[CarGuys]

There is a long thread on this in Contractors and Services.

The bottom line is the roofing associations after years of study had or found no negative effects on the shingles. Steel Tile or Asphalt

Now you will find from Wayyyyyyyyyyyyyyyyy back some concerns but that was years ago when the barrier was incorrectly applied against the roof,

Now a professional contractor has it installed and suspended below the roof using the rafter studs. Heat comes through the roof and the natural convection currents carry it up and out your standard roof vents installed per code. Thus no power vents necessary.