wwhitney
In the Trades
3/4" plywood plus 3/4" foam is bit redundant. Some curbs are made of foam only, and then the foam needs to be thick enough to be structural. But if you have a 3/4" plywood frame for the curb, you could use 1/4" foam tile board. And at the widest part of the wye, you could certainly notch the 3/4" plywood frame, as long as the wye would not interfere with the 1/4" foam. As to the long turn 90, you could use a street connection there, either a street wye or a street long turn 90.
I guess in your situation, I might be inclined to leave the san-tee but turn the cleanout 90 degrees. That would ensure good access if the san-tee ever causes any trouble. Rotating the cleanout is quite a bit less rework than changing the san-tee to a wye.
[If you never have a backup on that shower drain, the san-tee vs wye will never matter. The concern is that you have a backup that includes solids, some of the solids get lifted into the horizontal vent section, and they don't drain out properly when the clog is resolved, due to the lack of the sweep on the san-tee, and they end up blocking the vent. Snaking the horizontal vent would let you clear that.]
Cheers, Wayne
I guess in your situation, I might be inclined to leave the san-tee but turn the cleanout 90 degrees. That would ensure good access if the san-tee ever causes any trouble. Rotating the cleanout is quite a bit less rework than changing the san-tee to a wye.
[If you never have a backup on that shower drain, the san-tee vs wye will never matter. The concern is that you have a backup that includes solids, some of the solids get lifted into the horizontal vent section, and they don't drain out properly when the clog is resolved, due to the lack of the sweep on the san-tee, and they end up blocking the vent. Snaking the horizontal vent would let you clear that.]
Cheers, Wayne