Why do you only recommend closed cell spray foam insulation in attics?
Because open cell spray foam on a attic roof deck off -gasses, does not stop heat vapor, and rots out the roof if there is a leak you never see. Closed cell foam will seal off a leak, does not absorb heat vapor nor off-gas as it heats up. When a roof deck is scanned with an infrared heat gun where the attic fan was left in place and foamed over, the open cell foam glows yellow with heat and the metal fan glows red. Closed cell foam stays blue with no heat infiltration and it is a vapor barrier. It adds strength to the attic for protection against wind and has been used on flat roofs as a water proof coating.