Glossary
Attic ventilation
Balanced intake and exhaust openings that let outside air move through the attic, carrying heat and moisture out.
In practice
IRC R806.2 sets a minimum net free ventilating area of 1/150 of the vented space, reducible to 1/300 only under two simultaneous conditions. Poor ventilation is the honest answer to a large share of "why did my roof only last 15 years" questions.