Small Wind Energy Systems Building Code Compliance Information
Towers are unlike any other building structure. They come in a variety of different types including guyed cables, cantilevered tubes, monopoles and lattice structures, all of which interact differently with wind forces. Turbines on top of these towers are also unique in that they attempt to enhance the effect of the wind and then mitigate its effect after a certain threshold. This complicates modeling scenarios that are used in constructing structural standards and ultimately makes the application of a generic building code on a wind turbine challenging.
Despite this, there are three building code standards which are specifically focused on wind forces and towers. These codes are provided below and they should be consulted in the issuance of building permits for small wind energy systems.
IBC Section 1609: The 2006 International Building Code Section 1609 pertains to wind loads relevant to roofs, walls, windows, doors, etc… The IBC draws much of these calculations from another code, American Society of Civil Engineer (ASCE) 7. Also notable is the list of structures that are exempt to the ASCE coverage. Exemption 4 of 1609.1.1 specifically lists antenna-supporting structures, which include towers.
ANSI/TIA-222-2005: Under the exemption given to towers in section 1609, the structural standards are referred to the American National Standard Institute (ANSI)/Telecommunications Industry Association (TIA) rule 222-G, updated in 2005. This code is the governing standard for tower construction and it is the only code to have been vetted through years of testing. Much of the tower industry is still using the TIA/EIA 222-F code, though from a technical standpoint it became obsolete as of January 2006. The 222-G is more rigorous, conservative and comprehensive.
ACI-318-2005: The American Concrete Institute (ACI) has analyzed tower loads on concrete foundation and have developed standards to handle these loads. ACI-318-2005 is the latest code that governs this topic.
Because of the inherent difficulty in apply building codes onto towers used for wind turbines, turbine manufacturers have had to rely on actual test data to provide real-world information on turbine forces. These studies conducted at the National Renewable Energy Laboratory, among other institutions, are significant towards ensuring the safety of the public as more small wind energy systems are installed. This stresses the importance of small wind energy ordinances having a provision regulating the permissible types of turbines. Lists detailing the small wind turbines that have been approved are available from the California Energy Commission or the New York Energy and Research Development Authority.
For more information please contact:
American Wind Energy Association
1501 M St. NW, 10th Floor
Washington, D.C. 20005
Ph: (202) 383-2546