I also live in Colorado. While using Closed Cell Spray Polyurethane Foam in a Cathedral Vault; you do NOT need to include an "air gap". I understand that if you installed 8" of SPF, a natural 4" air gap would occur. This seems like a good idea, but it's NOT. Spray Polyurethane Foam is a very flammable product, which is why it cannot be left exposed anywhere in a home other than basement or crawl space Boxsills/Rimjoists.(Perimeter of house between floor joists) It wouold be a fire hazard and fail an inspection by a good inspector. SPF always needs to be touching drywall or something that disallows any airspace against it.... UNLESS a flash barrier is installed against it. This can be achieved with spray liquids, facing products, etc. The best thing to do is save money and install a HYBRID system with LESS SPF... filling the rest of the cavity with a fiberglass batt. 6" SPF = (R42) + 6" (R19) batt = R61. Chuck Davis The INSULATION Guys

I also live in Colorado. While using Closed Cell Spray Polyurethane Foam in a Cathedral Vault; you do NOT need to include an "air gap". I understand that if you installed 8" of SPF, a natural 4" air gap would occur. This seems like a good idea, but it's NOT. Spray Polyurethane Foam is a very flammable product, which is why it cannot be left exposed anywhere in a home other than basement or crawl space Boxsills/Rimjoists.(Perimeter of house between floor joists) It would be a fire hazard and fail an inspection by a good inspector. SPF always needs to be touching drywall or something that disallows any airspace against it.... UNLESS a flash barrier is installed against it. This can be achieved with spray liquids, facing products, etc. The best thing to do is save money and install a HYBRID system with LESS SPF... filling the rest of the cavity with a fiberglass batt. 6" SPF = (R42) + 6" (R19) batt = R61. Chuck Davis The INSULATION Guys

I also live in Colorado. While using Closed Cell Spray Polyurethane Foam in a Cathedral Vault; you do NOT need to include an "air gap". I understand that if you installed 8" of SPF, a natural 4" air gap would occur. This seems like a good idea, but it's NOT. Spray Polyurethane Foam is a very flammable product, which is why it cannot be left exposed anywhere in a home other than basement or crawl space Boxsills/Rimjoists.  (Perimeter of house between floor joists) SPF always needs to be touching drywall or something that disallows any airspace against it.... UNLESS a flash barrier is installed against it. This can be achieved with spray liquids, facing products, etc. The best thing to do is save money and install a HYBRID system with LESS SPF... filling the rest of the cavity with a fiberglass batt. 6" SPF = (R42) + 6" (R19) batt = R61. Chuck Davis The INSULATION Guys

I also live in Colorado. While using Closed Cell Spray Polyurethane Foam in a Cathedral Vault; you do NOT need to include an "air gap". I understand that if you installed 8" of SPF, a natural 4" air gap would occur. This seems like a good idea, but it's NOT. Spray Polyurethane Foam is a very flammable product, which is why it cannot be left exposed anywhere in a home other than basement or crawl space Boxsills/Rimjoists.(Perimeter of house between floor joists) It wouold be a fire hazard and fail an inspection by a good inspector. SPF always needs to be touching drywall or something that disallows any airspace against it.... UNLESS a flash barrier is installed against it. This can be achieved with spray liquids, facing products, etc. The best thing to do is save money and install a HYBRID system with LESS SPF... filling the rest of the cavity with a fiberglass batt. 6" SPF = (R42) + 6" (R19) batt = R61. Chuck Davis The INSULATION Guys