An uplifting experience
Severe wind from powerful storms consistently causes damage to commercial properties with weaknesses in their roofing systems. The wind will tear the roof system off the structure, allowing rainwater to enter and cause significant damage. It's important to know the best ways to prevent such a loss, before it's too late.
Several years ago an FM Affiliated client in Boca Raton, Fla., USA, installed a new roof on their facility. This roof consisted of a layer of Light Weight Insulating Concrete (LWIC) over the top of the existing structural concrete roof deck. The purpose of LWIC is to provide proper water drainage and an insulating value to keep cooling costs down. This roof system was suggested to the client by their roofing consultant as a cost-effective solution.
However, based on FM Affiliated's loss experiences and results from prior wind uplift tests, we knew roofing systems with LWIC have a low resistance to uplift pressures and likely would not protect the facility against the high winds known to occur in that part of Florida, which can reach as high as 140 miles (225 kilometers) per hour.
When the FM Affiliated engineer relayed this information to the client and the broker, they were in disbelief because the roof was only a few years old and they were told it was appropriately designed for the wind speeds in south Florida. To help the broker and client understand the potential hazard, we recommended performing a roof uplift test.
Put to the test
With an FM Affiliated engineer on-site, uplift testing was conducted using a bell chamber that simulates negative pressures, equivalent to what would be experienced during a windstorm. After two (2) tests on the lower roof area failed, the group decided to move on to the upper roof area, where an additional two (2) tests also failed. At that point the group concluded that no further testing was needed, and it became clear that the roof would not hold up to the pressures known to be caused by local winds.
Working together, the client, broker and FM Affiliated developed a plan to improve the facility by installing an FM Approved mechanically attached single-ply membrane roof that would be anchored through the existing LWIC and into the structural concrete roof deck.
Engineering Expertise
The best way to protect a facility in a windstorm is to maintain the building envelope. During a windstorm, damage to the building's structural frame seldom occurs. Yet, a very small breach in the building envelope can easily lead to destruction of a large area of the interior. With proper knowledge and preparation, extensive wind damage can be prevented through simple, cost-effective and practical solutions—even from severe storms.
FM Global consultant engineers and FM Affiliated account engineers work with clients and their brokers to identify key exposures to their facilities and provide practical solutions they can implement to protect their business. In fact, locations that have eliminated building envelope weaknesses fare more than six times better in windstorms than locations with deficiencies.
Working together
Although the client in Florida was not happy to learn the new roof presented a potential wind exposure, in the end they were able to work with their broker and FM Affiliated to better understand the hazard and how it put their business at risk. This collaboration ultimately led to the development of a plan to improve the facility and help protect the client's business.
For more information on about protecting facilities from damaging wind, check out our Natural Hazard Toolkit.