Mark.

I am not doing a damnd thing until I am sure what needs to be done.
On the 3" that I am running from the crawl to the attic, Can I tee off that and connect to the 4in steel stack that is there.

one of the issues I am faced with here is as follows.

1. I can not penetrate the roof with a new stack. This leaves me forced to " tap into" the existing stack for venting.

As for the rest of your diag I can follow that very easy. ( I am a visual kind of person)

Thanks again mate!

I got you...

Yes, you can connect the 3" PVC stack into the 4" cast iron stack via an inverted sanitary tee fitting at a minimum of 40"- 42" off the finish floor in the attic.

Be sure when you cut into that stack that you support the weight of the stack using a RISER CLAMP as posted at Speedball's post above. Support the piece going through the roof and be sure the bottom of the stack is supported in some way.

To cut into the 4" cast iron stack, once supported, you will use a sawzall with bimetal blades (or lennox diamond reciprocating sawazall blades if you can find them). You should purchase a 4"x3" NO HUB cast iron sanitary tee fitting here and invert it and connect it to the cast iron stack using shielded/mission clamps or 4 band husky no hub clamps (see images in pic. Below).

You will measure the tee fitting and then add a 1/2" to 3/4" to the measure and transfer that measure to the cast iron stack. Cut the piece out and then slide the clamps onto the pipe. Install the rubber sleeves, flip them back on themselves (see image) and insert the cast iron sanitary tee. Flip the rubbers onto the inverted fitting, slide the clamps in place and tighten up as needed for tight joint!

You need the cast iron wye here as most codes frown on inserting plastic in between cast iron... although not as much a concern on top floor. You can image the issues on the bottom floor... some pretty heavy weight there, so cast iron is simply required... ;)

The cast iron no hub sanitary tee fitting is only available at a plumbing supply store. You will need a shielded mission clamp (cast iron to PVC) to transition from the cast iron to the PVC at the 3" branch of the cast iron sanitary tee.

Back to you...

MARK

Mark,

Quote here "Yes, you can connect the 3" PVC stack into the 4" cast iron stack via an inverted sanitary tee fitting at a minimum of 40"- 42" off the finish floor in the attic."

I do not have that Dimensional height from the finished floor. As the 4" steel vent is in the eve of the attic I have a max exposed steel of 2- 2 1/2 feet. Realistically i will have the 3" set dead center of the steel at around 10-15 inches off the finished floor.

As a side note, My buddy has given me the go ahead to penetrate the roof. So, I can do this as a complete new install. Any diagram you could send would be great. ( I prefer to run all new and tap into the crawl space for my main drain.

Thanks again for reading and helping me.

If you can't connect the wet vent from the lavatory into the vent stack at 42" ish off the finish floor then you will definitely be best to penetrate the roof separately with a 2" vent... ;)

Otherwise, here is the newest drawing... hope this finishes it for you... :) You will penetrate the roof at 12" if no snow in your area, or at 24" if snowy area.

MARK