Hi there. I'm looking to put a washer and dryer on my main floor, where there was none before. We want to put a renter in there to be able to have a suite in the basement and a suite upstairs, so we want to try and keep as many walls upstairs closed as possible.

Anyway, here was my thought on it. I don't know if I could go to a 1 1/2" stack (I believe it will be around 12' to the main stack), but am I correct in thinking that I would need that re-vent in there? Also, are there any specific heights I have to worry about for stuff? Any suggestions are appreciated!Plumbing.bmp

Sorry about that, my picture didn't make it up there... no idea what in the heck that was about! Well, hopefully it'll work this time!

We want to put a renter in there to be able to have a suite in the basement and a suite upstairs, By the word "suite" are you referring to a bathroom group or simply a washer station? Your diagram is correct with one exception. If the stack you're venting into has ANYTHING else discharging into it from above you can't use it as a vent. You must either run a dedicated vent out the roof or run the washer vent up to a point where it becomes dry and revent back into it.
You will make the washer standpipe at least 36" long and keep the trap low to the floor. Use 2" PCVC for both washers.
You will have to open up the basement floor and locate the main for the drainage. You could also cut a sanitary tee into a existing stack but that's another operation in itself. Let me know what you want to do. Good luck, Tom

Depending on the code where you are at, or if you have to get a plumbing inspection, you can use Tom's drawing except instead of taking the vent through roof or back venting it, you can terminate the vent higher than the stand pipe with an air admittance valve, This is legal in many states. If there is no inspection this would be a solution for your venting. Also in my area any horizontal run to a washing machine must be 3" and change to 2" when you turn to the vertical with a 2" trap, On your picture it looks like you are venting the laundry box twice. Don't know your location or if you have to get an inspection, so that's the best answer I can give you. If access to venting is no problem Tom's installation would be the way to go.

As correctly stated by puffmugs, the 2" stack you identify in your drawing is actually vent. Question: is there 2nd story above with drains connected into the 4" stack ? Back to you. Milo

Question: is there 2nd story above with drains connected into the 4" stack ? Make book on it Milo! When's the last time you saw a 4" dry vent in a basement? Ya can bet yo "bippy" there's at least a bathroom group discharging into that 4" stack. Cheers, Tom

Sorry guys, I guess that should have been obvious information to include! This is for a washer on the main floor, and there is NO second floor. The ONLY plumbing that currently exists (from what I've drawn in) is the 4" stack. Everything else will be new.

If I run the 2" discharge pipe into the stack, the main floor bath will still be discharging into the 4" main. I thought be re-venting the laundry stack, I'd be able to drain into the 4" main and still draw air from the main through the attic, above all other fixtures.

Cutting a sanitary tee shouldn't be an issue, I wouldn't think? Don't I just cut a section of pipe out, put in a sanitary tee with a length of PVC on each side, and a banded coupling where the existing stack meets the PVC sections?

I guess I could get rid of that second stack... that wouldn't serve a purpose, I guess, right? I could just do it this way?

NO! You may not vent back to the 4" stack. As explained in other posts:
1. Run a dedicated vent up and either run it about the roof or revent back to a existing vent.
2. If local codes allow vent with a AAV,( air admittance vent)
Those are your only options. Good luck, Tom

Sorry Tom, I don't understand! Do you mean I can't discharge into the original vent, or do you actually mean I can't vent back to it?


If the stack you're venting into has ANYTHING else discharging into it from above you can't use it as a vent. You must either run a dedicated vent out the roof or run the washer vent up to a point where it becomes dry and revent back into it.

That doesn't mean that I can discharge into the 4" stack, and then run my new stack back to the 4" stack, in the attic? Sorry for being kind of stubborn, but if there's a way that I could make this work without having another hole in my roof, I'd like to do it! I just want to make sure that you're clear on my situation!

Thanks a bunch for all your help thus far guys, I appreciate it!

Yes! You may discharge your washer into the 4" stack but you can't revent back to it as explained above you have two ioptuions.
1. Run a dedicated vent up and either run it bout the roof or revent back to a existing vent in the attic.
2. If local codes allow vent with a AAV,( air admittance vent)
That 4" stack is picking up drainage from above and you can not vent back to a stack that has anything discharging back into it.
Sorry! V My fault. I should have explained it better. Tom

Oh, haha! Nope, sorry Tom! It's probably my fault for not explaining properly! This laundry room will be going on the top floor of the house, and I want to revent to the 4" stack in the attic! Basically, I'd be connecting back into the 4" stack two and a half feet or so below the point where it exits the roof.

Does that make it possible now? And if so, should I be using a 2" stack, or 1 1/2" would be fine?

My bad! I somehow thought this was a basement installation. However, I hope this job won't be inspected). By discharging into that 4" line you're creating a problem for the fixtures that are already using that 4" for a vent.
Do I think it will work? Yes I do. Will it be in code? No it won't.
Has a permit been pulled and will this job be inspected? Back to you, Tom

You can back vent into 4" stack in attic with 1 1/2" as long as it is above the highest discharging fixtures into 4" stack and developed length of vent is less than 50' which should not be a problem. As stated before they also make a Air Addmittance Box that is much like a Washing Machine Box except it can go in laundry room wall that has a grill on it for access to the air admittance vent.

Sorry for the 2nd post but Tom is correct this waste tie in for the laundry room should be below any vents that are already vented into 4" stack. As he said will it work? Yes most likely, is it legal? No

Nope, no permit has been pulled on it, nor will one be. We have a 20+ year old law here that allows homeowners to go permit-less, as long as the homeowner is the one doing the work. The theory is that the homeowner won't to try to screw themselves over!

Anyway, do you guys predict big problems for the downstairs (especially the tub and toilet)? I don't want to do a junk job that I'll hate myself for every time I think about it... but at the same time, it's simply not feasible to rip out a set of stairs and break up the concrete to be able to tie into the stack after everything else!

I CAN tie the new stack into the old just above the basement floor, but the only thing that would accomplish would be to discharge the washer after the downstairs bathroom sink... probably not a terribly amazing problem solver!

If it were me, and the job won't be inspected, I would do the job as pictured. If there's a problem you can always run a vent up in the attic and revent back to a existing roof vent. That would make your job legal. Good luck, Tom

Awesome! All right, thanks a bunch guys! I truly do appreciate you sharing your wisdom and expertise! I'm in construction myself, but I guess I've had my head buried in the carpentry and electric world for too long, without a visit to the plumbing section!

Stay happy and healthy... And even if it's not YOUR Thanksgiving this weekend, you might a well have a beer anyway! Cheers!