ASHRAE 62 requires 100 cfm per car. What size of openings could provide that, assuming one uses natural ventilation?
Two documents that address natural or passive ventilation in garage door space are the International
Mechanical Code (IMC) and ASHRAE 62 which is also referenced in the IMC. The general
requirement is 100 cubic feet per minute per vehicle allocation within a garage space; however, a
comment based in ASHRAE 62 reads that garage space air ventilation requirements are “normally
satisfied by infiltration or natural ventilation.” In actuality, the garage door opening itself can be
considered a “natural vent” not only because of its obvious capability of opening and closing but also
because its area is usually more than 4% of the area of the affected garage space. Therefore, vents in
garage doors should not be needed for natural or passive ventilation.
**** I would check on what the local codes require.