= ED

: : 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?

: Yes.

: : 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).

: If they are code in your area, then yes.

: : 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?

: Most codes would require at least a 2" pipe when the toilet is served.

: : If we had to add another vent, could we tie into the attic stack at the three inch point?

: Yes

: Most of it is in the attic is 3 inches running through the roof...1 1/2 vent going to 3 inches.