Why is it some roofers use a blowtorch to heat rubber membrane roof material for a flat roof installation with no adhesives when the instructions I located via Google reveal the following:
". . . Smaller width pieces are often used for residential work. They are easier to handle and there are special adhesives, solvents, and tapes that assure leak free performance at the seams. These membrane roofing systems also permit you to upgrade your house insulation. You can install high performance insulations on the roof deck before the membranes are applied. Often a thin one half inch thick fiberboard sheet is placed on the insulation or roof deck before the single ply membrane is attached. . . . ."
Mike