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RESTalk EP32: What is the IAF with Philip Fairey of FSEC

Sep 6, 2019


Feedback (tasting) and adjusting makes for a better recipe. And RESNET is all about feedback.

Such feedback resulted in the development of the Index Adjustment Factor (IAF), also called the Home Size Adjustment Factor in Addendum E-2018. Join us as Philip Fairey, Deputy Director of the Florida Solar Energy Center and Secretary of the RESNET Board of Directors tells us how it all came together.

The IAF stemmed from anecdotal reports that unwarranted HERS® credit was given to larger homes or that smaller homes were penalized. These inequities in rating calculation were believed to be caused by the presence of two factors causing the HERS® Index to fall: larger conditioned floor area and a greater number of stories. Additionally, one factor, a greater number of bedrooms, was observed to be causing the Index to rise.

After extensive research and detailed modeling, the IAF was developed and has helped to significantly reduce the range of variation for all three factors. The IAF is “baked” into the modeling software and does not cause any change to the responsibilities of a Rater or RFI and does not increase the cost of HERS® ratings.

To learn more, including in-depth technical details, see slides from Philip’s presentation at the 2019 RESNET Conference at this link: www.bit.ly/RESNET-IAF   (note: HERS® Raters will be required to use the size adjustment compliant software on homes that are issued a building permit on or after January 1, 2019.)