[endover750]

The venting pipe for my kitchen sink runs horizontally for a run of about 5 feet before it turns and runs up the wall and out. My problem is that the pipe runs about 4 inches above the level of my counter top. I have a new window to install there and the rough opening framing will end right in the pipe run. Can I drop this vent run down,( about 4-5 inches) for about two feet and then use a 90 degree to return it to its original run, connecting up again with the pipe going up the wall.

[argaiu1017]

Why don't u re-route your drain if u are on a subfloor and run up vertically along the king stud and dirty arm over to kitchen sink with your trap arm.
U may if your code allows u to do so. If so use medium sweep 90 for vertical to horizontal with vent, then use a long turn 90 to go up the wall. If this is exterior wall, run horizontal vent exposed under sink and run it back into wall and up.

[puffmugs]

States have different codes, but most codes require a vent to run vertical to 6" above flood level rim of fixture it is venting then may run horizontal until it turns to the vertical again.

[argaiu1017]

Yes, with structural issues where he has to install a window right where existing vent is, upc and cpc allows vents to run horizontal and slope it @ 1/4" per foot, or like I said run the vent along the king stud vertically and dirty arm with trap arm to the existing sink which is more work.