Laundry Sink Venting Options

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JByo

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I would like to add a sink to my laundry room. The laundry room has finished walls and currently contains a washing machine outlet box with the typical fittings. I cut back the drywall to expose the plumbing and this is what I found:

byo-current-plumbing.jpg


It all seems pretty standard with the exception of the standpipe reducing to 1.5" pipe halfway down. I will speak to that oddity (and code violation as I understand it) later.

The sink will be installed to the left of the washing machine. The drain and water supplies for the sink will be in the stud bay just to the left of the bay that contains the washing machine outlet box in the photo. I have designed two different plans for the piping but I am not sure if one of my options is valid because I am unclear on the codes related to vertical wet venting. My two pipe designs are:

byo-design-options.jpg


Ignoring any water supply differences, option #1 uses a dedicated vent for the sink drain and I know that configuration would pass inspection just about anywhere. Option #2 makes use of what I believe to be vertical wet venting and as a result is simpler (less material and labor) but I don't know if it is allowed. The fact that the washing machine drains above the sink has we wondering if it could possibly siphon water out of the sink trap. The trap arm for the sink will be approximately 54" long to the 90 degree elbow that will then lead another foot to the trap under the sink. I seem to remember something about a 60" max for the trap arm (in 1.5" pipe) so maybe option #1 is really my only option? If so, could I bump the trap arm to the sink to 2" pipe and then do option #2?

If it helps, my water company dictates code for me (https://www.wsscwater.com/files/liv...Info/2019_WSSC_Plumbing_and_Fuel_Gas_Code.pdf). They are using IPC 2018 with some small modifications but nothing related to venting specific to my situation afaict.

The water supply arrangements I drew are really reversed. If I use option #1 for venting I am concerned I won't have the room (see below) to route copper around the pipes. As a result, I would likely do PEX in that case. I haven't done PEX before so I would have to buy/rent the tooling but not a big deal.

As for the standpipe reduction... the pictured wall is an exterior basement wall. As a result, I can only assume that the use of rigid foam insulation in the middle stud bay was done to protect standing water in the trap from freezing. The foam insulation is 2.5" thick and I guess that didn't leave them enough room to run 2" pipe between the two stud bays.

The wall is a standard 2x4 framed wall with additional 2x4s nailed on their sides to the vertical members in order to build out the wall an additional 1.5". Behind the stud wall is a (full wall height) concrete foundation wall. My plan is to pull the foam insulation and replace it with something thinner (2" maybe?) so I can run 2" pipe for the washing machine all the way to the drain line. I assume 2" foam will be enough to avoid any freezing problems but I also have other plans for preventing freezing even if 2" isn't enough.

Hopefully that all makes sense. I really do appreciate any insights anyone can provide. Thank you.
 

Terry

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Option 1

The laundry sink is 2" until the vent. The vent and trap arm can be 1.5"
The trap arm either comes off a vertical 2 x 1.5" x 1.5 santee, or a 2 x 1.5 combo on the horizontal bushed down to 1.5" for the trap arm.

The washer gets 2" and can have a 1.5" vent.
 

JByo

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Terry, thank you for the response. I figured Option #1 was the way to go but was hopeful there was a way to make option #2 work. I guess not.

In regards to your suggestions, and just to be completely clear, I have revised my Option #1 drawing below. The changes are done in purple. Did I interpret what you said correctly?

byo-revised.jpg
 

JByo

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Thanks again Terry. At least I know I generally understand what is going on :)

My final question and then I will head out to buy supplies... what is your opinion of installing a clean out on the drain stack? There isn't one there now but would adding a sink make me want to install a clean out? Or maybe just a "while I am in there" type of thing? If so, my understanding is I would want to place it above the flood level of the highest point (the washing machine outlet box in my case) or are there other factors to consider? Would I choose A, B, or C in the below image?

byo-cleanout-options.jpg
 

JByo

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For anyone (probably no one ;)) who is curious how this turned out, here is a photo of the finished product:

washer-rough-byo-after.jpg


I did end up adding a clean out in position "A" because why not. I had to get creative with the standpipe (relative to my initial planning) in order to accommodate the water lines. The vent pipe for the sink really did get in my way (why I was hoping to avoid it) but it all fits in the wall so all good.

This was my first time working with PEX. I chose Uponor because it made the most sense to me out of all of the systems out there. And I have to say, after this experience I plan on avoiding copper in the future whenever I can. Uponor was so easy and so quick that I honestly don't know why anyone chooses to do copper anymore (let the flame wars begin;)).

I have more work to do with closing up the wall but I am going to let things sit in the open for a while while I make sure there are no leaks. In the meantime, my next project is replacing my PRV and adding a Phyn while I am "in there". Thanks for all the help and happy plumbing to all!
 
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