Is six inches of open-cell spray foam enough for Climate Zone 3A attic?
I am (mildly) renovating a circa 2006 three-level townhouse and trying to be prudent with the budget. On Friday the HERS rater completed a blower door test, and we met with an HVAC/Energy Performance contractor we have both worked with on a previous house. So far we have a general plan for air sealing the home’s more significant air leaks.
I am less comfortable with our initial discussion on how to improve the townhouse’s attic insulation and would value the GBA community’s input.
The HVAC/Energy Performance contractor is suggesting converting the attic to a semi-conditioned space and installing six inches of open cell foam. (The conditioning will be done by a new five-speed heat pump that also has a dehumidification feature. Service to the third floor is provided by ducts in the attic. A second system services the first and second floors.)
I questioned the amount of insulation since that will be far short of current recommendations for Zone 3A. But both the rater and contractor advised that installing R-38 would not be cost-effective and anything beyond six inches would offer diminishing returns.
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