Historically, the Midwest has been hit by some of the most destructive tornadoes in the United States. For example, the giant “Tri-State” tornado of 1925 destroyed large swathes of Missouri, Illinois, and Indiana. More recently, a huge tornado hit Joplin, Missouri, causing $2.8 billion in damage. As a result, a new Joplin, Missouri roofing code was proposed in 2011 that aims to protect more houses in the event of a similarly strong tornado—to keep the houses intact, and their occupants safe.
This updated code contains new specifications for keeping roofs together, including the phasing out of nails in favor of hurricane ties, which are pieces of galvanized or stainless steel that provide a load transfer path from a building’s roof down to its foundation, protecting it from the impact of strong winds. Most Missouri roof replacement contractors use hurricane ties on the trusses, but the new Missouri roofing code proposes that the ties should also be able to connect the roof to the walls of the house itself.
Most of the damage coming from a tornado can actually be attributed to air pressure coming from building interiors: outward pressure against the side walls, upward pressure against the roof, and inward pressure on the side facing the twister. The roof is often the first to come off, and without anything left to provide lateral stability, the walls collapse soon after, giving the impression that the building is exploding.
Hurricane clips provide protection from the upward pressure that comes with a tornado. They are installed on the top plate and connected to rafters and trusses, and tremendously improve the stability of the connection as compared to just connecting the two structures with nails. Hurricane clips are cheap ($550 for a two-story house measuring 2,500 square feet) and easy to install—particularly if one has a pneumatic drill—and can provide protection against winds as fast as 110 miles per hour. However, it is best to ask a qualified Missouri roof replacement contractor to perform the installation as they are more qualified to calculate the load that will be supported by the clips.
Roofing shingles themselves are susceptible to damage caused by projectiles. While asphalt shingles provide excellent protection from rain and has enough weight to keep them from being blown away, it is particularly vulnerable to tornadoes because of its brittle characteristic. There are products on the market that combine the malleability of cloth with the toughness of concrete. These “concrete curtains,” as they are called, can be draped over most surfaces, providing protection from projectiles flying at over 600 miles per hour.
With strict adherence to Missouri roofing codes and construction industry best practices, tragedies like the 2011 Joplin tornado will soon be a thing of the past for buildings in the “Tornado Belt.”