During a framing inspection, you notice that the contractor has used 2x4 studs at 24 inches on center for a load-bearing wall supporting two floors. What does the CBC typically require for this application?
Correct Answer
D) 2x4 studs at 16 inches on center maximum
For load-bearing walls supporting two floors, CBC typically requires 2x4 studs at 16 inches on center maximum to handle the increased loads safely.
Why This Is the Correct Answer
The California Building Code (CBC) prescriptive framing requirements specify that load-bearing walls carrying loads from two or more floors must use studs spaced no more than 16 inches on center when using 2x4 members. Tighter stud spacing (16" o.c.) is required because the increased cumulative load from two floors exceeds the capacity of 2x4 studs at 24" spacing. The 16" o.c. maximum is the standard prescriptive limit for multi-story load-bearing applications.
Why the Other Options Are Wrong
Option A: The existing framing is acceptable
The existing framing is not acceptable. 2x4 studs at 24" o.c. may be permissible for single-story load-bearing walls or non-load-bearing partitions in some applications, but supporting two floors demands closer spacing to safely transfer the increased loads to the foundation.
Option B: 2x6 studs at 24 inches on center
While 2x6 studs at 24" o.c. would provide greater load capacity, this is not the standard CBC prescriptive remedy. The code path for this specific condition is to reduce stud spacing to 16" o.c. with 2x4 studs. Using 2x6 studs might be an engineering solution but is not the prescriptive code requirement being tested.
Option C: 2x4 studs with additional blocking
Adding blocking to 2x4 studs at 24" o.c. does not address the load-transfer deficiency. Blocking serves purposes such as fire stopping, lateral bracing, and attachment backing — it does not compensate for inadequate stud spacing under vertical loads.
Memory Technique
Remember: '2 floors = 16 inches.' When a wall carries two stories, the stud spacing drops to 16" o.c. Think of it as the load doubling, so the spacing tightens. The phrase 'Double Load, Double Frequency' (16 = more frequent than 24) reinforces the concept.
More California Questions
A contractor is installing shear walls in a residence located in Seismic Design Category D. The engineer's plans call for 15/32-inch structural sheathing with 8d nails at 6 inches on center at panel edges. The contractor wants to substitute 7/16-inch OSB with the same nailing. Is this substitution acceptable?
You are reviewing plans for a mixed-use building where the ground floor will house a restaurant with commercial kitchen equipment. The architect has specified standard residential electrical requirements throughout. What Title 24 compliance issue should you identify?
According to CBC seismic provisions, what is the concept behind the 'strong column, weak beam' design philosophy?
A residence in California has 2,800 sq ft of conditioned space. The HVAC system efficiency is 16 SEER. What is the approximate Title 24 compliance margin compared to the minimum 14 SEER requirement?
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During construction of a basement in sandy soil conditions, you encounter groundwater at 4 feet below grade. The basement extends 8 feet below grade. What is the critical design consideration per CBC?
During a seismic retrofit project, you discover that existing concrete has a compressive strength of 2,200 psi. The engineer specifies new anchor bolts that require 2,500 psi minimum concrete strength. What is the most appropriate action?
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You're reviewing plans for a wood-framed structure in seismic design category D. The project calls for a shear wall with 15/32-inch structural sheathing and 8d nails spaced 6 inches on center at panel edges. What is the allowable shear value per the CBC?
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