Commercial roofs are designed to withstand high winds categorized as wind up to 65mph and some fully adhered flat roof systems are designed to withstand up to 90mph winds, however no roof is designed to withstand the extreme winds from a tornado or micro-burst. Flat & Metal roofs can be severely damaged in these extreme wind events. If your roof was poorly installed (9 out of 10 are installed wrong) even winds that are 40-65mph could damage your roof. With a Smartinspect Roof Survey we will identify any visible wind damage on your roof. In the event your roof is damaged by wind we will recommend that you contact your insurance company and we will assist you in the claims process to make sure that the insurance company gets everything covered.
As the high winds move across your roof the effects of the wind are not uniform. Certain parts of your roof are subjected to much higher wind pressure and damage. The perimeter of the roof is always the most damaged portions of a roof during a high wind event. The center of the roof will have lower stress from wind. When the wind changes directions such as hitting an outside wall, it increases in velocity and wind speed as it goes up and over the wall onto the roof and creates a suction effect as it blows over the edge. This is where the most damage will typically occur.
Depending on the shape of your building and the height of the roof there could be a negative wind pressure or a “Suction” as the wind crosses the roof or there could be a positive wind pressure or a “Pushing” effect.
Wind isn’t typically a problem until it starts to move the roofing membrane. Any loose flashings or membrane or even if your membrane is poorly glued to the walls or even worse not adhered at all then these areas are most likely to be the beginning of the wind damage.
Ballasted roofs such as an EPDM or Tar and Gravel roof are highly susceptible to what we call “Scrubbing” which is where the wind blows the loose gravel across the roof away from the perimeter walls. This can be especially damaging as the ballast is the only thing that holds your roof in place so if the gravel or rock is blown away from the walls your roof is likely to be damaged.
Many times, a building owner or manager will simply glance at the roof after and see that the roof is still intact after a high wind event, but the most damage we see with our Smartinspect Roof Surveys is typically not from the membrane blown off the roof, but debris that been blown across the roof such as glass, tree branches, etc. We have even seen an HVAC unit that wasn’t properly fastened to the curb blow across the roof like a Kansas tumbleweed blowing across a field. The difference is that with each turn it will puncture or cut the roof membrane open creating severe damage to a roof.
Recently we saw an apartment roof that the wind completely lifted the poorly installed fully adhered Built-Up roof and then sat the roof back in its place, so the roof appeared to be intact, but in fact was no longer adhered to the roof substrate and began leaking. It took 2 years and several engineering firms and wind experts to prove to the insurance company what had happened and to get the damaged paid for by the insurance company.