Question 14
Domain 5: Roof-Ceiling Construction and Attic AssembliesWhat is the minimum required ventilation area for an attic space per the IRC?
Correct answer: A
Explanation
The IRC requires attic ventilation to be at least "1/150 of the attic floor area" unless a permitted exception applies. This ratio provides the minimum net free ventilating area needed to reduce heat and moisture buildup in the attic space.
Why each option is right or wrong
A. 1/150 of the attic floor area
IRC Section R806.2 requires enclosed attic spaces to have cross-ventilation with a minimum net free ventilating area of 1/150 of the area of the vented space. The code allows a reduced 1/300 ratio only when specific conditions are met under R806.2 Exception 1, so absent those facts the baseline minimum is the 1/150 calculation.
B. 1/300 of the attic floor area when a vapor retarder is installed
C. 1/500 of the attic floor area
D. No minimum if the attic is unoccupied