Plan for garage ceiling insulation

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I think I have my gas line project figured out now onto the insulation project.

I have read a great many of the threads on the subject thus far, but thought I would pass my exact idea by the forum for comments.

A little background info, basic 2 car 20x20 garage, unvented ceiling, no insulation presently, very basic. Obtained a 45k Mr. Heater off CL for a song.

Here we go in order from the underside of the roof deck:
1. 1" iso board adhered to the bottom of the roof deck with the perimeter and any punctures sealed with Great Stuff
2. R38C FG
3. Vapor barrier (10 mil?) across inner edges of roof joists, taped on seams and staple holes
4. 1" foil coated iso board on the inner edges of the roof joists over the vapor barrier with edges and nails taped

Thoughts?

 

[jklingel]

(1)With no venting, I think you need to stick w/ iso all the way, or get it closed cell foam sprayed. Water IS going to get out of the conditioned space, sooner or later. (2) Again with no venting, I'd look real hard at the Airtight Drywall Approach; it will probably meet code for vapor retarding (1 perm, I think it is), and a real vapor barrier may cause serious problems. The roof needs to breathe SOMEWHERE, and the ADA will let it breathe in. True vapor barriers are only suggested in very cold climates; if you are in one, I think I'd still use the ADA in your situation. Check on greenbuildingadvisor and buildingscience.

 

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Thanks for the feedback.

BTW, located in Chicago, so it is definitely cold in the winter.