In 1970, Hurricane Celia devastated the Texas coast, leading to the establishment of the Texas Windstorm Insurance Association, or TWIA, an agency of the Texas Department of Insurance. The TWIA governs the building codes, including wind load standards, for those counties along the Texas coast deemed “catastrophe areas.” The Texas Insurance Commissioner may designate any part of the state as a potential catastrophe area if the area frequently suffers severe damage from wind or hail, making private insurance premiums unreasonable to a significant number of property owners.
The 2006 International Building Code and the 2006 International Residential Code contain the requirements adopted to determine a structure’s eligibility for hail and windstorm insurance from the Texas Windstorm Insurance Association. All new construction, additions and repairs since June 1, 2008, should comply with one of these codes.
The TWIA wind load guidelines apply to all residential structures as well as some commercial buildings that are on Texas’ Gulf Coast in the area designated as a potential catastrophe region. The counties covered are Aransas, Brazoria, Calhoun, Cameron, Chambers, Galveston, Harris (east of Highway 146), Jefferson, Kenedy, Kleberg, Matagorda, Nueces, Refugio, San Patricio and Willacy.
In Aransas and Galveston counties, openings with a seaward exposure must be capable of withstanding a three-second wind gust with a wind speed of 130 miles per hour. Inland exposures in those counties must withstand a three-second wind gust moving at 120 miles per hour. Exterior openings in all of Chambers and Calhoun counties must conform to the three second, 120 mile per hour gust, as well as those parts – roughly half – of all other counties in the coastal catastrophe area. Beyond the coastline, the remainders of these counties lie in the Inland II area, where openings must be capable of withstanding three-second wind gusts of 110 miles per hour.
Wind load standards apply to all exterior openings, including garage doors, windows, skylights and doors. In Inland I areas, glass on the bottom 60 feet of the structure must be made or covered with an impact-resistant material. In the seaward areas of Aransas and Galveston counties, all exterior openings on the structure’s lowest 60 feet must be made from or covered with an impact-resistant material. No such requirements exist for structures in the Inland II areas. Wood shutters or other wooden protection panels may be an acceptable substitute for an impact-resistant material. Shutters in Inland I areas must be at least 7/16 of an inch thick, span no more than 8 feet per panel, be precut to fit the opening, and be affixed no higher than a second story. Shutters in the seaward area have the same requirements except that they must be at least 15/32 of an inch thick.
Standards Beyond the Catastrophe Area
As the distance from the coast increases, the wind load standards decrease. In the second coastal tier, consisting of the balance of Harris County and Wharton, Bee, Goliad, Brooks, Live Oak, Fort Bend, Victoria, Jackson, Orange, Hidalgo, Wharton, Liberty, Hardin and Jim Wells counties, the standard remains the same as that for Inland II areas, or a three-second gust traveling at 110 miles per hour. Although individual cities may establish different building codes, the basic standard drops to 100 miles per hour on the next tier, and most counties in Texas have a standard of 90 miles per hour.
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