My house was built in 1982 with a lean to porch. I enclosed the porch and now need to insulate the roof on the porch. The ceiling consists of 2 x 6 rafters with open perlin and a metal roof on top. I need to insulate between the rafters but the ceiling is already low and I can't drop it down enough to provide a proper vent space above the insulation.
My thought was to remove the metal roof, add decking and tar paper then 2 x 4 perlins on top of tar paper and then a metal roof. I would then add 6" of insulation between the rafters. Would this give me enough air gap between the roof and insulation? Since this is a lean to porch, there is no way to let air out at the peak of the roof. I live in central Texas and the temp. gets over 100 degrees in the summer. Any advice would be greatly appreciated.