Performing the framing for a ceiling fan on I-joists is best
Ceiling fans do not require specialized framing for hanging, simply a solid support that stays that way when subjected to years of vibration. The most common method for framing an I-joist for a fan is to create another "I" shaped support above the ceiling. This framing houses the junction box in the center, and serves as the central anchor point for the entire assembly. It's best to do the framing while the ceiling is open and free from obstructions.