3. Screw Down Underlayment
The sheet-rubber roofing material that Tom is using requires a substrate called iso board—½-inch-thick rigid foam (made of polyisocyanurate) with a special fiberglass backing. The iso board (a flat version of the same material he orders custom-fitted for larger roofs) cuts easily with a utility knife and anchors to the plywood sheathing with screws and large galvanized steel washers. It provides a soft, protective base for the rubber. Tom makes sure to stagger the joints and to fit the pieces tightly against each other, as iso board doesn’t expand and contract like plywood
Got my elastomeric roof and love it because it’s so easy to fix. I still have a bunch of holes to cut into the roof for a stove and lights. Already put lots of holes in it when I put the solar panels on the roof. There’s nothing like being able to fix a roof easily myself.