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Question on venting a loop vent against an exterior wall

Posted by sailr (My Page) on
Sat, Jul 21, 12 at 13:49


I know loop vents are typically for island sinks, but a large picture window is creating an obstruction to run a new vent for a sink we are relocating and I am hoping we can reuse the vent that is already in place with a few modifications.

As mentioned, the sink will be centered on a large picture window. This will put the old vent line upstream of the new sink. I intend to install a loop vent in the sink cab, but I can't run a new vent to the right of the window to tie it into. So, I am hoping the following will work out.

I want to detach the old vent from the waste line and run it horizontally past the new vent line just below the kitchen floor in the basement (sloped appropriately). This run would be about 6 feet horizontally and would be about 4 feet vertically above the waste line. The relocated vent line would be the last attachment to the waste line before it exits to the septic tank. In Massachusetts, the vent line the loop vent attachs to must continue down to the waste line and terminate there, which is a state modification to the UPC code. AAVs are prohibited.

So, if you were facing the kitchen sink cabinet, the loop vent would penetrate through the cabinet floor (drain and vent pipes). In the basement, you would see the vent line going to the roof on the left and it taking a sloped right turn above your head and in the direction of the waste flow. The two lines from the sink would come down and attach to the waste line, which is about chest height. The vent line from the sink would attach to the external vent pipe, which would be parallel to it. Everything is positioned correctly, but I just don't know if I am allowed to make that jog in the external vent line to get the pipe in the proper location. Hopefully the diagram makes it clearer.

Look forward to any input or suggestions.

Thanks in advance!

Follow-Up Postings:

RE: Question on venting a loop vent against an exterior wall

The line your showing as required by Mass is not correct

I have annoted a correct loop vent for Mass on the right side

RE: Question on venting a loop vent against an exterior wall


Thanks so much for your feedback. Your diagram makes my project a heck of a lot less complicated now, as my primary concern all along was that the vent pipe had to be forward of all the other plumbing in context to the direction of the waste flow and drain line (left to right in my diagram). Everything I saw elsewhere, including here, showed the waste running right to left and the vent as the last pipe in the line. Consequently, I thought I would have to install the reverse of what the pictures showed to accommodate for the different flow direction in my waste line.

Thanks again!

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