I would like to insulate my steel barn roof. Would it be okay to cover the joists completely or is it better to go between them?
Answer:
Either way is acceptable, but you will get better performance by placing the reflective insulation on the bottom of the trusses. That’s because the entire roof area will be covered with insulation, whereas by attaching to the purlins (between the trusses) leaves the trusses uncovered.