A professional roofing contractor has to take into account the average wind speed in the area to make sure they are building a roof that can withstand it. This is especially important if the wind speeds are high and the building is tall.
Wind speed can give an architect, an engineer, or a contractor an idea about the wind’s potential for damage. They are usually measured at a point 33 feet above the ground, as reported by the National Weather Service. The average speed of the wind is better reflected by its sustained speed. To find the peak wind speeds sustained at short times, 3-second gusts are measured. To measure the wind speeds of a hurricane, 1-minute sustained winds are reported.
The force that a structure has to resist is called the wind load on that structure. Wind speeds are commonly measured for their potential for damage, but a building’s wind load can vary from those speeds by over 30%.
There are different factors that can influence a structure’s wind load. For example, the wind load on a building’s shape and its orientation relative to the direction of the wind. The density of the air plays a part, as well. The building’s location has a specific Wind Exposure Category, and that can influence wind load too.
Determining Damage to a Roof
Wind load is a more exact determining factor when it comes to wind damage on a roof installation, as wind load directly applies to the forces exerted by the wind on the roofing structure. There are three types of wind loads:
- Uplift Wind Load – This wind load exerts an upward force, so it can affect roofs and other structures positioned horizontally on a building, such as awnings. This is the wind that flows under the structure and pushes upwards.
- Shear Wind Load – This is the horizontal force exerted by the wind against vertical surfaces, including the vertical pitch of a roof, the walls, windows, etc. High shear wind loads can cause a building to tilt.
- Lateral Wind Load – This is another horizontal pressure, but lateral wind load can force a structure to move from its foundations or overturn.