Re: cast iron stack - wet vent -- HELP please!
Posted by CEA on June 28, 2004 at 14:41:57:
In response to Re: cast iron stack - wet vent -- HELP please!
The common codes don't allow the drain from an upstairs bathroom to serve as a wet vent for downstairs fixtures. That doesn't mean it won't work or that it wasn't common practice 100 years ago, but it's a violation. All the downstairs fixtures (basement, kitchen and new bathroom) require separate venting. It's going to be between you and the inspector whether or not you have to bring the basement and kitchen into compliance when you add the new bathroom, but at least the new bathroom has to be up to code.

Having a P-trap doesn't eliminate the need for the vent--in fact, a main purpose of the vent is to prevent the water from being siphoned out of the trap. The drains from all the new bathroom fixtures can empty into the stack as long as each fixture is vented within an acceptable distance of its trap. UPC requires each vent to tie into its fixture drain within 45 degrees of vertical (no flat venting). Some codes are more lenient. The vents for the new bathroom can tie together no less than 6" higher than the downstairs sink, and then either run through the roof, or tie into the stack no less than 6" higher than the _upstairs_ sink. A 2" vent should be sufficient for the new bathroom.

I have heard that there are rare jurisdictions in which single-stack systems are allowed. A plumber or your local inspector can give you more locally useful advice. Good luck.

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