The project started with no ventilation and two layers of rotting plywood. We removed all of the plywood and installed proper vents because the fiberglass insulation was directly underneath the roof sheathing and would not allow air to freely flow under the roof deck. Installed new plywood and a properly vented roofing system! The Timberline HDZ has a 25 year warranty against blue/green algae and we installed two rows of zinc strips to help prevent moss growth as that was another serious problem that was zapping the life of the shingles.