Asphalt shingles comprise the largest segment of steep slope roofing. They are composed of fibrous glass mats impregnated with asphalt. Because asphalt is easily degraded by UV exposure, a surfacing of varying colored mineral granules is embedded into the exposed side of the asphalt shingle that also imparts its finished color. Shingles are overlapped and secured by nailing through the roof overlay of felts or roof paper into the roof deck from the bottom of the roof slope to the high point of the roof referred to as the ridge. Special ridge vents are usually installed to provide ventilation from the attic space. Warranties for shingle roofs range from 10 to 50 years.