January 21, 2021

How to Stay Compliant with Idaho Updated Residential Energy Codes for 2021


As detailed in past BetterBuiltNW newsletters, several states in the Northwest have energy code updates planned for 2021. Idaho is set to begin adoption of the 2018 International Energy Conservation Code (IECC) with Idaho amendments on homes permitted on or after January 1, 2021.

In Idaho, there are three compliance options for meeting the energy code.

  1. The prescriptive option includes 2018 IECC sections R401-R404. The sections contain mandatory provisions, do not allow tradeoffs, and do not require software tools for compliance.
  2. An alternative is the Total UA Alternative, found in section R402.1.4. This option still has mandatory provisions but allows for U-factors and assembly areas (walls, floors, ceilings, window areas) to be used when determining tradeoffs. Under this option, anyone performing the UA Alternative may use the common software tool REScheck or other approved methods/software.
  3. The third option is the performance option as described in section R405. This option still has mandatory provisions but allows for one to perform a simulated energy performance analysis that compares designed annual energy costs to a reference home or Energy Rating Index for compliance.

The amendments for Idaho are centered around a few key options that impact both mandatory provisions and performance options. Under the prescriptive amendments, the hot water pipe insulation requirements were amended to specify insulation for hot water pipes outside of conditioned space, those buried or under slabs, and those serving more than one dwelling unit, as well as to address hot water circulatory systems. The window U-value was amended to U-0.32. Lighting was amended to require 75% high efficacy, as well as climate zone specific amendments to attics in climate zone 5 and wall options in climate zone 5.

Perhaps the biggest amendment is adopting building envelope tightness testing. The Idaho amendment outlines changing the leakage target to five air changes per hour (5 ACH) and the requirement for testing to be performed on 20% of homes, instead of 100% of homes. This last amendment also includes a delayed implementation, to allow for industry training, going live as a code requirement in July 2021. For the performance option, the Energy Rating Index was amended to a score of 68 for the entire state.

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