Should we insulate the attic floor or roof where attic contains AC system only?
We have an uninhabited attic space (roof slope too low) that has a high velocity AC system air handler and distribution in attic space with blown in insulation between attic floor joists. Heating is a conventional hot water system with boiler in the basement. The attic is vented with both soffit and ridge vents; attic temperatures currently max out around 125 degrees where we live in southeast Michigan. Here’s the dilemma: air sealing is needed between the second floor ceiling and the attic but the combination of ductwork on top of the attic floor joists, low roof slope, blown in insulation and a fair amount of plywood flooring make access difficult. Plus, the attic needs more insulation since it only has 6″ of cellulose and of course the AC is working against the hot attic air. Given our location, is it better and/or more economical to seal penetrations and insulate the attic floor as best as possible and let the AC system deal with the attic heat, or to insulate the roof and improve attic temperatures?