Designing Roofing Systems to Withstand Derecho Windstorms

Aug. 2, 2023
While perhaps less widely known than some of the other catastrophic weather events often covered in the news—hurricanes, tornadoes, blizzards, and droughts—a derecho can cause incredible destruction. In August 2020, a derecho ripped through the Midwest. With maximum wind speeds of 140 mph, this storm was the equivalent of an EF3 tornado and a category 4 hurricane. It covered 770 miles in 14 hours and caused over $7.5 billion in damages across the Midwest. 

The storm took its toll on commercial properties and their roof systems. Most existing roofing systems in the path of the derecho were compromised. In some cases, roofing components were found in nearby parking lots and fields. In others, the roofing system was blown off completely, leaving the entire building exposed. 

After analysis of the impacted areas, it was discovered that all 29 roofs utilizing a Carlisle RapidLock system remained fully intact.

The FleeceBACK RapidLock roofing system is a revolutionary method of membrane attachment that provides a fully adhered system without the use of adhesives. The RapidLock systems utilize VELCRO Brand Securable Solutions along with 115-mil and 145-mil FleeceBACK RapidLock EPDM or 115-mil and 135-mil in both FleeceBACK RapidLock TPO and FleeceBACK RapidLock PVC. The resulting mechanical bond achieves performance on par with traditional fully adhered single-ply systems, without the need for stirring adhesives or waiting for flash-off.

This new, adhesive-less solution also offers several other benefits that make it ideal for new construction and re-roofing projects. The RapidLock system is VOC- and odor-free, has no application temperature restrictions, and provides significant labor savings thanks to the simplicity of the system and ease of installation. The new approach provides up to 80% labor savings when compared to the installation of a traditional bonding adhesive and up to 25% labor savings when compared to the installation of a traditional FleeceBACK system. The new system contains 67% fewer seams than modified bitumen. 

The fleece reinforcement adds toughness, durability, and enhanced puncture resistance. The 115-mil membrane delivers 33% greater puncture resistance and 33% greater breaking strength than 60-mil.

Perhaps the greatest proof of the durability of this FleeceBACK RapidLock solution is the fact that the roofing systems with RapidLock EPDM, TPO, and PVC all withstood the consistent and intense conditions generated by the derecho.

Several RapidLock projects in the derecho’s path experienced the storm’s most violent moments, including two schools in Marion, Iowa which withstood 130+ mph winds. These new construction projects were nearly identical in design, each measuring roughly 75,000 sq. ft. Although sections of the metal edging were incomplete when the derecho arrived in Marion, RapidLock’s superior mechanical bond held firm and outperformed other completed roofing systems in the area.