Calculate the required roof uplift resistance for a 2,000 sq ft residential roof in Hawaii's hurricane zone with a 150 mph wind speed requirement. Use uplift pressure of 45 psf.
Correct Answer
A) 90,000 lbs
Total uplift force = roof area × uplift pressure = 2,000 sq ft × 45 psf = 90,000 lbs total uplift resistance required.
Why This Is the Correct Answer
The calculation is straightforward: Total uplift force = roof area × uplift pressure = 2,000 sq ft × 45 psf = 90,000 lbs. The 150 mph wind speed information is contextual (it determines the 45 psf value) but is already factored into the given uplift pressure. Multiplying the area by the pressure gives the total force the roof structure must resist.
Why the Other Options Are Wrong
Option B: 112,500 lbs
112,500 lbs would result from multiplying 2,000 × 45 × 1.25, incorrectly applying an additional factor of 1.25 that is not specified in the problem. This suggests a misapplication of a safety factor or misreading the calculation.
Option C: 135,000 lbs
135,000 lbs would result from multiplying 2,000 × 67.5 — essentially using an incorrect uplift pressure of 67.5 psf instead of the given 45 psf, or from incorrectly combining the 150 mph wind factor multiplicatively rather than using the provided 45 psf directly.
Option D: 67,500 lbs
67,500 lbs would result from calculating 1,500 sq ft × 45 psf or 2,000 × 33.75 — a common error from misreading the roof area or applying half the pressure. This answer is exactly 3/4 of the correct answer, suggesting a partial area or rate error.
Memory Technique
F = P × A (Force = Pressure × Area). This is the fundamental load calculation formula. When the problem hands you pressure (45 psf) and area (2,000 sq ft), just multiply: 2,000 × 45 = 90,000 lbs. Do not over-engineer it.
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