Designing Kitchens and Bathrooms - question about venting a system

when venting ur plumbing system...does ur vent pipe ALWAYS have to travel in an upward direction...or can it possibly drop down 12 inches to clear an obstruction then continue up to the roof....any help...thank you...

Yes, and no. If ur vent is connected at the lowest point of ur drainage system then drops another 12 inchs chances are its not going to work. However, the vent can be placed any point beyond the fixture trap or before/at the lowest point in the drainage system. The vent pipe itself cannot be lower than the lowest point or it will not work. If u have a 12in vertical drop it will not work either. The vent ideally should be placed at the lowest drainage point in ur drainage system(Such as lowest point of drain pipes in Kitchen and Bathroom) If u are attempting to make a 12in vertical below the drain, the water will drain into ur vent system creating another water trap in which case ur fixture trap may fail and ur fixture drain will become a vent. I suggest pitching the drain pipe or angling at a 1/8in per inch till u can accomadate a 90' T or Elbow or even a 45'T or Elbow to establish ur vent

Goodluck, if u have more ??? post back