I am working on installing a 2nd floor bathroom in my house. The bathroom will be next to the water heater (though I may replace the 50gal with a instant demand heater) so water in to the bathroom is no problem. My problem is a drain for the sink, shower and toilet. The bathroom will be about 6' away from the vent pipe from the downstairs bathroom. Can I tie all three drains in to the vent pipe? If I tie it in at the top of the stud, it should have about a 3'-4' rise to the top of the vent.

Also, I was thinking I would raise the floor of the bathroom about 4" (using 2"x4" studs) so I don't have to cut in to the 2nd floor studs and would still have enough of a downward slope to drain the pipes. Will this work? Do I need to vent the new toilet with a separate vent?

Thanks

The bathroom will be about 6' away from the vent pipe from the downstairs bathroom. Can I tie all three drains in to the vent pipe?
If you do that you will have to disconnect the bottom bathroom vent from the stackyou're discharging the upstairs bathroom into anhd run a new vent out the roof or revent back to a dry vent at least 6 inches over the flood rim of the highest fixture. What you have done when you tied the upstairs bathroom to the vent was to turn it from a vent stack into a stack vent.

was thinking I would raise the floor of the bathroom about 4" (using 2"x4" studs) so I don't have to cut in to the 2nd floor studs and would still have enough of a downward slope to drain the pipes. You're figuring this pretty tight. A 2 X 4 true measure is 1 1/2 X 3 1/3. A 3" PVC pipe measures 3 1/4 OD. Not going to leave you too much room for slope. A typical bat roughs in like this.
Toilet connects to the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or revented back into a dry vent in the attic or if you're reventing back into a fixtures dry vent you must make your connection at least 6 inches over that fixtures flood rim.
With this configuration the toilet will be wet vented and will not require its own vent. Good luck, Tom

I'm not sure I understand. You are saying that if I use the current vent from the downstairs bathroom for a drain, I would have to run a new vent from the downstairs bathroom?? I don't understand the difference between a "vent stack" and a "stack vent". Is there another way to create a drain for the upstairs bathroom?

As far as raising the floor, I can probably raise the toilet and shower more (would 6" work) and leave the rest of the bathroom floor at normal level. I will check with local code enforcement as you suggest.

As you can tell, I really know nothing about plumbing. Electrical work is easy for me but plumbing just confuses the heck out of me for some reason.

Thanks