Smooky
In the Trades
Technically you are correct, a vent should not be installed within two pipe diameters of the trap weir but I doubt that is where the odor is coming from. Have you considered any other possible sources? Where does that dryer vent go? Does it vent out near a sewer vent? Often odor enters the living space where it is supposed to vent out. Also when the dryer is running, it is blowing a lot of air out and pulling air from wherever it can get it. When the sheetrock was put up a screw or whatever could have gone through a pipe. Are there other plumbing fixtures in that area that we don't see? You could stir up a lot of trouble but I don't think the juice is worth the squeeze. Even if you do lengthen the trap arm, I'm not convinced that will solve your odor problem.