APA - The Engineered Wood Association
Like all construction materials, APA Rated Sheathing panels must be installed correctly to insure best performance. Nearly all roof sheathing complaints are due to incorrect installation. Always check for level nailing surface. This can be done with a piece of lumber (6 feet to 10 feet long) or a long carpenter's level. Trusses or rafters should be shimmed as necessary to provide a level nailing surface. Provide roof ventilation according to building codes.