The Owens Corning warranty covers defects. Maintenance covers the rest.

• Improper or inadequate ventilation or drainage, including unvented attics and enclosed rafter assemblies.
• Foot traffic and falling objects, such as tree branches landing on the roof.
• Debris, resins and drippings from trees and other foliage.
• Changes after installation, including power washing, painting, and cleaning solutions that don't follow Owens Corning's algae removal instructions.

The standard warranty also leaves out leaks from other manufacturers' pipe boots and problems from non-Owens Corning items, like a chimney with cracked mortar. In some coastal or low-rainfall areas, it notes that copper from algae-resistant shingles can corrode aluminum gutters.

None of that is a manufacturing defect. Most of it builds slowly, out of sight from the ground, and the homeowner finds out when something leaks.

• A yearly look at the whole roof. Owens Corning lists annual checks of the shingles, flashing, roof edges, gutters and attic, and a professional inspection when there are concerns or the roof is aging.
• A pro checks ventilation before winter. Owens Corning tells homeowners to have a roofing contractor check attic ventilation and insulation, which lowers the risk of ice dams.
• An inspection before hurricane season, in hurricane-prone areas, for loose or cracked shingles, damaged flashing and a damp attic.
• Call a contractor for anything on the roof: steep or hard-to-reach roofs, damaged shingles or flashing, and moss, algae or leaks that keep coming back.