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Code Green

Efficient Windows

New provisions in the IRC and IECC are making houses greener

9 Steps to A Greener Code

New homes built using the 2009 International Residential Code (IRC) or International Energy Conservation Code (IECC) 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.


Code: N1102.1 In certain warm climates, the thermal performance of windows has been increased.

What it means to you: Heat gain or heat loss from windows causes a significant loss of energy. Windows are rated by U-value, which is the inverse of R-value. 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 (SHGC) 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.

Other segments of this series:

Part 1: Air Sealing

Part 2: Insulation

Part 3: Lighting

Part 4: Programmable Thermostats

Part 5: Insulating Mass Walls

Part 6: Efficient Windows

Part 7: Insulating Mechanical Pipes

Part 8: Exceeding the Energy Code

Part 9: Vapor Retarders

One Comment

  1. Interested Onlooker | | #1

    Climate Zones
    Which Climate Zones are generally not hotter in the summer?

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