This is follow up question to lazypup's response in an old post from 2006 called: Devloped Length of Vent

"Keep in mind that in regions that are subject to frost closure you may reduce the size of the auxillary vents as described until you get into the attic space but the line must then be increased to 3" diameter at least 1' inside the structure before penetrating through the roof. (Some local codes require 4" for frost closure.) " -lazypup

Basically, I have a 1.5" vent stack going through the roof for a 1/2 bathroom and I would like to add a shower and increase the vent size to 2". Would this be an acceptable method without disturbing the current 1.5" vent penetrating the roof deck?

This post was edited by Construction_Zone on Tue, Nov 18, 14 at 15:41