Advice on Adding Sink Drain to Garage Loft


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Old 12-03-22, 07:06 AM
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Advice on Adding Sink Drain to Garage Loft

Unfortunately this is an after thought.
New unfinished garage loft has no rough in plumbing for a small kitchenette sink.
The walls in the loft are 2x4 and the only path is dropping down into the garage level and running along the face of the studs and connecting into garage level bathroom. 10 foot ceiling in garage and I could box that in if I ever drywall (no plans for that), If this will work I am hoping to use 1 1/4" pipe to minimize footprint if it would be allowed.
Would the attached layout be code compliant?







 
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Old 12-04-22, 09:58 AM
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You know John, I think you are right, I was thinking about that 2" fixture drain below the joists like it was a trap arm. Let's see what Zorfdt says.
 
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Old 12-03-22, 10:08 PM
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Here is a little more explanation now that I'm home. Keep in mind I'm not the pro in this forum, and am only commenting until he comes along.

According to UPC table 7-3, a kitchen sink = 2 DFU, and requires a 1 1/2" trap. So no, you cannot use 1 1/4" pipe.

Secondly, you would likely want to transition to 2" pipe at or before the san tee (after your trap and minimum trap arm length) assuming it is going to be =/> 2 feet to get below your floor joists.

Table 7-5 indicates that the maximum a 2" pipe may run unvented horizontally (based on 1/4" of drop per foot) is 8 feet. So at 8 feet from the sink, you would need to tie that 2" pipe vertically up into your vent again, before continuing another 8 feet, where it would be tied into the vent again, and so on... until it reaches the stack. For these vertical tie ins from your horizontal drain to your vent you use a wye and 45 elbow or a sanitary combo wye... and it would be positioned on the 2" drain pipe at no less than a 45 degree angle.

So let's say it's 20 feet to your stack... with 2" SCH 40, you will have to tie into the vent twice along the way... and 20 feet at minimum 1/4" per foot will be minimum 5" of drop. With the thickness of the pipe and the corners you have to turn you would be tying into the stack a good 8 or 9" below the bottom of your joists. And it might be advisable to have a cleanout where you first drop below the floor joists, farthest from the stack...stuck in the end of a sanitary combo wye.
 
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Old 12-04-22, 08:30 AM
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So at 8 feet from the sink, you would need to tie that 2" pipe vertically up into your vent again, before continuing another 8 feet, where it would be tied into the vent again, and so on... until it reaches the stack.
Could that all be avoided by running a separate (2 inch) vent stack up through the roof at the sink location? Would a 2 inch vent have to be expanded to 3 or more at eh roof?
 
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Old 12-04-22, 09:00 AM
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The fixture vent, as he depicted at the san tee behind the trap is a given. And I would expect his existing vent is adequate.
 
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Old 12-04-22, 02:54 PM
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I'm not aware of the multiple-vent requirement. Traditionally, 1.5" piping for the drain and vent are acceptable. So the first drawing should (almost) work.
A few notes though:
1) The vent when it leaves the sanitary tee should go up as high as it can before turning horizontal. You need to go at least 6" above the flood rim of the sink, but with the window there, there's an exception to allow you to go as high as possible before turning horizontal.
2) I definitely agree with X about adding a cleanout wye in the garage.
3) As for 1.5" vs 2" for the sink drain... more and more plumbers are recommending 2" for kitchen drains as they tend to get gunked up with grease over time. As far as I'm aware, it's not a current code requirement (IPC or UPC) for 2" pipe, but it's recommended for longer runs.

So, long story short, your plan is quite reasonable.
 
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Old 12-10-22, 07:51 AM
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An atmospheric vent (one that goes up to the roof) is always preferred over an AAV (SureVent). AAVs have mechanical parts that can wear out over time and cause problems. You'd also need to confirm your area allows them - a lot of places don't.

But outside of that, yes, this is an acceptable use for an AAV. IMO, I would vent to the roof since you have an attic above and you're doing a significant reno anyway.

Lastly, I like your solution about placing the main drain by the oven and coming across to the sink. You can use something like this to re-support the window studs.
https://www.homedepot.com/p/Simpson-...-SS3/100375145

I would personally use 2" pipe on the vertical (and basement) drain, then use 1.5" for the horizontal arm to the sink and 1.5" on the vent up the wall and across the attic.
 
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Old 12-03-22, 07:25 AM
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hoping to use 1 1/4" pipe
​​​​​​​Absolutely not.
 
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Old 12-03-22, 07:34 AM
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Absolutely not.
This is helpful. Thanks
 
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Old 12-04-22, 11:30 AM
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Thanks for all of the details. I'd prefer not to implement another roof penetration.
Would the attached depiction cover what you guys are referring to?
Does the vent line to the stack need to have rise?
If it is and not to much trouble can you tell me the fittings I'd need at A thru F?
What size hole saw would you use for 2" pipe and is there any issue cutting that into 2x4?


 
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Old 12-05-22, 07:44 AM
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Thanks for the response Zorfdt. I will put a clean out in the drain. One vent line would be preferred.
Also - would this Oatey SureVent work in this application?
 
 

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