Does anyone know how to adjust for icynene spreay foam insulation in a
sealed attic space - closest option seems to be to select R-19 batt on the
underside of the roof deck, but this isn't very accurate because icynene in
a sealed attic provides a significantly better performance than just R-19 on
underside of pitched roof?
Thanks,
Joe Snider, AIA, LEED AP
Icynene is hot stuff because it's also an air barrier.
I reckon if you define an appropriate R-value for your icynene/joist
layer and another continuous layer for anything beyond, you should be
able to account for the air barrier seal by ensuring there's zero
infiltration through that construction. Infiltration is handled at the
space and/or construction levels depending on the method you're using to
define it... best I can say is to look into it.
Maybe I'm underthinking it, but I think that's all you should need to do
to demonstrate a difference against batt - pay attention to you
infiltration inputs.
NICK CATON, E.I.T.
Additionally, in the detailed mode you can change the insulation values
to whatever you feel is appropriate for your situation.
David A. Bastow