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Resisting wind:

New construction details for high-wind areas are for residential buildings

David Bowman, P.E., Posted 05/01/2009

New construction guidelines have been developed to increase public safety in hurricane-prone areas and other high wind regions. The guidelines, from the International Code Council, Washington, D.C., cover cold-formed steel framing, as well as wood-framed and masonry construction.

The ICC-600 Standard for Residential Construction in High Wind Regions provides wind resistant design and construction details for residential buildings. The standard applies to areas in which wind speeds reach 100 to 150 mph, including the hurricane-prone regions of the East and Gulf Coasts, coastal Alaska, and the special wind region of the Columbia River Gorge in Washington and Oregon.

Prescriptive Designs

ICC-600, approved by the Washington, D.C.- based American National Standards Institute, uses the latest engineering and scientific knowledge to improve the structural integrity and performance of homes. The standard replaces SSTD 10-99, the ICC Standard for Hurricane Resistant Construction, which addressed prescriptive designs for only wood framed and masonry construction. ICC-600 includes prescriptive designs for wind speeds up to 150 mph with three-second gusts and includes provisions for cold-formed steel framing in addition to the masonry and wood framed construction it covered in the previous edition. The new standard also addresses exterior wall coverings and roof assemblies.

Those who work on homes employing cold-formed steel can find the prescriptive details for the foundation, exterior wall coverings, roof assembly and fenestration within ICC-600. The new standard addresses the connections from framing to foundation and from framing to roof.

Building Geometry

ICC-600 is intended to be a prescriptive standard, meaning that details are provided for construction of a building with no engineering design procedure necessary. The standard is limited to a specific building size and geometry. The building geometry limitations vary, depending on the type of construction used. For cold-formed steel-frame construction, some of the limitations include:

• Maximum number of stories: Three
• Maximum building end wall width (wall parallel to roof framing): 40 feet (12 m)
• Maximum building sidewall length: 60 feet (18 m)
• Maximum bearing wall clear height: 10 feet (3 m)
• Allowable roof types: Gable or hip

Another important limitation is that the structure must be an enclosed structure, with the exception that unenclosed porches of limited dimensions inset into the building are allowed.The standard prescribes the uplift connections required for inset porches.

The standard covers many expected alternatives addressed in typical construction. Roof covering materials addressed include asphalt shingles, wood shakes and shingles, slate shingles, concrete and clay tiles, metal roof panels and metal roof shingles. The provisions of this standard require increased numbers of fasteners and special detailing for roof valleys and flashing.

Fenestration requirements call for impact resistant assemblies in windborne debris regions, which are defined as regions within 1 mile (1.6 km) of the coastal mean high water line, where the basic wind speed is 110 mph or greater, and all regions where the basic wind speed is 120 mph or greater. The impact-resistant requirement applies to windows, unit skylights, sliding glass doors, glass patio doors, doors with glazing and garage doors with glazing.

The standard does not deal with flood resistance. Appendix B of the standard provides guidance for flood-resistant foundations for buildings with wood or light steel-framed walls. A building of wood or light steel-framed walls, not more than two stories high, that complies with ICC-600 may be supported with an Appendix B fl ood-resistant foundation.

Reference Documents

A committee of building safety, government, insurance, manufacturing and industry association officials developed the standard, choosing not to reinvent prescriptive details already available in other standards created by technical experts. As a result, ICC-600 references construction manuals for framing details for both wood-frame construction and cold-formed steel framing.

For wood-framed construction, the referenced document is ANSI/AF&PA Wood Frame Construction Manual, 2001 Edition, written by the American Forest and Paper Association, Washington, D.C. For cold-formed steel construction, the referenced document is ANSI/ AISI/S230 Standard for Cold-Formed Steel Framing-Prescriptive Method for One- and Two-Family Dwellings, written by the American Iron and Steel Institute, Washington, D.C.

The Details

The Standard for Residential Construction in High Wind Regions became available in September 2008 for communities to adopt and is a referenced standard in the 2009 International Residential Code and 2009 International Building Code.

In related news, the ICC subsidiary, International Accreditation Service, has new accreditation criteria for Inspection Programs for Manufacturers of Metal Building Systems, AC472. This comprehensive accreditation program for the inspection of metal buildings is based on the requirements of Chapter 17 of the IBC and provides code officials with a means to approve the inspection programs of manufacturers involved in the fabrication of metal building systems.

To purchase ICC-600, Standard for Residential Construction in High Wind Regions, visit the International Code Council Web site at www.iccsafe.org or call (800) 786-4452. To learn more about IAS Inspection Programs for Manufacturers of Metal Building Systems, visit www.iasonline.org or call (866) 427-4422, ext. 3309.

David Bowman, P.E., is manager of codes at the International Code Council, Washington, D.C. The ICC, a membership association dedicated to building safety and fire prevention, develops the codes used to construct residential and commercial buildings, including homes and schools.

www.iasonline.org; www.iccsafe.org

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