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Using Spray Foam to Create Unvented Attic

Josh_Seidman | Posted in GBA Pro Help on

Leaky house, 7244 CFM 50.  Climate zone 4.  After blower test, recommendation was to create unvented attic spaces (3 attic spaces total each connected via knee wall and accessible via doors from second floor living space)  using open cell spray foam.  I have HVAC equipment located in one of the attic spaces and plenum running throughout all the attic spaces.  But these are AC only (no heat pump.)  Many articles about resolving humidity issues by conditioning the space should humidity occur after creating the unvented space.

Seems i could address any humidity issues in summer by adding supplies from my AC in the attic spaces.  But my heating system seems to be quite unique and so not sure i could heat the attics in the winter should there be moisture issues during the cooler months.  My first floor heating is via boiler with hydronic radiant heating that runs in the first floor ceiling (which is essentially the attic flooring!)  Currently insulation under attic subfloors to “keep” most the radiant heat directed to the first floor so intent is to leave this insulation in place.  The second floor has livable space and is heated via wall radiators.  The second floor connects to our attic spaces via full size doors so some leakage thorough each door.   So the only way to “heat” the attics (should moisture occur) is via indirect air leakage.

Based on above information, should i create an unvented attic?  Or am I going to cause issues that I later cannot resolve?  Any recommendations or advice is greatly appreciated.

Thanks in advance!

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