Your siding installation and the new insulation code requirements

Your siding installation and the new insulation code requirements

How much do you know about R-value and the effect it can have on your household budget? Probably more than you did just several years ago as the term now figures prominently in just about every discussion about improving a home's energy efficiency. The government's Energy Star website defines R-value as "a measure of insulation's ability to resist heat traveling through it" and provides recommendations for the R-values to use in your home's exterior walls.

The values are based on climate zones, with higher R-values suggested for homes in cold regions where heat loss can have a profound impact on energy costs. However, recent changes to the International Energy Conservation Code may have taken "suggested" out of the equation and could affect the installation of your exterior siding.

The IECC and your exterior siding

The IECC is a building code designed to promote green building practices for commercial and residential construction. According to the International Code Council, the IECC is now in use in 46 states, New York City, and the District of Columbia. When plans are approved or inspections made, the energy code is normally used in conjunction with more traditional building codes such as the International Residential Code.

Why might this be important to someone planning an exterior siding installation for their home? The 2012 IECC code has been updated to require increased R-values for the exterior wall assemblies in new homes for certain climate zones. The new code calls for these values in the exterior walls:

  • Zones 6, 7, and 8 with 6-inch, above-grade exterior walls must have R-20 + R-5 insulation values.
  • Zones 6, 7, and 8 with 4-inch, above-grade exterior walls must have R-13 + R-10 insulation values.
  • Zones 3 and 4 must have a minimum R-value of 20 for their above-grade exterior walls.

In the list above the IECC's geographic climate zones correspond to those used by Energy Star; the first R-value figure for climate zones 6, 7, and 8 is for the insulation in the wall cavity -- values that are fairly common for the indicated wall thicknesses. It's the second R-value, however, which might change your siding installation plans. It must be made up by the exterior siding or insulation board installed prior to your siding application. If you have 4-inch exterior walls, you might need to combine insulation board and insulated siding or several layers of insulation board and standard siding to reach the required R-10.

Keep in mind that the IECC code changes are for new homes only and for those in certain climate zones. However, if you're planning a siding installation soon and hope to put your home on the market one day, meeting these new guidelines is something you should consider.

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