So far we have talked about roof coverings, but serious failures of roofs often have little to do with what is on top, but rather how all of it is put together. Modern codes in severe storm areas require the use of tie-downs and straps or brackets that hold the rafters to the walls and the walls to the foundations. These codes are much like seismic codes for earthquake prone areas. When storms are severe, hurricane force winds can reduce the pressure above a roof, lifting the roof. This is called the Bernoulli effect and has turned many homes into open-air structures. If your home is old, the rafters may be simply toe-nailed to the wall’s top plates. This simple building method does not provide much resistance to uplift that keeps a roof on during severe conditions.
Most catastrophic failures in intense storms are due to some variation of losing the roof sheathing, with or without the rafters attached. The gable ends of homes are especially vulnerable. Once this layer is gone, water from wind driven rain can completely destroy the homes interior. Often the loss of the ceiling joists or trusses will cause a cascade failure of the walls as well. Another problem that occurs with the loss of the roofs sheathing is that it allows the wind to get a better grip on the home and can cause walls and other areas of roofing to “blow out.” If you are re-roofing, it is a good ideal to add additional fasteners to the decking prior to installing the roof covering. Tie straps and additional structural elements can often be added in attic spaces as well. While these measures can improve the home’s strength, and reduce potential storm damage, they may fall short of current local building codes.
While severe storms may be exciting to watch on the Weather Channel, living though them or rebuilding after one is a completely different matter. Proper maintenance, inspections, and adherence to current building codes and standards will increase the chance that your home is not damaged by a storm.