According to the California Building Code (CBC), what is the minimum depth requirement for continuous footings supporting wood frame construction in areas with freezing conditions?
Correct Answer
A) 12 inches below the undisturbed ground surface
CBC Section 1809.4 requires continuous footings to extend at least 12 inches below the undisturbed ground surface in areas subject to freezing. This California-specific requirement ensures adequate frost protection while being less restrictive than colder climate requirements found in other states.
Why This Is the Correct Answer
CBC Section 1809.4 requires continuous footings to extend at least 12 inches below the undisturbed ground surface in areas subject to freezing. This is California's frost-depth requirement — less stringent than colder northern states because California's freezing areas are limited and shallow, but still requires footings to be below the frost line to prevent frost heave.
Why the Other Options Are Wrong
Option B: 30 inches below the undisturbed ground surface
30 inches is a typical frost depth requirement for colder northern states (e.g., Michigan, Minnesota) where frost penetrates much deeper. California's milder climate, even in freezing areas, does not require this depth.
Option C: 24 inches below the undisturbed ground surface
24 inches is a common footing depth in moderate-climate states. It exceeds California's 12-inch minimum and would apply in areas with deeper frost penetration than California typically experiences.
Option D: 18 inches below the undisturbed ground surface
18 inches is between the correct answer (12 inches) and more stringent requirements. It is a plausible distractor but does not correspond to the CBC Section 1809.4 minimum for California's freezing condition areas.
Memory Technique
12 inches = 1 foot = California frost depth. Remember that California is a warm state — even its 'freezing areas' are at the mild end. One foot down keeps you below the frost line in California. Think: 'Cali frost = one foot, not three.'
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