Hello,

I live in Northern Virginia and I am at the stage of my home addition where I have to make a decision on insulating my attic (R-38). I have read quite a bit and know there are clear advantages of various types with the balance favoring blown in cellulose. My house is in town and small and I need the attic space for storage. No way around it, so cellulose in the attic floor won’t work in my case unfortunately. My plumbing and geothermal air-handler are also in the attic space, once again due to size constraints. I am a believer in attic ventilation and have soffit and ridge vents. It seems my choices are foam or batt or combination. I knohave w I have to be careful about vapor barriers and that has led to more confusion and consternation… I was thinking about the best way to handle my situation and wanted an opinion on my thoughts…
My roof is at about a 39 degree slope, the rafters are 2×8 and 2×6 prefab trusses. I was thinking about using foil faced 2″ rigid foam insulation (R-13) in between the rafters with a 1″ airspace gap from the sheathing for ventilation. Then I was going to have a spray foam contractor seal the underside of the insulation board with open cell insulation. If I add a layer of Prodex foil faced polyethylene between the rigid foam board and the airspace (on top of the foam board prior to putting them between the rafters while maintaining my airspace for ventilation), I can significantly reduce my spray-foam costs, meeting my R-38 requirement with 5″ of open-cell. I vaguely remember reading something about open cell foam at 5″ or less not requiring the fire retardant coating but I haven’t been able to find any reference to verify this notion. I am largely concerned about vapor barriers and making condensation problems with this scheme. Any thoughts on this plan or a recommended solution to my situation would be greatly appreciated. Best regards from Virginia.