For a 2,400 square foot roof in a hurricane zone, if the code requires 45 psf uplift resistance and safety factor of 2.0, what total uplift force must the roof system resist?
Correct Answer
C) 216,000 lbs
2,400 ft² × 45 psf × 2.0 safety factor = 216,000 lbs total required uplift resistance.
Why This Is the Correct Answer
Total required uplift force = Area × Uplift pressure × Safety factor = 2,400 sq ft × 45 psf × 2.0 = 216,000 lbs. The safety factor of 2.0 doubles the calculated uplift load to provide a structural margin against the extreme wind events that characterize Hawaii's hurricane zone.
Why the Other Options Are Wrong
Option A: 54,000 lbs
54,000 lbs comes from applying only part of the formula — likely 2,400 × 45 ÷ 2 rather than × 2. This is a critical sign reversal: the safety factor multiplies (makes the design requirement larger), it does not divide.
Option B: 162,000 lbs
162,000 lbs does not correspond to a correct use of the given values. It may stem from using 1.5 as the safety factor instead of 2.0 (2,400 × 45 × 1.5 = 162,000), substituting an incorrect multiplier.
Option D: 108,000 lbs
108,000 lbs equals 2,400 × 45 = 108,000, which is the base uplift force without the safety factor applied. This is the most common error — forgetting to multiply by the safety factor.
Memory Technique
Safety Factor = Safety Net Below You. A safety factor always makes the number bigger (the net must hold more than your weight). Multiply, never divide.
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