The schematic below should make it clear the configuration I would like to use. Basically, I would like to keep the vent under the floor for a little ways, so it pops up in a better location. I cannot easily move the 2" drain location going down and would rather not go straight up from the location because of flooring issues.

the specific questions are: while the vent pipe is under the floor, if i am sloping at least 1" for every 4' as code requires, is it OK that the vent pipe is lower than the drain height? And second, for this configuration, is it OK to use a vent elbow instead of a sanitary elbow? I heard that vent elbows might not be allowed even though it's for a vent in certain cases, so that is why I ask the second. Unfortunately, I need to use a vent elbow to obtain the sharper turn to keep the vent under the floor...

http://students.washington.edu/jetpeach/07/ventdiagram.jpg

Thanks!
Jet

Vent pipe connections to the drain line are below the height of the drain. I think you are fine. However, you have drawn a 90 degree "T" for the two drains and the vent. I'd use a street T for the two drains so you won't get any splash going up the vent.

"the specific questions are: while the vent pipe is under the floor, if i am sloping at least 1" for every 4' as code requires, is it OK that the vent pipe is lower than the drain height? And second, for this configuration, is it OK to use a vent elbow instead of a sanitary elbow? I heard that vent elbows might not be allowed even though it's for a vent in certain cases, so that is why I ask the second. Unfortunately, I need to use a vent elbow to obtain the sharper turn to keep the vent under the floor."


If the vent stack is dry I can find no fault with your layout. A vent ell's acceptable in place of a regular elbo.
Although you don't show it, the shower is trapped isn't it? Regards, Tom

Thanks!
Yes, the shower is trapped.
ballengerb1, thanks for the advice on the street T, I'll have to see if I can find one at the plumbing store...

the schematic below should make it clear the configuration i would like to use. basically, i would like to keep the vent under the floor for a little ways, so it pops up in a better location. i cannot easily move the 2" drain location going down and would rather not go straight up from the location because of flooring issues.

the specific questions are: while the vent pipe is under the floor, if i am sloping at least 1" for every 4' as code requires, is it ok that the vent pipe is lower than the drain height? and second, for this configuration, is it ok to use a vent elbow instead of a sanitary elbow? i heard that vent elbows might not be allowed even though it's for a vent in certain cases, so that is why i ask the second. unfortunately, i need to use a vent elbow to obtain the sharper turn to keep the vent under the floor...

http://students.washington.edu/jetpeach/07/ventdiagram.jpg

thanks!
jet
If you are trying to plumb this to code, the medium sweep street 90 is fine for going from horizontal to vertical, but being below the flood rim level of the fixture being vented, the 90 going from vertical to horizontal should be a long sweep 90.