Installing Slate Roofing on Solid Sheathing - Commercial Roofing Tips
First, you should consider installing a beveled wood cant strip along the eave. This is an optional feature but does help get the starter slate course on the same angle as the rest of the slates. The thickness is the same as the thickness of the slate used. Second, install the underlayment over the roof valleys, hips, and ridges. In climates with heavy snows or rains, double the 30-pound builder's felt underlayment at the eave or use a self-adhering underlayment.
The self-adhering underlayment is a polyethylene film and a rubberized asphalt coating that has an adhesive on the back. In harsh climates extend this eave underlayment at least 24 inches beyond the exterior wall of the commercial roofing project. Then install copper drip edges and rake flashing.
Then begin installing the starter strip and overlap the drip edge 2 inches. Some roofers place the back of the slate up so that the overhanging edge will do a better job of dripping off the water. Since the joints between slates must be staggered 3 inches from the adjacent courses, use a short starter slate that will locate its joint away from that on the first course. Run chalk lines to keep the starter strip and all following courses in line.
The course should overlap the previous one by at least 3 inches to ensure the nails are covered. The slates overhang the eave by 2 inches and the rake by 1 inch. It will be necessary to cut some slates to maintain the 3-inch spacing between joints. Measure ahead and plan for the last slate. It should be at least 4 or 5 inches wide; very narrow end pieces will break and are hard to cut, punch a hole in, and nail.
As the second course is laid, begin with a narrower slate to ensure the 3-inch minimum spacing between joints is maintained.