Q. A two-story house I’m working on has a zoned air-conditioning system with ductwork running through the hot attic, and the A/C can’t keep the upstairs zone cool on hot, sunny days. What’s the best way to cool that attic space down — add gable vents to the existing soffit and ridge vents setup, insulate between the rafters, or apply a radiant barrier foil under the rafters?

A. Danny Parker, research scientist at the Florida Solar Energy Center, responds ...