Venting question- Can I tie two stacks together?

[markcool]

It's me again with my attic remodel.

I'm putting a guest bath above an existing bath. The vent for the 1st floor comes up in the same wall where I'm dropping the stack for the new bath. The old one is 4" cast.

My question is, can I tie these two together once they've passed the flood rim of the highest fixture (the lav, ) so that I have just one roof penetration?

Thanks,

 

[phishfood]

Yes. Make sure that any horizontal piping is at least 6" above the rim of the lavatory, and all will be well.

 

[markcool]

Thanks for the confirmation.