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Sink plumbing vent offset

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Directly behind the previously installed light fixture in my bathroom is the vent for the sink.  The existing light fixture was attached to an electrical box screwed directly to the vent pipe.  I only need to move the stack about 6 inches to the right, within the existing stud space, to accomodate a properly installed electrical box.  Can I reroute the vent with 2 90 degree or 45 degree elbows to make room for the box?  The vent runs vertically, after it was rerouted it would jog to the right and then back to the vertical vent.
asked in Plumbing by sjcote (120 points)
edited by darekrudy
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1 Answer

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Hi Sjcote,
Under the IRC (International Residential Code) & UPC (Universal Residential Code) you cannot have a horizontal plumbing vent section (in case you use 90° elbow) if it is less than 6 inches above the rim / top edge of the sink; 45° elbows are permitted. I’m assuming the light fixture is much higher than that so either one of those elbows (90° & 45°) can be used.
There’s another restriction for a horizontal vent (UPC) that depends on its length. If you use 90° elbows and the combined length of the horizontal sections of your offset is more than 3', the vent size would need to be increased another nominal size. This rule doesn’t apply to 45° elbows so you can safely re-route the vent using them above and below the sink’s rim.
answered by darekrudy (21,730 points)