During a building inspection, you discover that the contractor used 2x4 studs at 24 inches on center for an exterior bearing wall in a two-story residence. According to CBC, what is the verdict?
Correct Answer
B) Acceptable for second story only
CBC allows 2x4 studs at 24 inches on center for the second story of a two-story building, but the first story bearing wall requires 2x6 studs or 2x4 studs at 16 inches on center due to increased load.
Why This Is the Correct Answer
CBC permits 2x4 studs at 24 inches on center in the second story of a two-story bearing wall because the load above is limited to the roof and second-floor structure. The first story, however, carries the additional weight of the second story, roof, and all live loads, requiring greater capacity — either 2x6 studs or 2x4s at a closer 16-inch spacing.
Why the Other Options Are Wrong
Option A: Acceptable for first story only
2x4 at 24 inches on center is not acceptable for the first story, which bears the full cumulative structural load. The first floor requires 2x6 studs or 2x4s at 16 inches OC to handle the increased demand.
Option C: Not acceptable for either story
'Not acceptable for either story' overstates the restriction. The code specifically permits this lighter framing configuration for the second (upper) story where loads are lower.
Option D: Acceptable for both stories
'Acceptable for both stories' is wrong because the first story has higher loads requiring heavier framing. Allowing 2x4 at 24 OC throughout both stories would violate CBC for the lower story.
Memory Technique
Second story = lighter load = lighter framing allowed. Think: 'Top gets 24, bottom needs more.' The second story is on top — it carries less — so the looser 24-inch spacing is permitted there.
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