Adding 5pc bath upstairs. Existing downstairs vent Stack (4" cast) runs upstairs in middle of new bath. Can I 90 the exsisting vent and bring it to back of house (new bath cantilevered off house two feet) and use for waste for new fixtures and run up a separate vent off of that?

My architects plans for wet vent were approved by Town and I have planned 6 inch wall on back of house for this purpose.

thanks