How do you assess flash-and-batt installations?
We have begun to see more Builders and Insulators use flash and batt installation and I am not sure how to assess the R-value of the installation and if the installation actually meets the intent of code and programs. Let me make the case… First premise it that RESNET grade one installation is equivalent to meeting the intent of the code as the code only say that insulation must be installed in accordance with manufacture instructions.
I can assess the R-value of blown foam in a 2×6 cavity so 2” would be the equivalent of R-13 if the foam is 6.5 per inch. If an R-19 6” batt is installed perfectly in the remainder of the cavity (no gaps, voids, but some compression) I know that its R-value is diminished due to the compression of the batt. There is no codified or other method that I am aware of to assess the R-value of an R-19 6” batt that has been compressed to fit into a 3.5” space. The 2009 IECC in footnote “A” of the insulation table tells me that I lose 1 R-value for a half inch compression so in a 2×6 5.5” cavity I get an R-18 but it does not line out how to reduce R-value beyond that, just that R-value is lost. RESNET helps by allowing me to assess the batt as a grade 3 for modeling the performance of the batt in the cavity, due to compression, but there is not a direct link to code which says I would need to fail the installation.
So the question is… If I have a 2×6 5.5” cavity with 2” of closed cell foam and a 6” R-19 batt what is the R-value of the cavity and does it meet the intent of code. As a Rater I believe that it would be correct to evaluate is for the purposes of generating a HERS Index as 2” of closed cell foam and an R-19 grade 3 installation. In my neck of the woods most code officials are requiring Grade one as this level of installation is deemed to be equivalent to manufacture installation.
What do you think?
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