When my packaged a/c was installed on the roof they used ductwork that has
a thin layer on insulation inside. But then because of leaks they tarred
the outside. Of course the black absorbs the heat and warms the air
considerably.

How best to insulate? I see the various foam insulation boards. A neighbor
suggests going all out with 2" thick. I see you cut with a circular saw. I
see you tape the joints with 2-7/8" Weathermate Construction Tape. But the
Styrofoam sheathing can only take the UV for 90 days. I have to cover it
with something, either white or reflective. What do you all suggest?

I once got an estimate from a local roofer. He wanted $3500 for like 1/2"
thick insulation. No way should it cost that much. But I don't how he was
going to do the job.

Don. www.donwiss.com (e-mail link at home page bottom).