Windows and Insulation in Boise: ENERGY STAR Criteria Against Idaho's Building Code
ENERGY STAR, Idaho Administrative Code, U.S. Department of Energy. Data covers Rules and published figures as read November 12, 2026.
Summary
Idaho's building code allows a window U-factor as high as 0.32 in the Boise area, while ENERGY STAR requires 0.22 or lower in the same climate. The code calls for R-38 in ceilings; ENERGY STAR recommends R-60 for an uninsulated attic. ENERGY STAR's model puts Boise savings from replacing every window in a typical house at about $202 to $356 a year.
Boise and all of Ada and Canyon counties are in ENERGY STAR's Northern climate zone, where a certified window must have a U-factor of 0.22 or lower under Version 7.0 of the specification, in effect since October 23, 2023. Source [2], [1]
Idaho's residential energy code allows a window U-factor as high as 0.32 in the Boise area, so the ENERGY STAR limit of 0.22 is about 31% lower than the code maximum. Our calculation from [7], [1]
ENERGY STAR's model estimates that replacing every window in a typical Boise house saves about $356 a year when the old windows are single-pane clear glass and about $202 a year when they are double-pane clear glass. Source [3], [5]
Across ENERGY STAR's Northern zone, the modeled average saving is $568 a year (12% of the utility bill) for replacing single-pane windows and $282 (6%) for double-pane clear windows. Source [4]
Idaho enforces the 2018 International Energy Conservation Code for homes with state amendments, and the U.S. Department of Energy rates the amended code as equivalent to the 2009 edition. Source [8], [7]
For the Boise area, Idaho's code calls for R-38 in ceilings, R-20 (or R-13 plus R-5 continuous) in wood-frame walls and R-30 in floors. Source [7]
ENERGY STAR recommends R-60 for an uninsulated attic in Boise's climate zone and R-49 for an attic that already has 3 to 4 inches of insulation, against the R-38 Idaho's code requires for ceilings. Source [6], [7]
Ada and Canyon counties are in climate zone 5B, classed as "Cold," on the U.S. Department of Energy's county climate zone lists. Source [9]
| Component | Idaho code (zone 5) | ENERGY STAR |
|---|---|---|
| Window U-factor (lower is better) | 0.32 maximum | 0.22 maximum (Northern zone certification) |
| Window solar heat gain (SHGC) | No requirement | 0.17 minimum (Northern zone certification) |
| Skylight U-factor | 0.55 maximum | 0.45 maximum |
| Ceiling or attic insulation | R-38 | R-60 uninsulated attic; R-49 with 3 to 4 inches existing |
| Wood-frame wall insulation | R-20, or R-13 plus R-5 continuous | Add R-5 to R-10 insulative sheathing when siding is removed |
| Floor insulation | R-30 | R-30 |
| Basement or crawlspace wall | R-15/19 | R-15 insulative sheathing or R-19 batt |
Code values are from Idaho's amended prescriptive table. ENERGY STAR window values are certification criteria; its insulation values are retrofit recommendations based on the 2021 model code.
| Area | Replacing single-pane clear | Replacing double-pane clear |
|---|---|---|
| Boise, Idaho | $356 a year | $202 a year |
| Northern zone average | $568 a year (12%) | $282 a year (6%) |
Boise figures are rounded from the spreadsheet's $355.64 and $201.76.
These are simulation results, not measurements. ENERGY STAR models one house: 2,376 square feet, two stories, with window area equal to 15% of floor area, and it replaces every window. The Boise figures use Idaho state-average energy prices built into the model ($7.68 per million Btu of gas and 10.58 cents per kilowatt-hour), not current Idaho Power or Intermountain Gas rates.
A house with fewer windows, or one that already has low-e double-pane glass, would save less than the double-pane clear figure. ENERGY STAR states that actual savings will vary.
Idaho amended the insulation and window table when it adopted the 2018 code, so its values are Idaho's own and not the unamended model code's. ENERGY STAR's attic guidance is based on the 2021 model code, which Idaho has not adopted. Both figures are correct; one is the legal minimum and the other is a recommendation.
- ENERGY STAR criteria are from the Version 7.0 specification for residential windows, doors and skylights; the county zone assignment is from ENERGY STAR's climate zone spreadsheet.
- Idaho code values are from the amended prescriptive table in IDAPA 24.39.30, the current Building Code Rules. Code status is from the U.S. Department of Energy's state status page.
- Savings are from ENERGY STAR's city savings spreadsheet (Boise row) and its October 2023 zone summary.
- The 31% comparison is our arithmetic: 0.22 against 0.32.
- Savings are modeled for one typical house and whole-house replacement.
- Local amendments by individual cities were not checked.
- Idaho's building boards state they are not engaged in rulemaking for 2026 to 2027; the code could change after that.
- ENERGY STAR's insulation recommendations use a newer model code than Idaho enforces.
- A percentage saving for the Boise row was not read from the spreadsheet; only zone-level percentages are reported.
Each reference below is cited for a specific claim on this page. Codes, fees and product specifications change — confirm current requirements with the authority having jurisdiction before relying on them for a project decision.
- [1] ENERGY STAR Program Requirements for Residential Windows, Doors and Skylights, Version 7.0 (ENERGY STAR (U.S. EPA))
Cited for: Northern zone window, door and skylight criteria. Accessed November 12, 2026.
- [2] ENERGY STAR climate zones by county (ENERGY STAR (U.S. EPA))
Cited for: Ada and Canyon counties in the Northern zone. Accessed November 12, 2026.
- [3] ENERGY STAR City Savings Estimates Spreadsheet (ENERGY STAR (U.S. EPA))
Cited for: Boise modeled window savings. Accessed November 12, 2026.
- [4] ENERGY STAR Windows Climate Savings (October 2023) (ENERGY STAR (U.S. EPA))
Cited for: Northern zone average savings. Accessed November 12, 2026.
- [5] Methodology for ENERGY STAR Savings Estimates for Windows (ENERGY STAR (U.S. EPA))
Cited for: Model house and baseline windows. Accessed November 12, 2026.
- [6] Recommended Home Insulation R-Values (ENERGY STAR (U.S. EPA))
Cited for: Attic, wall, floor and basement recommendations. Accessed November 12, 2026.
- [7] IDAPA 24.39.30, Rules of Building Safety (Building Code Rules) (Idaho Division of Occupational and Professional Licenses)
Cited for: Idaho prescriptive window and insulation values. Accessed November 12, 2026.
- [8] Building Energy Codes Program: Idaho (U.S. Department of Energy)
Cited for: Code edition in force and DOE equivalence rating. Accessed November 12, 2026.
- [9] Guide to Determining Climate Regions by County (Building America, Volume 7.3) (U.S. Department of Energy)
Cited for: Climate zone 5B for Ada and Canyon counties. Accessed November 12, 2026.
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Iron Crest Remodel. "Windows and Insulation in Boise: ENERGY STAR Criteria Against Idaho's Building Code." Published November 12, 2026; reviewed November 12, 2026. https://ironcrestremodel.com/research/products/boise-window-insulation-standards
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