Determine the calculated wind speed pressure based on the dynamic pressure formula: P = 1/2 ρ x v^2 where P is pressure in pounds per square foot, ρ is the air density in pounds per cubic foot (lbs/ft3) and v is the air velocity in feet per second (fps). Assume there is a 100 mph wind (146.67 fps) and air has a density of 0.075 lbs/ft3. This is calculated to be 806.7 pounds per square foot.
Determine the maximum designed force a roof can withstand before failure. For instance, assume a residential roof has an exposed surface area of 125 square feet and can withstand 110,000 pounds of force applied to it.
Calculate the maximum force that will be applied to the roof by multiplying the velocity pressure by the exposed roof surface area. This is 806.7 x 125, or approximately 101,000 pounds of force. This means that a roof designed for 110,000 pounds of force should withstand the wind speed.