Ineffectiveness of increasing R-value with more than 4 in. of closed-cell spray foam?
I have been told a number of times that using more than 4" of cc spray foam (in a wall or roof assembly) has little value at increasing r-value. In other words, does using more than 4" not have a linear increase in r-value? The reason I ask is b/c I need the recommended r-35 against the bottom of my roof sheathing (with blown-in cellulose in the remainder of my cathedral truss) to prevent the roof sheathing to dip below the dew point and create condensation. Any thoughts? Thanks.
Posted Feb 2, 2013 7:27 PM ET
Edited Feb 4, 2013 7:55 AM ET
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