Building codes tend to focus on measures to ensure structural integrity. Since Hurricane Andrew in August, 1992, building codes in hurricane prone regions have been dramatically revised to minimize structural failure during tropical storms. Yet research by FEMA and the Florida Association of Home Builders after the 2004 hurricane season found that wind-induced building failure accounted for a small percentage of the overall storm-related damage. Most of the damage that resulted from the storms of 2004 was due to water infiltration, even in homes built according to current code standards.
Hurricane force winds can drive torrential rains through even the smallest openings in a building envelope. Common points of entry for wind-driven rain include:
• Gaps around water line and electrical conduit penetrations in exterior walls
• Crevices around windows and doors
• Mortar joint cracks in masonry walls
• All forms of roof vents
• Gable end vents
• Ventilated soffits.
It’s important to realize the cumulative effect of such small openings. For example, a continuous crevice only 1/16 inch wide around a 36 inch square window creates an overall opening of 9 square inches. That is the equivalent of having a 3 inch square hole in the wall. And if the windows, doors, soffits or portions of the roof fail, the amount of wind-driven rain entering through these larger openings is immense. This emphasizes the importance of protecting windows and doors from the impacts of wind-borne debris and detailing soffits, vents and roofs in a way that reduces the likelihood of wind-induced failure during storms.
The pressure differentials created by hurricane force winds contribute to the problem of water infiltration. The section on Wind Loads above described how wind striking a vertical wall or roof plane creates positive pressure and wind flowing over and around the walls and roof planes away from the direction of the wind creates negative pressure. These pressure differentials create suction that draws rain water through small openings on the windward side of the home and distributes it throughout interior cavities. As a result, hurricane force winds not only drive water through cracks, they drive the water up into the surrounding spaces. For example, the pressure differentials created by Category 2 force winds can drive water through a small crack and up to 4 inches into the interior space. The pressure differentials created by a minimal Category 5 storm can drive water over 8 inches up into interior spaces.
A major problem with storm-induced water infiltration is that anything that gets wet is likely to stay wet for a long time. Rain soaked insulation in ceilings or cavity walls is difficult to remove and, with the extended power outages that occur after major storms, is unlikely to be dried out by air conditioning systems. Damp, concealed building components such as insulation, drywall and carpeting combine with high ambient air temperatures to support mold growth. Add to this the cost of clothing, furniture, appliances and other personal property destroyed by rain and it is no surprise that water infiltration was found to be the overall most damaging feature of the 2004 hurricanes.
source for above images: FL Division of Emergency Management
To finish Module 1, complete and submit the Final Exam. After you have viewed your results, follow the steps to apply for your Module 1 certification.
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It’s important to realize the cumulative effect of such small openings. For example, a continuous crevice only 1/16 inch wide around a 36 inch square window creates an overall opening of 9 square inches. That is the equivalent of having a 3 inch square hole in the wall. And if the windows, doors, soffits or portions of the roof fail, the amount of wind-driven rain entering through these larger openings is immense. This emphasizes the importance of protecting windows and doors from the impacts of wind-borne debris and detailing soffits, vents and roofs in a way that reduces the likelihood of wind-induced failure during storms. 
