I am working on a 1950 bungalow. It was built with two vented DWV stacks...main stack supports bathtub with shower, toilet, and lav. It's 3" CI and goes underfloor. On the way back to the sewer main, there is a 2" CI hub fitted with a 1 1/2" galv drain. Originally, the galv drain ran up to the first floor, teed off a sink drain, and continued straight up to the attic. It then turned 90 degrees with a horizontal offset of 4 feet in the attic to clear the second floor kneewall, turned 90 degrees to vertical, then enlarged to 3" CI to pass through the roof.
Fast forward through a chain of years and owners, and the rubber boot on the roof penetration is shot, dripping water onto the insulation and kitchen ceiling. A previous owner also cut the vent pipe and galvanized sink drain out in the kitchen wall, and used a flexible coupling to connect a horizontal run of PVC from the basement section of the drain, just below the first floor joists. The upper part of the vent is uncapped and disconnected and dripping water in the wall cavity, and there is no sink vent at all. And the location of the sink is now a considerable distance from the vent stack, about five stud bays over.
I don't want to drill through all those studs in an interior bearing wall to tie in the vent. The original vent had already notched the top plates considerably. I can't move the basement DWV location. But since the main stack is vented and the only two fixtures to be drained and vented by this pipe are the sink and dishwasher, is it permissible to use an AAV above the trap arm to provide venting? Will 1 1/2" PVC be sufficient for a single basin sink and a standard dishwasher? The 1 1/2" hub is a packed lead joint, and it would probably be a bit of effort to try to fit a 2" PVC pipe due to its location right next to the stair stringer and a wall. Which is better, a compression fitting or a no-hub coupler if I need to upsize?
Of course, the existing vent would be removed and the roof repaired. I could attempt to remove the old galv and CI vent and tie into the new drain location, but I really am not a fan of horizontal vents in unheated attic spaces.
Fast forward through a chain of years and owners, and the rubber boot on the roof penetration is shot, dripping water onto the insulation and kitchen ceiling. A previous owner also cut the vent pipe and galvanized sink drain out in the kitchen wall, and used a flexible coupling to connect a horizontal run of PVC from the basement section of the drain, just below the first floor joists. The upper part of the vent is uncapped and disconnected and dripping water in the wall cavity, and there is no sink vent at all. And the location of the sink is now a considerable distance from the vent stack, about five stud bays over.
I don't want to drill through all those studs in an interior bearing wall to tie in the vent. The original vent had already notched the top plates considerably. I can't move the basement DWV location. But since the main stack is vented and the only two fixtures to be drained and vented by this pipe are the sink and dishwasher, is it permissible to use an AAV above the trap arm to provide venting? Will 1 1/2" PVC be sufficient for a single basin sink and a standard dishwasher? The 1 1/2" hub is a packed lead joint, and it would probably be a bit of effort to try to fit a 2" PVC pipe due to its location right next to the stair stringer and a wall. Which is better, a compression fitting or a no-hub coupler if I need to upsize?
Of course, the existing vent would be removed and the roof repaired. I could attempt to remove the old galv and CI vent and tie into the new drain location, but I really am not a fan of horizontal vents in unheated attic spaces.
Last edited:
