Efficient Windows

New provisions in the IRC and IECC are making houses greener

Posted on Dec 4 by Lynn Underwood, GBA Advisor

9 Steps to A Greener Code

New homes built using the 2009 International Residential Code (IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.) or International Energy Conservation Code (IECC International Energy Conservation Code.) will be more energy efficient than ever. As a consequence, a builder’s world may become a bit more complex and, in some cases, a bit more expensive.

STEP 6: EFFICIENT WINDOWS

Code: N1102.1 In certain warm climates, the thermal performance of windows has been increased.
What it means to you: Heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. or heat loss from windows causes a significant loss of energy. Windows are rated by U-value, which is the inverse of R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. . The lower the number, the more efficient the window is at blocking heat flow. In climate zones 1 to 4, which are generally hotter in the summer, U-values have decreased, representing an increase in energy efficiency.

Solar-heat-gain coefficients (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.) measure how well a window blocks heat from sunlight. these standards also have changed. SHGC is expressed by a number between 0 and 1. The smaller the number, the less solar heat is transmitted into a home. In hotter climates (1 to 4), the SHGC requirement has been reduced considerably, which reduces the stress on cooling equipment and overall home operating costs.

The 2009 building codes reflect practices that not only increase energy efficiency—air-sealing measures and increased insulation, for example—but also address sustainable building practices, such as moisture control.