables that define the number of DFU’s (drainage fixture units) of the fixtures served by that vent, and all vents must run through the roof. The UPC will allow a maximum of one (1) AAV per structure, with the expressed approval of the local AHJ. (Normally they will only approve an AAV when installing a sink in a kitchen island, and even then, most inspectors prefer we install an island loop vent.)

You stated in your post that you have an existing 2” drain line from the floor.

If you were under the IRC we would first have to examine that 2” line carefully to determine if there is a trap under the floor. If there is a trap, all you would need to do is install a vertical riser at least 18” but not more than 42” above the water level in that trap to make your standpipe. (Installing another trap on the riser would be code prohibited here)

The UPC does not permit the trap to be under the floor.

If you are certain that there is no trap under the floor, I am attaching an illustration for the UPC laundry standpipe. If you are under the IRC you could use this same configuration but instead of running the vent line through the roof, you could extend it a minimum of 4” above the sanitary Tee, then install a female thread adapter and an AAV. Since the AAV would be readily accessible and it can be easily removed, it would also serve as a cleanout. (If you are under the UPC and have no other AAV’s in the structure you could rely on the code exception that allows one AAV and place it here.)

[thedcdude]

Thanks for the info. I believe Maryland follows the IRC. Since my first post, I've noticed the 2" drain goes up through the upstairs floor to the kitchen sink, and then continues to vent through the roof. When I cut the pipe, I'll check for a trap below the basement floor. If there isn't one, I'll configure the stand pipe like your drawing -- minus the vent. Thanks again.