The first thing that homeowners need to know about roofing and wind speeds is how materials are rated. An example of a company that rates roofing materials based on their ability to withstand wind is Factory Mutual Global. This testing laboratory creates windstorms and tests materials to provide ratings such as I 60 or I 90. Many homeowners falsely believe that the number indicates the speed of wind in miles per hour that a material can handle. However, it actually stands for the amount of wind uplift pressure a piece of material can take before it’s torn off the roof. This number indicates pounds per square foot.
It’s also helpful for homeowners to have a basic understanding of why roof damage occurs from the wind. Not all wind causes roof damage; it only occurs when the air pressure below the roof becomes greater than the air pressure above it.
When wind blows over the top of a house, the pressure above the roof decreases. At the same time, the internal air pressure of the roof rises because of air infiltration. A mix of these two simultaneous pressures creates an upward force that can rip shingles off a roof.
The speed of the wind is only one of the many factors that contribute to wind-related roof damage. For example, the overall height of a home and the surrounding terrain play roles in how the house performs in high winds. The ratings that Factory Mutual Global gives to roofing materials take these factors into account. However, because they cannot adjust their ratings for every different house and terrain, the numbers are based on averages.
Wind doesn’t normally rip roofing material from the foundation unless the material is already damaged or there is a strong storm. To improve the chances of the material surviving a brutal windstorm, the homeowner should have professionals do basic maintenance twice a year. This gives the roofers a chance to reattach roofing shingles that are working themselves loose because of the natural elements they deal with every day.
Think you need repair or want a professional opinion about your roof’s health? Call us at 800-681-4169 or on our CONTACT PAGE to request an appointment from one of our trained professional inspectors.