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Conditioned attic approach – open cell & Rockwool?

ronzmac | Posted in General Questions on

Hello all,

I’m building a new home and will be doing a conditioned attic space.

I’ve done a little reading about conditioned attic spaces and some notes I’ve jotted down include:

* Since I’m in climate zone 2, it’s recommended that open cell foam be used for the rafters.  I heard OCF is “breathable” and acts as an air sealer.

* I’ve read about “flash and batt”, but it appears this usually involves closed cell foam (not open cell foam).

* I heard you want to try to get around R-38 in your attic in this climate zone 2.

* Rockwool is fire resistant.

My rafters are 24” OC, 10” deep.

Assuming the notes I jotted down are true, I was thinking about doing 6” OCF and 4” Rockwool batt (maybe blown in mineral wool?),  I believe this will get me close to r-38 in the attic rafters. 

Does anyone see problems doing a “flash and batt” with this configuration?   I don’t know enough about the physics of either product so thought I’d ask a group who is much smarter about this stuff.

Thanks for your thoughts.


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