Proper ventilation is one of, if not the most important key factors in the life expectancy of a roof. Depending on the type of roof and its slope, asphalt roof requirements can range from 1sq. ft. of ventilation for every 300 sq. ft. up to 1 sq. ft of ventilation for every 150 sq. ft. Metal roofing systems installed by LEMM use ridge venting as a standard, which is the most effective venting system for your home.