Question 15
Domain 1: Footings, Foundations, and CrawlspacesAccording to the IRC, where is the use of pressure-treated lumber NOT required?
Correct answer: C
Explanation
The IRC requires preservative-treated wood where framing is exposed to moisture, but it does not require it for all interior framing. Interior studs in an above-grade exterior wall with a vapor retarder are protected from direct moisture exposure, so pressure-treated lumber is not required there.
Why each option is right or wrong
A. Sill plates on concrete foundations
B. Posts embedded in concrete in contact with ground
C. Interior studs in an above-grade exterior wall with a vapor retarder
IRC Section R317.1 requires preservative-treated wood only in locations exposed to decay or moisture, including wood in contact with concrete or masonry and framing members that are closer than 6 inches to exposed ground. Interior studs in an above-grade exterior wall are not in one of those moisture-exposure categories, and the presence of a vapor retarder further limits interior moisture migration, so the code does not mandate pressure-treated lumber there.
D. Wood in direct contact with the ground