Basement Plumbing
Posted by Ed on May 23, 2003 at 13:22:23:
We want to install a full bath in the basement as well as a kitchenette. (4 fixtures)

Can we branch off a 3" basement drain pipe that already
receives flow from main floor: Kitchen Sink, dishwasher, clothes washer, laundry tub, lavatory, shower and toilet?

Regarding venting: Could we use air admittance valves
(below grade) for any or ALL of these fixtures instead of conventional venting? (AAVs are code compliant in our area).

There is a vent pipe connected downstream from the main floor toilet it serves (as well as the other main floor fixtures listed above). Problem (?) it is only
1 1/2 diameter and shoots straight up from basement joists through first floor wall and then in attic bends 90 degrees twice before going through the roof.

This 1 1/2 vent serves a horizontal drain pipe in basement joists below floor again serving all those fixtures noted above.

If we went with conventional venting, would this 1 1/2 vent (one story home) to the roof be adequate to add the 4 new fixtures in the basement?

If we had to add another vent, could we tie into the attic stack at the three inch point? Most of it is in the attic is 3 inches running through the roof...1 1/2 vent going to 3 inches.

Any and all advice is appreciated.
going to the three inch roof vent

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