Over the past 10 years, there has been a shift in minimum required R-values. The 2015 International Energy Conservation Code (IECC) is the driving force behind this movement. More than 20 states have adopted the 2015 IECC, or a portion of its provisions, as their statewide energy code. See the chart below for minimum R-values per climate zone.
Since 2009, the roofing industry has seen an R-10 increase in the majority of the states. The total minimum insulation thickness has increased from 3.5" (R-20) to 5.2" (R-30) in parts of over 40 states. The map below can help you identify climate zones within your state. Climate zones 4 through 8 have experienced an R-10 increase.
Additional resources are provided below to help you determine the applicable energy code and its associated minimum R-value requirements in a given state or local jurisdiction.
1. Minimum Insulation R-value Requirements: Non-Residential, Above Roof Deck
2. The Building Codes Assistance Project
For more information on R-value requirements, please contact Brandon Reynolds at firstname.lastname@example.org