If somebody used butyl to seal an ac unit to the roof, they didn't have a clue what they were doing. A foam gasket without any sealer is how they install. Also, im 68 years old, I handled and placed these by myself. Intelligent technique. Fogatti has a very poorly designed baffl7ng system, very poor documentaion/instructions, a poor design for the control box location and instead of the inside plenum securing to the unit itself, this lousy design make you screw it to your ceiling. I suspect the engineer that designed it has a bad drug problem.