I joist questions – GreenBuildingAdvisor

I-joists only need to be attached together if they are side loaded (ie stair opening), if it is just holding up extra weight, you don’t need to do anything.

My suggestion would be to bump it up to the 3.5″ flange ones and go for 16″ OC. The wider spacing makes everything easier (ie tools fit, fans fit, ducts fit, standard insulation). Usually the cost delta between the two is not much.

Also make sure you plan out your HVAC ducting, sometimes you need a 2′ chase to run a supply trunk, easy now, very hard later.