Progress, page 60
Here the underlayment pads are being installed with screws and large washers. The pads are
about one half inch thick and are pretty tough. They do a nice job of bridging cracks and
knotholes in the plywood, as well as providing a bit of insurance against deck nails popping up
over time. The extra insulation doesn't hurt either.
The pre-welded field sheet has flaps on the underside (every five feet where the factory laps were
made) that are used to fasten the membrane to the roof, again with screws and large washers. The
contraption on the right grips both the substrate and the flap on the underside of the membrane and
stretches the membrane prior to fastening ... kind of like a carpet stretcher. After each flap is
secured, the rest of the field sheet is flipped over (right side up) for the next five feet and the
process is repeated.