Is this true? should the AC unit just sit on the roof and be mounted to the roof via the duct work and not the stilts mounting hardware? I have a Trane AC unit that is ontop of my roof. The roof has a slight angle to it.. maybe about 10 degree. I just had the roof shingles replaced as the roof was leaking and the roofer was good enough to lift the AC unit and re-roof the section under the AC unit. Job is done roof is great, but the AC unit is no longer mounted to the roof. The AC unit sits on a metal stilt stand and the stand is what makes contact on the roof. The stand has mounting holes but the roofer says its not to be mounted otherwise the roof will leak where the stilts are mounted to the roof and that the AC unit is held in place by the ductwork. Is this true? should it just sit there and be mounted to the roof via the duct work? Note: I live In California, we do have earthquakes from time to time here.