Why Is it Important to Ventilate?
A balanced ventilation should be a top priority. With this system, wind flowing over the roof ridge creates a negative pressure and draws warm air from the attic. Cool air enters through a properly ventilated soffit system that cools the roof and exits through the roof, gable or ridge vents. Even on calm days, the natural ability of warm air rising maintains a continuous airflow all year with no energy consumption or mechanical parts.
Normal building code requirements for ventilation or net free areas (NFA) – the total unobstructed area through which air can enter or exit with a non-mechanical ventilation system – are as follows: Minimum NFA of one square foot of ventilation for every 150 sq. ft. of attic floor space.
OR
A minimum NFA of one square foot of ventilation for every 300 sq. ft. of attic floor space, if: 50%-80% of the required ventilation area is provided by vents located in the upper portion of the space to be ventilated at least 3 feet above the eave/soffit vents with the balance of the required ventilation provided by an eave or cornice vents. (2000 Michigan Residential Code)
OR
Minimum NFA of one square foot of ventilation for every 300 sq. ft. of attic floor space, when a vapor barrier of 1 perm or less is installed on the warm side of the ceiling.