Flat Roof Replacement, Replaced all old sheathing and re-enforced rafters Installed new 4′ x 8′ 3/4 sheathing over the entire rafters and Installed new PVC Flat Roof Drain too eliminate severe water from holding on back wall of flat roof. Installed new 1/2″ Insulation and new fiberglass base sheet and new Firestone App 160 Modified Rubber Roof over the entire working areas on flat roof surface and wall flashings.