Air Freezing Index (IRC vs NOAA)
Hello, we’re in the early planning stages for building our residence in Freeport, Maine this year. It’ll be about 2000 sq ft with detached garage (unheated, with living space above). We hope to build on a Frost Protected Shallow Foundation, utilizing a foam form system such as WarmFörm or similar.
IRC 2015 specifies that our Air Freezing Index is 2500 (Cumberland County, Maine), but using comparable locations (Portland, Lewiston, Augusta) NOAA says we’re in the 1400s (100 yr average here https://www.ncdc.noaa.gov/sites/default/files/attachments/Air-Freezing-Index-Return-Periods-and-Associated-Probabilities.pdf)
Does anyone know why there is such a large discrepancy between NOAA and code? Has anyone worked with their local code enforcement to build to a different AFI than specified in IRC? The discrepancy represents a significant difference in the requirements for skirt insulation width and thickness, and footing depth for both foundations. I’d imagine we’ll end up just building to code, but it does make me curious.
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