Disaster Survival Hurricane Survival WIND EFFECTS ON BUILDINGS
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| WIND EFFECTS ON BUILDINGS |
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| Friday, 27 August 2004 | |
 Recent major hurricanes in
Florida and along the Eastern Seaboard have taught many lessons on construction
techniques to Emergency Management Agencies, Building officials and Insurers.
After Hurricane Andrew, building codes and their enforcement were strengthened
throughout south Florida to take advantage of these "lessons
learned".The major changes were to dramatically improve the survivability of the structures by ensuring the integrity of the building’s roof and its support system including anchoring to the walls and through to the foundation and protection of the openings in the structure. Windows, doors and garage doors breaches from wind and debris are the common precursors to major damage. The physics of wind are force and mass. Once the envelope of a structure is breached, whether from being blown in or from being broken by flying objects, wind penetrates the structure. Its force will continue with its mass enlarging until it finds a way out, either through collapsing walls, breaking out other windows or lifting the roof. Often times, it will exit in a combination of ways. Roofing systems and their design type create unique problems. Our desire to build homes that are pleasing to the eye is a natural part of our culture and is representative of our chosen life-styles. Not many families would choose to live on a street of bunkers if given the choice. Our life-style choices therefore lead us to homes with roofs that are ill designed and not built for hurricane force winds. Gable ends present a direct vertical surface to the full force of the wind, extended eves create lifting areas for the wind, and roofs without adequate pitch, generally 4x12, create lifting foils that simulate the wing surfaces of an airplane. As winds increase across gently sloping roofs, areas of negative or reduced pressure form, creating lift. Building codes have been revised and inspections have become more rigorous for homes built after 1994. Major strides have been taken to tie the foundation, walls and trusses together to reduce susceptibility to lift. At the same time, the roof sheathing requirements and nailing patterns have been defined to help keep the roofing materials on the house. In 1998, Martin County began requiring for new construction, roof shingles that have been tested to withstand 110 MPH winds. Residential and commercial window units use glass that has been load tested to 110 MPH. However, the testing does not reflect the cyclical nature of hurricane winds and the glass is not required to be impact resistant to stop flying debris. ASSESSMENT AND MITIGATIVE MEASURES FOR THE HOMEOWNER Structural evaluation of your home should be made by an experienced inspector from the construction field who belongs to associations such as the American Society of Home Inspectors or the Florida Association of Building Inspectors, Architects and Engineers. Check the Better Business Bureau for any complaints against him. The cost for this service begins at $200. Anyone considering buying an existing home should have a professional inspection in addition to checking out the builder’s previous projects.
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