Installing a Kitchen Sink Drain Line
Need to clarify my understanding on venting & drain lines.
I’m looking at plumbing plans for a small residential project. The idea is to install a kitchen sink in a countertop that intersects the main wall that has a vertical vent pipe in it. The sink will be 4′ away from the main wall. There is a wall behind the sink that runs the length of the countertop to the main wall.
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According to the ICC (Table 909.1) – the max distance to a vent from a fixture sloped at 1/4″ per foot is 6′ for a 1 1/2″ trap.
I am looking at two ways to drain and vent the sink.
1. Simply have the drain line connect to the stack in the wall; This would slope down a 1/4″ per foot.
2. Have the drain line go through the floor and connect to the main drain line, and add a dry vent pipe that will connect to the wall’s vent stack.
Are either good? Is one more preferable?
Why is that the dry vent needs to point up 1/4″ per foot?
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Replies
Alex,
The horizontal runs on vents stacks need to be sloped so that they don't fill with condensate or rain.
I'm not clear on your second option. The trap and vent have to connect before you attach the he main drain..
A third way to vent the sink would be to use an AAV.
Thanks, sorry if I wasn't clear. To simplify - I have a sink against a wall that's perpendicular to a wall that houses a vent. The easiest thing would be to connect the trap arm to the vent fitting. I'm going to be less than 6' from the trap weir to the vent fitting, so it seems like I'd be fine. This looks like the optimal way to plumb this sink. This started because I thought I had to do an Island Vent detail.
I think what you're proposing going through the floor is an S trap and those are no longer permitted.
The spot where the vent attaches to the drain cannot be lower than the trap. The drain has to run horizontally until it meets the vent. The 6' length limit come the pitch of the pipe of the pipe and the diameter of the pipe. If the pipe is pitched 1/4" per foot and has a diameter of 1-1/2" inches, in six feet it falls one pipe diameter. After falling one pipe diameter it is considered to be below the trap.
If you cannot run the drain horizontally to a vent within one pipe diameter of the trap, the most common fix is to use an air admittance valve (AAV) as your vent. Prior to the acceptance of AAV's the way to do it was called "island venting" because it was how you could put a sink in a kitchen island. Basically there's no rule that vents can only go up, they can go down too so long as they have the proper pitch in the horizontal sections. Google it for details.
Yeah, just looking to connect the trap arm to the vent fitting, seems like the optimal way. I'll be at around 4' away, so that seems very much ok for a 1 1/2 pipe. Thank you for feedback!