I built a "sleeping porch" for three seasons. It has a very low pitch with 2x6 rafters and I used a rubber glue down roof.
The question: I would like to reflect off the heat generated by the black rubber roof to make it bearable in the summer. Can I tack 1/2" foil faced isocyanate foam boards directly to the ceiling and then cover with drywall? There is a soffit for ventilation and this connects to the garage attic.
John- Yes you can, however my feeling is that it may not offer all that you hope for in limiting the heat transfer. I would do it and as well, add some venting at the top so that air can pass from soffit to peak....as it were. Your soffit vents let air in but not out. The other option is mechanical venting.