Question 22
Domain 3: Floor Construction and Supporting FramingHow must doubled floor joists be connected per the IRC?
Correct answer: B
Explanation
The IRC requires doubled floor joists to be fastened together so they act as one member. Standard practice is to nail them "with 10d nails at 16 inches on center at top and bottom," which provides the required connection and load sharing between the plies.
Why each option is right or wrong
A. With construction adhesive only
B. Nailed together with 10d nails at 16 inches on center at top and bottom
IRC Section R502.6 requires floor joists that are doubled to be fastened together so they function as a single member, and the prescriptive fastening detail is 10d nails spaced 16 inches on center along both the top and bottom edges. That specific nailing pattern is the code-recognized connection for built-up joists in this context; other fastening methods would need to be justified by an approved design.
C. With metal straps every 4 feet
D. No connection required if they are bearing on the same support