Adding a new 1/2 bath, just a sink and a toilet. The vent for the sink (1 1/2") and the vent for the toilet (2") will join together in the attic and then exit the roof. These vents are not tied in to any other vents in the house. Can this vent exit the roof as 2" or does it need to be increased to 3" before protruding. No inspection in this town, however, I do want to do it correctly.