Adding a 5" service duct to basement rooms

sakskc

I have new rooms I am framing in my basement. Can I add registers (one each) to the existing 5" service ducts that service the first floor? These ducts are in between the overhead joist are easy to access.
In other words, can one 5" duct service two registers, or must I add a new 5 "duct to the main trunk to service a basement room?

S Wojo

Marty S.

You won't get much air flow to any of those register trying to split it up like that. Take it back to the main trunk. I never use pipe smaller then 6" unless it's going to a tiny bathroom.