Checkpoint One After tear-off
Every shingle and all the debris comes off first. Then the decking is inspected properly, board by board: gaps wider than a quarter inch, delaminated plywood, and rot. Owens Corning's installation instructions call for a deck of boards at least 6 inches wide, plywood at least 3/8 inch or OSB at least 7/16 inch, spaced no more than a quarter inch. Where a gap runs wider, we repair or replace the boards. Rot we find is photographed before it's replaced. What we are confirming is that the decking is a solid nailable surface the new roofing system will fasten to and hold to. The entire deck is photographed before any underlayment goes on.