With hurricane and typhoon season upon us, now is a good time to prepare for wind storms. Few other perils can match the wind of a severe tropical storm, such as hurricanes, typhoons and cyclones, in its ability to cause widespread devastation.
During the past 10 years, nine percent of all the damage sustained by AFM clients was related to wind. Approximately 70 percent of all wind losses are attributed to damage during severe tropical storms. By taking preventive measures, clients may avoid being part of future loss statistics. There is no guarantee against wind storm-related damage to property, but it can be minimized with proactive measures, especially when it comes to securing roofing and windows.
Wind forces on a building create an action similar to that of wind passing over an aircraft wing. Changes in the wind's direction as it passes over and around the building result in uplift, or suction, forces. These forces vary dramatically in magnitude on different parts of the building. For example, at the perimeter edge of the roof, the uplift force can be approximately 70 percent higher than on the main (field) part of the roof. In the corners, wind forces can be nearly 160 percent higher. In a case where a single window or door fails, positive pressure can be created within the building envelope to further increase total wind load to the roof. Clearly, this means that if the corners of the roof experience the strongest force, these are the areas that will probably fail first. AFM's loss experience bears this out. It also tells us that if these small corner areas are reinforced with additional fastening, they are less likely to fail.
Meeting code is not enough
Many clients think building to code will protect their property, but building codes may or may not protect and preserve property, as their primary focus is often on public safety. That's why AFM recommends following FM Global Property Loss Prevention Data Sheets. These documents contain guidance that can help reduce costly commercial property loss and business interruption. The product of more than 180 years of loss prevention research and engineering, these data sheets offer our advice about how to mitigate numerous hazards, including windstorms.
One of the costliest impacts of these storms is the damage that results when a building's envelope is torn open and lets wind and rain into the facility. Here are mitigating measures your clients can take if they are in a wind storm-exposed area:
- Screw down the flashing. If you can pull on the flashing and it moves away from the building, it's too loose. This part of the building is subject to the strongest forces and is critical to keeping the covering in place.
- Know your weaknesses. If a roof is suspect, create a contingency plan to ready yourself for a storm. The corners of the roof will likely fail first, so plan to move or cover the stock under these areas.
- Ask your AFM account engineer if the roof will withstand likely wind forces.
- Provide additional fasteners in the corners and perimeter of the roof to meet AFM recommendations.
For more preparation advice, visit AFM's Natural Hazard Toolkit.