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Idaho Residential Energy Efficiency - New Report Provides Important Insights

Posted By Johanna M. Bell, Friday, February 15, 2019
Updated: Sunday, March 10, 2019

Energy codes in Idaho have provided for significant energy efficiency gains within the built environment - benefiting building owners and communities across Idaho.  Energy codes for Idaho's buildings are the only codes that return money to their owners by paying dividends each month.

Benefits to homeowners in particular provide not only a more durable and resilient home, but also a cleaner, quieter, and healthier home!

As the Idaho Building Code Board looks into updating the current Idaho Residential Energy Conservation Code by adopting the 2018 codes for Idaho, we now have some additional resources to inform our discussions and training priorities.  Utilizing Northwest Energy Efficiency Alliance (NEEA) dollars for field work, and U.S. Department of Energy (DOE) dollars for analysis and reporting, an Idaho residential energy code field study was undertaken during calendar year 2018. The purpose of the study was to assess potential statewide compliance with the Idaho Energy Conservation Code (effective from January 1, 2015), so that energy code training and technical assistance can be customized to help contractors and trades construct more energy efficient and cost‐effective new homes for Idaho home buyers.

The final Idaho Residential Energy Code Field Study, and supporting Idaho Memo, outline how new homes in Idaho use less energy than would be expected relative to homes built to the minimum Idaho Energy Conservation Code requirements.

For example, the collected data indicates an average energy use intensity of 34.62 thousand Btu’s are used per square foot whereas, the code would allow 40.51 thousand Btu’s of energy per square foot. This is a whopping 15% difference! If looked at like a mpg standard for cars and the minimum standard was 20 mpg, the Idaho car would be averaging about 24 mpg. As for compliance with current codes, the study showed that new residential buildings have a 97% energy code compliance rate, up from the 90% rate documented in a 2013 study, also funded by NEEA.

All‐in‐all, Idaho residential building professionals and trades are doing great at achieving energy efficiency - including more than is required by the current Idaho Energy Conservation Code.  This suggests that Idaho homeowners can feel assured that they are receiving what they are paying for, plus some!

Looking closer at the report results, there are still some important areas where improvement is needed:

First, the work force needs education on insulation installation. The quality of wall insulation installation (including basement walls) and floor insulation, across the state were at a Grade II level in over 60% of homes. A Grade I level of installation would provide greater home owner comfort and energy savings.

Second, duct leakage in one of Idaho climate zones (i.e., climate zone 5, located in southwest and north central Idaho) is higher than allowed by the Idaho Energy Conservation Code. This makes a big difference in homeowner comfort as ducts deliver the air that heats and cools occupants. If conditioned air is leaking into building cavities like roof and floor assemblies, it’s not doing as thorough a job of making the home comfortable. And, it ends up costing the home owner more for heating and cooling.

Third, many homes did not meet the prescriptive Idaho Energy Conservation Code even as they delivered savings greater than minimum code. For example, not all insulation met 2009 levels, but overall, buildings performed better than code in the models because some code requirements such as the air tightness were surpassed. It should be noted that either a performance (energy modeling) or U‐factor (REScheck) analysis are acceptable compliance approaches and both are deemed as alternatives to the prescriptive methodology. 

Fourth, although Idaho homes are beating the current Idaho Energy Conservation Code by 15%, it is important to note that current code uses 2009 IECC values for insulation. Products, insulation standards, and codes have not remained static in the past nine years. The current 2018 IECC has cost‐effective requirements that would increase comfort and efficiency over the current Idaho code.

The full study can be found on the DOE website energycodes.gov; Look under Highlights and Energy Code Field Studies on the front page of the site.

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