I have an attic over a garage that I want to turn into an office/overnight room. The house is inland in San Diego County and temperatures are regularly in the 90s in the summer. There is no insulation in the roof, the 2x4s are exposed, as is the plywood sheathing, and the temperature in the attic in summer is probably as high, if not higher, than the outdoor temperature. The asphalt shingle roof is probably 5 or 6 years old, and was installed over new thick plywood.
My question is this. Should I install insulation between the beams and then either or 5/8 dry wall over the beams, OR put up foil radiant barrier insulation to reflect the summer heat and then dry wall over the foil?
I plan to heat and air condition the space but I would also like to save on energy costs. To help with this I recently installed two Velux opening skylights with solar blinds to replace the leaky fixed units that were installed when the house was built in 1953.
I would appreciate any and all thoughts of how to proceed.