What is the minimum nominal dimension lumber that can be used for a sill plate in wood frame construction per CBC?
Correct Answer
D) 2x4
CBC allows 2x4 minimum for sill plates in wood frame construction, though 2x6 is often used for wider walls or when additional anchorage is required.
Why This Is the Correct Answer
2x4 is the minimum nominal dimension allowed for sill plates in wood frame construction under CBC. The sill plate transfers loads from wall framing to the foundation and must be anchored with bolts, but CBC does not require a width greater than 2 inches nominal thickness and 4 inches nominal width as the starting point.
Why the Other Options Are Wrong
Option A: 2x10
2x10 is a much larger member than required and is not the minimum. While 2x10 lumber is commonly used for floor joists and rafters, specifying it as a sill plate minimum would be an over-design. The CBC minimum is far smaller.
Option B: 2x8
2x8 exceeds the minimum requirement for sill plates. Though some applications (like wider walls or specific anchorage conditions) may use 2x8, the code does not mandate it as a baseline minimum for standard residential sill plates.
Option C: 2x6
2x6 is commonly used for exterior walls and wider sill plates but exceeds the CBC minimum requirement. Many builders choose 2x6 for better anchorage or to match 2x6 wall framing, but the code minimum remains at 2x4.
Memory Technique
The word 'minimum' is your clue: go as small as the code allows. '2x4 = the foundation of framing' — just as a 2x4 stud is the basic building block of walls, a 2x4 is the basic minimum for a sill plate. Everything larger is an upgrade, not a requirement.
More California Questions
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