Among the many reasons to give residential attics a properly balanced ventilation system of intake vents (in the soffit or low on the roof) and exhaust vents (at or near the roof peak), is the impact it can have on the life of a shingle.
Research by Joseph Lstiburek, Building Science Corporation, Westford, Mass., sites a 10% service life reduction on shingles installed above unvented attics. When I share that statistic with the roofing pros in the audience of our best practices in residential attic ventilation seminars, eyebrows begin to raise, followed by comments such as, “Are you sure the number isn’t higher?” and “Based on my experience that number sounds too low to me.”