I have rough in for a toilet and a sink. I would like to add a shower, how difficult is that?

Hi Bubbiej...

Are we talking about an UNDERGROUND ROUGH IN?

If so, and if WET VENTING is allowed in your area, then you could connect into the 2" sink drain line and run a 2"ptrap over to your shower... no additional venting required.

If wet venting isn't allowed then you would connect into the toilet drain line, behind the toilet vent, and run a separate 2" drain line with 2" ptrap and a separate 1.5" vent for the shower. The 1.5" vent would connect into the sink or toilet vent at a minimum of 42" off the finish floor.

You could also install a sanishower (Saniflo macerating and gray water pumping systems (http://www.saniflo.com)) that installs above the floor. This option requires special venting and in my opinion is just as much work or even more work than cutting into the drain pipes already present, but I wanted you to know about this option!

Glad to discuss more here. Let us know...

Mark

I have rough in for a toilet and a sink. I would like to add a shower, how difficult is that?
I'm going to assume the rough in is in your basement under the cement,
You will have to take up then cement and wye off the sink drain (see image) to pick up the shower, The shower will be wet vented and the bathroom group will be vented by the sink vent.
If wet vents aren't allowed in your area you will have to run a separate vent off then shower and revent back to the sink vent. Good luck on your project Tom

Purpose of under slab "rough in" is to accept above slab plumbing including connecting plumbing fixtures to it...