Garage ceiling that won't trap moisture

[yimbo]

Going to insulate my ceiling with 6" of craft face fiberglass between 2' on center 2 x 4s strung between the rafters. I want to put some kind of covering on the ceiling to reflect light that won't cause a moisture problem during the winter heating season. I chose to insulate the ceiling instead of the bottom surface of the tin roof to keep from heating the entire upper space, my trusses are 5/12 pitch x 34' long. The fiberglass is much cheaper than the foil bubble foil they put under the tin. The 2 x 4s are going to be up in between the bottom cord of the trusses and the trusses are on 8' centers. Also concerned about the wieght on the truss if I use drywall or plywood. Any suggestions would be apreciated. Thanks

 

[Poppa Bud]

I'm thinking about using 1" thick 4x8 Celotex sheets. Light weight, one side has silver facing for light and heat reflexion. I also plan to use aluminum tape over the joints to make it a little more airtight and give a little more finished look.

Anyone else ever used this?

 

[Gary S]

I used 1" high density foam foil faced insulation on my ceiling. The foil does a nice job of reflecting both light and heat.
And, 1" of that adds another R6 to the ceiling.