Toilets, Sinks, Showers, Tubs and Disposals - vent or not to vent

Hello, i understand that every fixture needs to be vented. I am putting in a bathroom in the basement. i have the rough in (12 x 12 box) for the shower with 2" horizontal pvc coming in. This rough in is approximately 24' from the vent running up through the floor, which sits about 16" from the main waste and vent line. My question is this, do i have to run another vent pipe for the shower or is this pipe serving as a vent for the shower already. All of this rough in was done when house was built 3 years ago. Any help on this matter would be greatly appreciated, thanks

You still have to have a vent line off the shower drain. One reason being that if you don't, the trap of the drain will be sucked out and you'll have sewer gases coming back into the shower. Good luck and post back.

I know need a vent. is this already serving the purpose for the shower, or is it the main vent where i tie in the vent for the shower

Also was wondering if the vent should go before the drain in-line or can it go after the drain toward main waste, or does it matter?

Kevin, Have to admit I am a little lost here. If the rough-in was installed when the house was built, it is likely that the vent was also plumbed in. The vent has to go above the drainline (how far above depends on local codes). Example: The shower drain runs back into the wall and probably comes off a drainage tee which goes to the drain and the other part of the tee goes up the wall and then elbows back over to the ventstack or drainline to prevent sucking the water in the trap in the shower out. Hope this helps some.

Majakdragon, I looked at my original post and forgot to mention there was a whirlpool going in also. I can see how i confused you, and myself. Bottom line is the rough in for the shower (12 x 12) opening just needs a trap. The Whirlpool will have it's own vent line running from it's drain line to vent.
(I originally had drawn two vents attaching to drain line for whirlpool, hence the before or after the trap for shower....Sorry. Just want to say thanks for your reply and your time, take care