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Roof insulation plan double check

Spenceday | Posted in General Questions on

I recently went back and listened to Martin’s FHB podcast interview and now feel the desire to run my addition roof insulation plan by you guys. I’m in zone 4A, house is a 1953 ranch that I’m remodeling and upgrading insulation throughout.
15’x 14′ addition. Cathedral ceiling, 2×12 rafters with collar ties 18 inches below ridge to create flat ceiling area to place lighting and fan boxes without running into the insulation, 3-4 inches of closed cell spray foam (R-19 target) against roof deck then R-30 Rockwool batt. Drywall ceiling. The roof decking will be OSB or plywood (need to figure that detail out)  then felt and shingles.  Hot roof assembly. 
Am I missing the mark and creating any problems?

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  1. GBA Editor
    Martin Holladay | | #1

    That sounds fine to me. It's a flash-and-batt job with about 39% of the total R-value in the form of closed-cell spray foam. That works in Climate Zone 4A.

    More information here: "Flash-and-Batt Insulation."

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