Metal Roof over existing Shingle Roof
Roof underlayment was installed during initial inspection to prevent rain water from leaking in where missing shingles were blown off during severe thunderstorm. Furring strips are installed at 3 ft spacing, nails with 3 in (12P) ring shank nails at the rafters (24 in spacing o.c.). This provides air gap for extra insulation, as well as, a solid dense lumber for the large panels to be fastened to instead thru the shingles to the roof decking (OSB), which doesn't hold as well. During another strong wind storm, the right gust of wind can rip theses wind sails right off with screws in the OSB decking. Screwed to solid pine, ring shank nailed to soled 2x8 rafters stand much greater wind resistance. Almost double.