Greetings. We're renovating a 1940s house with a basement, and plumbing rework is necessary. The kitchen and bath share a 6" wet wall. The kitchen sink is moving 15 feet away from the 3" C.I. main stack, to a new location in a small dining room addition over a separate crawl space. The fixtures to be served are a single basin sink, a dishwasher, and a garbage disposal. The new drain pipe will be 2" diameter and will be vented under the sink cabinet with an AAV, and routed under the floor joists in the crawl space, through the basement wall, and to the main stack.
In addition, the location of the toilet and vanity in the bathroom are reversing; now the toilet is about 5' from the stack and will be much closer afterward. The vanity now drains into a galv pipe opposite where the kitchen drain was and has no separate vent, and will also be moved to below-floor, with AAV in the vanity since it backs up to a bank of cabinets and a tiled wall behind.
Two different plumbers have presented two different layouts, one of which places the closet bend takeoff above the kitchen and vanity drains to preserve basement headroom, the other in a 3-in x 3-in x 2-in x 2-in dia PVC Schedule 40 Hub Double Sanitary Tee Fitting. Both propose rebuilding the stack from below the new fittings all the way up to just below the roof penetration.
Assuming there will be no issue with making a hole in either the rim joist or CMU wall to run the new kitchen drain at the proper pitch, is there any technical reason to prefer either solution? Due to the location of the sink and the foundation of the addition, there will be a 45 degree change in horizontal direction required where the pipe enters the basement to reach the stack, and potentially a change in vertical direction in excess of the typical slope if the combo is not used.
In addition, the location of the toilet and vanity in the bathroom are reversing; now the toilet is about 5' from the stack and will be much closer afterward. The vanity now drains into a galv pipe opposite where the kitchen drain was and has no separate vent, and will also be moved to below-floor, with AAV in the vanity since it backs up to a bank of cabinets and a tiled wall behind.
Two different plumbers have presented two different layouts, one of which places the closet bend takeoff above the kitchen and vanity drains to preserve basement headroom, the other in a 3-in x 3-in x 2-in x 2-in dia PVC Schedule 40 Hub Double Sanitary Tee Fitting. Both propose rebuilding the stack from below the new fittings all the way up to just below the roof penetration.
Assuming there will be no issue with making a hole in either the rim joist or CMU wall to run the new kitchen drain at the proper pitch, is there any technical reason to prefer either solution? Due to the location of the sink and the foundation of the addition, there will be a 45 degree change in horizontal direction required where the pipe enters the basement to reach the stack, and potentially a change in vertical direction in excess of the typical slope if the combo is not used.
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