In 1997, the International Code Council adopted the 0.40 maximum SHGC requirement during its public hearings (the International Energy Conservation Code ("IECC") committee adopted the requirement unanimously for the IECC). Following this lead, the 2000 International Residential Code ("IRC") also incorporated the requirement. The 0.40 requirement has since been reviewed and adopted in a number of other states. Moreover, the United States Department of Energy has determined that the new SHGC requirement is a major improvement to the model energy code (the IECC is the most recent national model energy efficiency code) and promises substantial benefits in cooling climates like Texas (DOE completed its statutorily required review of the IECC in early January 2001). By adopting the IECC and IRC, Texas adopted the SHGC requirement in 2001.
Through Senate Bill 5 and Senate Bill 365, the Texas Legislature adopted and Governor Perry signed legislation to implement the International Residential Code (IRC) energy chapter as the statewide residential building energy code. The IRC requires that the area-weighted average SHGC of all fenestration installed in climates up to 3,500 HDD be below 0.40. The IRC also incorporates the entire International Energy Conservation Code (IECC) as an alternative energy code for homes with glazing areas of 15% and below. However, the IRC requirements can only be used for glazing areas up to 15%. For homes with glazing areas over 15%, builders may only use the IECC.