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Old 04-07-2010, 12:40 PM   #1
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Re-routing plumbing vent stack for sink around new larger window


I'm located in MN, and I currently have a kitchen sink under a 4' window and I want to replace this window with a much wider one. My venting / drain pipe is 2" ABS. From the P-trap the drain runs horizontally about 2' to a T. The top of the T vents straight out to the roof (about 6" from the edge of the window), and the bottom of course connects to the main drain line under the floor. I am going to be installing a window that is about 18" wider on the vent side. This means I need to re-route my vertical vent. My question is, can I make a C shape around the window using 45' elbows, or do I need to just turn it once go over a few feet and cut a new hole in my roof? Please see attached diagram of two separate options I am looking into.
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Old 04-07-2010, 04:43 PM   #2
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either option looks good to me. The double 45 would preclude the requirement for a new roof opening.


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Old 04-07-2010, 05:33 PM   #3
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With 2" ABS if you try to go sideways through the 2 by 4 stud ypu will weaken it excessively. I would reduce to 1.5" above the P trap and go 9-0 degrees, then up and back 90 to get to the original stack. Once above the top plate increase bask to 2: so you don't have to mess with the hole in the roof. You do not need a 2" vent (or drain) for a kitchen sink.

The reason for using 90's instead of 45's is to make it easier to drill the holes to insert the pipe. Try drilling an 1.5" hole at 45 degrees.
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Old 04-07-2010, 07:04 PM   #4
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Like rjniles said--If the sink is the only fixture being vented with that pipe 1 1/2 inch is a fine size.

while 45's are ideal--doing a horizontal under the window to a 90 should be acceptable--once you are in the attic you can use a bell reducer to return to the original size.

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Old 04-07-2010, 09:18 PM   #5
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LOL @ Mike

First : seconded on changing that vent to 1-1/2 " 2" is overkill and running it through a 2x4 wall would kill the wall.

I'm here. 90's are fine. You can go around the window and back to the original vent... more pipe and more fittings.

The only kicker when using 90's is you must be at least 6" above the flood rim of the sink before offsetting horizontally. If you cannot do this due to structural conditions of the window, then you need to go as high as possible, run the vent on grade (1/4" per foot) and use drainage fittings (minimum 1 long turn 90* where the vent turns from horizontal to vertical).

Hope that helps.
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drain , plumbing , route , stack , vent

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