Question 28
Domain 1: Footings, Foundations, and CrawlspacesAccording to the IRC, what is the minimum size of a footing for a one-story wood-frame building on soil with 2,000 psf bearing capacity?
Correct answer: B
Explanation
The IRC prescribes a minimum footing width of 12 inches for one-story light-frame construction on soil with 2,000 psf bearing capacity, and the footing thickness is commonly taken as 6 inches for a standard concrete footing. This matches the code’s prescriptive footing dimensions for that soil condition and building type.
Why each option is right or wrong
A. 10 inches wide x 6 inches thick
B. 12 inches wide x 6 inches thick
IRC Table R403.1(1) sets the prescriptive footing width for a one-story light-frame building on soil with a 2,000 psf presumptive bearing capacity at 12 inches. The footing must also be at least 6 inches thick under IRC R403.1.1, which governs minimum concrete footing thickness, so the required minimum size is 12 inches by 6 inches.
C. 15 inches wide x 6 inches thick
D. 18 inches wide x 8 inches thick