Kitchen Sink drain vent stack

jevard · Jan 27, 2008

I am installing a new kitchen and putting a sink in a counter that does not have a wall behind it. There is a waste vent stack in an adjacent wall, and my question is, what would be the best way/code compliant way to tie into it? See drawing for clarification. My house is one story with a crawl space below and no attic.

Jimbo · Jan 28, 2008

First, you cannot use that vent stack as the drain. You could come across from the sink with a 2" trap arm into a vertical san tee. The drain would come out the bottom of the tee down into the crawl space where you would tie it into a drain, and the vent would come off the top of that tee straigt up, or 45Âº, and connect to the vent stack. The new vent cannot be more than 45Âº from vertical, until it is 42" above the floor.

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SRdenny · Jan 28, 2008

Jimbo
Technically, the vent line can go horizontal below 42" if waste fittings are used. It just can't combine with another vent below 42".

jevard · Jan 28, 2008

Horizontal vent

Thanks for the responses... So is this correct: from the vertical sanitary tee the drain would go down and tie into a drain; the vent would go up turn 90 degrees to the right (so it is going horizontally around the back of the dishwasher) into the wall, turn 90 degrees, and horizontally tie into the existing vent stack? This is allowed if I use "waste fittings"? How are waste fittings different from normal fittings? Thanks again for your time.

SRdenny · Jan 28, 2008

In your situation, in which I'm assuming you're running your vent lines in plastic and not cast iron, the drainage fittings I'm referring to are long sweep 1/4 bends. Even using these, the 42" requirement for any tie in to another vent line is still in force.

jevard · Jan 28, 2008

Ok. So any time the vent makes a turn I would need to use 45 degree bends and eventually get up to 42" to tie into the existing vent? I will be using pvc, but the existing vent is cast iron. The existing vent was used for a half bath that was there, but is not being used by anything currently.

SRdenny · Jan 28, 2008

I said 1/4 bend (90), but a 45 (1/8 bend) is also allowed. Cut the existing vent above your point of connection and below it. Use a mission coupling (CP150) to connect to the sink vent and also to cap off the section of line coming up from below.

jevard · Jan 29, 2008

Thanks srdenny, I'll sketch up a quick drawing of what you've described to confirm. I am planning on using 2" drain and vent lines. I'm planning on providing a 3-1/2" chase behind the cabinets and dishwasher to allow for the vent line. I hope I can fit that 1/4 bend behind the dishwasher and into the wall. Thanks again for your advice.

Fidodie · Jan 29, 2008

jevard said:
Ok. So any time the vent makes a turn I would need to use 45 degree bends and eventually get up to 42" to tie into the existing vent? I will be using pvc, but the existing vent is cast iron. The existing vent was used for a half bath that was there, but is not being used by anything currently.

To the plumbers...

Is the vent still a vent if nothing is connected to it? sounds like it was a drain when the bath existed above it - if it isn't there anymore, then can it be a drain for the sink ???

on the flip side...it is may exceed an 8' trap arm, so you would be better
going down with the drain, and attaching a vent as suggested...

just tossing it out there...

SRdenny · Jan 29, 2008

I am planning on using 2" drain and vent lines.

You only need an 1-1/2" vent. If you're planning on tying into an existing 1-1/2" vent, you can't decrease the size of a vent midstream. So, if you run a 2" vent, it has to be at least 2" all the way through the roof.

jevard · Feb 15, 2008

srdenny said:
Jimbo
Technically, the vent line can go horizontal below 42" if waste fittings are used. It just can't combine with another vent below 42".

If the roof vent I am connecting to will only be used by this kitchen sink, can I tie into it lower than 42" (about 36")?

jevard · Feb 15, 2008

here's a pic of my question...

hj · Feb 15, 2008

drain

No picture. What is that "vent" line? Is it the old sink drain? If so, you can run it horizontally in the wall, then turn it out to the sink location. You would just have to make the vent connection close to that elbow and then return it back and connect it to the upper portion of the vent.

jevard · Feb 15, 2008

thanks hj... sorry I think I fixed the pic link now. I basically want to run a vent line horizontally at 36" until I hit the old vent stack. The stack will only go up from there to the roof. What do you think? Here's that pic again...

plan:

vent line to stack:

Kitchen Sink drain vent stack

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