# How to calculate wind loads on roofs

Written by doug leenhouts
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The force that winds apply to a roof can be calculated using a system of coefficients. These values represent the type of roof, the type of building, the directionality of the wind, the exposure of the roof to the wind and numerous other factors. Once calculated, the force can be used to influence the materials selected for the roof so it cannot be torn from the building in strong winds. Additionally, it can influence decisions regarding the placement of rooftop equipment, including solar panels.

Skill level:
Moderate

• Calculator
• Tape measure

## Instructions

1. 1

Measure the height and width of the roof using a tape measure. Keep the units in feet so you do not have to convert it later.

2. 2

Determine the maximum wind speed in miles per hour.

3. 3

Assume there are no extraordinary factors, such as an abnormal topography, wind directionality or building importance level. The importance level takes into consideration the consequences of failure, including loss of life, along with social and environmental consequences.

4. 4

Reference the wind pressure tables for various roof heights and wind speeds. This can be found on Cornell University's website or in an engineering textbook. For example, the wind pressure on a roof 45 feet high in 70mph winds and at an exposure level D, per the Universal Building Code of 1997 method, is 9.39 Kilogram per square foot.

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