Colorado's Residential Energy Code, City by City: What REScheck and Manual J Actually Require

1. What the Code Is and Who Enforces It

Colorado doesn't have a "Colorado Energy Code" the way Florida has the Florida Building Code or Washington has the WSEC. The U.S. Department of Energy's own state profile for Colorado lists Current State Code (both Commercial and Residential) as simply "Home Rule" - with "Can use COM/REScheck: Yes" as the general answer, but no single statewide edition, effective date, or adoption date listed at all.¹ That's a structurally different starting point than most of the states covered elsewhere on this site.

What "home rule" means here

In Colorado, cities and counties adopt and enforce their own building and energy codes independently. There is no state agency that reviews residential plans or issues permits directly - that happens entirely at the local level, through each city's building department or, for unincorporated county land, the county's building department (or, in the Colorado Springs area, a regional authority covering several jurisdictions at once - more on that below).

The state floor: HB19-1260 and HB22-1362

Home rule doesn't mean "anything goes." Colorado has passed two significant state laws that constrain what local jurisdictions can adopt when they update their codes:

• HB19-1260 (2019) amended C.R.S. 30-28-211 to require that any local jurisdiction adopting or updating a building code must adopt, at minimum, one of the three most recent versions of the IECC (or a successor edition), rather than being able to adopt an old or arbitrary edition. The bill passed the House 41-2 and the Senate 22-2, and was signed into law effective August 2, 2019.²
• HB22-1362 (2022) went further. It created the Colorado Energy Code Board (a joint body appointed by the Colorado Energy Office and the Department of Local Affairs) and required that board to develop two model codes: a Model Electric Ready and Solar Ready Code and a Model Low Energy and Carbon Code. The act specifies that on or after July 1, 2023, and before July 1, 2026, any municipality or county that updates a building code must adopt and enforce an energy code achieving equivalent or better performance than the 2021 IECC plus the Model Electric Ready and Solar Ready Code. On or after July 1, 2026, that same trigger requires adoption of the Model Low Energy and Carbon Code (or an equivalent/more stringent code) instead.³

The Colorado Energy Office's own Building Energy Codes page confirms this timeline directly: "State law requires local jurisdictions to adopt and enforce the Colorado Model Low Energy and Carbon Code upon updating any other building code" as of July 1, 2026, and that from July 1, 2023 to June 30, 2026 the requirement was the 2021 or 2024 IECC plus the Model Electric Ready and Solar Ready Code.⁴ The Model Low Energy and Carbon Code itself is based on a modified 2024 IECC, and was published September 2, 2025.⁴

What actually triggers the requirement

The state's own Energy Codes FAQ page is explicit that the trigger is updating any building code - not just the energy code. State law defines "building code" broadly: the IBC, IRC, IECC, IMC, IFC, IPC, and NEC all count. Adopting or updating any of those triggers the requirement to adopt the current state minimum energy code (except updates to the Colorado Wildfire Resiliency Code, which is exempt from the trigger).³ That's why you'll see jurisdictions that updated their building code in, say, 2022 or 2023 sitting on the 2021 IECC today even though the 2024 IECC exists - they haven't touched their building code since, so the trigger hasn't fired again.

Who enforces it

Enforcement is entirely local - your city building department, your county building department, or (for the Colorado Springs metro) the Pikes Peak Regional Building Department, which serves Colorado Springs, unincorporated El Paso County, Fountain, Manitou Springs, Monument, Green Mountain Falls, Palmer Lake, and Woodland Park as a single regional plan-review and inspection authority. There is no statewide plan-review desk for residential energy code the way some single-code states run one.

Climate zones

Colorado spans four IECC climate zones: 4B, 5B, 6B, and 7.⁵ Pulled directly from the county-by-county climate zone table published in the 2024 IECC's own sample chapter text:

• Zone 4B (mixed-dry) covers the far southeastern plains - Baca, Bent, Las Animas, Otero, and Prowers counties.
• Zone 5B (cool-dry) covers the Front Range corridor and most of the Eastern Plains, including Denver, Boulder, Larimer (Fort Collins), El Paso (Colorado Springs), Adams, Arapahoe, Douglas, Jefferson, and Weld counties - the population center of the state.
• Zone 6B (cold-dry) covers mid-elevation mountain valleys and western-slope counties, including Alamosa, Eagle, Chaffee, Archuleta, and San Miguel counties.
• Zone 7 (very cold) covers the state's highest-elevation mountain counties - Grand, Gunnison, Summit, Park, Clear Creek, Lake, Pitkin, Routt, and Jackson counties among them.

Zone 5B, where most of Colorado's population lives, sits at the boundary between "cool" and genuinely cold design conditions. Zone 7 counties, mostly high-elevation mountain resort communities, are held to the strictest prescriptive requirements in the IECC's residential table. If your project sits near a county line or at unusual elevation for its county, confirm the exact zone assignment with your local building department.

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2. What Actually Changed / Where Jurisdictions Differ

Because Colorado has no statewide default, there's no baseline table to fall back on the way there is in a single-code state - what applies to your project is entirely a function of which jurisdiction is issuing the permit and when that jurisdiction last updated its building code. Verified directly against each jurisdiction's own published adopted-codes page:

Jurisdiction	Currently adopted energy code	Effective date	Source
Denver (City and County)	2021 IECC with Denver amendments (rest of the 2025 Denver Building & Fire Code uses the 2024 I-Codes, but the energy code specifically stayed on 2021 IECC)	December 31, 2025 (2025 code cycle; energy code section adopted June 13, 2025)	City and County of Denver, "Building and Fire Codes" / "Denver Residential Energy Code"6
Pikes Peak Regional Building Department (Colorado Springs, unincorporated El Paso County, Fountain, Manitou Springs, Monument, Green Mountain Falls, Palmer Lake, Woodland Park)	2021 IECC (part of the 2023 Pikes Peak Regional Building Code package)	Current, per PPRBD's own "Current Adopted Code" listing	Pikes Peak Regional Building Department, pprbd.org homepage / Current Adopted Code7
Boulder County (unincorporated)	2021 IECC (including Appendixes CB, CD, RB, RD), part of the 2021 International Codes package	July 1, 2026	Boulder County, "Building Code Amendments"8
Longmont	2024 IECC (part of the 2024 International Codes, plus the Metro Cohort Model Code and Colorado Wildfire Resiliency Code)	July 1, 2026	City of Longmont, "Building Codes"9
Fort Collins	2024 IECC with local amendments, including a mandatory Path to Zero Carbon (Appendix RZ)	April 1, 2026 (adopted at second reading December 16, 2025)	City of Fort Collins, "2024 IECC Final Amendments" ordinance / code chronology10
Monument (via PPRBD's secondary-code process)	2021 IECC plus the Colorado Model Electric Ready and Solar Ready Code, effective as a secondary code layered on the Pikes Peak Regional Building Code	June 30, 2026	Town of Monument, "PPRBD Adopts Energy Codes, Effective 6/30/2026"11

The headline finding: even the six jurisdictions checked for this page span three different code postures. Denver and PPRBD (covering Colorado Springs and its surrounding towns) are both currently on the 2021 IECC. Longmont and Fort Collins have both already moved to the 2024 IECC. And Boulder County, despite adopting the "2021 I-Codes" package, doesn't have that package take effect until July 1, 2026 - meaning a Boulder County permit application today may still be reviewed under the prior 2015-based amendments, depending on the exact application date. This is exactly the kind of one-line-different-per-county situation a generic "Colorado requires X" answer would miss.

The state's Model Electric Ready / Solar Ready Code and Model Low Energy and Carbon Code are not automatically your jurisdiction's code

It's easy to conflate "the state published a Model Low Energy and Carbon Code" with "every Colorado jurisdiction now enforces it." That's not how the trigger works. A jurisdiction that hasn't updated its building code since before the trigger date can still be enforcing an older edition entirely lawfully - the requirement only fires the next time that jurisdiction updates its own building code. Boulder County's 2021 I-Codes package, for example, doesn't take effect until July 1, 2026, even though the state's own July 1, 2026 trigger has already shifted the state-minimum standard to the Model Low Energy and Carbon Code by that same date - meaning Boulder County's newly-effective code needed to be evaluated against that state minimum at adoption. Every jurisdiction's actual enforced edition has to be checked individually; the state minimum defines a floor, not a universal answer.

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3. Your Ways to Comply

Whichever IECC edition your jurisdiction enforces - 2021 or 2024 being the two currently in play among the jurisdictions checked for this page - the same general compliance paths carry forward, consistent with how the IECC's residential chapter has been structured across recent editions:

Path	Typical code section	What it is	Best fit
Prescriptive	R402.1.1/R402.1.2	Meet every line item in the R-value/U-factor table for your climate zone, exactly as published.	Simple plans, standard framing, no unusual glazing, tight budget and timeline.
UA / total-building-envelope trade-off (REScheck)	R402.1.5	Total heat loss (UA) of the actual envelope must be at or below the UA of a prescriptive-minimum reference home. Weak components can be offset by strong ones elsewhere.	2x4 walls, large glazing packages, or an assembly that can't hit every prescriptive number individually but performs well overall.
Simulated performance / Energy Rating Index (ERI/HERS)	R405 / R406	A full energy model or HERS rating compares the proposed design's performance against a standard reference design or scores it on the 0-100 ERI scale.	Custom homes, non-standard HVAC or renewable strategies, or projects already doing a HERS rating for a rebate, tax credit, or green certification.

Which path fits which project:

• Simple, code-minimum spec homes with standard framing - the prescriptive path is fastest through plan review and the cheapest to document.
• 2x4 walls, large window packages, or one weak component - the UA trade-off (REScheck) is usually the cheapest fix, where your jurisdiction's adopted edition is one REScheck supports and the jurisdiction accepts it.
• Custom homes or designs the prescriptive/UA path can't cleanly capture - simulated performance costs more and takes longer, but it's the only path flexible enough for genuinely non-standard designs.
• Already paying for a HERS rating for a utility rebate, ENERGY STAR, or a tax credit - use the ERI path and let that rating do double duty as code compliance.

Where REScheck fits in Colorado specifically. DOE's REScheck currently supports the 2009 through 2024 IECC editions, plus a dedicated "Denver (2019)" state-specific edition, per DOE's own REScheck program page.¹² That covers the 2021 IECC enforced by Denver and PPRBD and the 2024 IECC enforced by Longmont and Fort Collins - but "supported by the software" and "accepted by your specific plan reviewer with your specific local amendments" are two different questions. Because Colorado is home rule, the safest approach is telling us your city or county before we run anything, so we select the correct edition and check whether the jurisdiction's own amendments change how the report needs to be built.

What about Manual J? Every jurisdiction checked for this page enforces an IRC edition (2021 for Denver, PPRBD, and Boulder County; 2024 for Longmont and Fort Collins) that carries Section M1401.3, requiring HVAC equipment to be sized per ACCA Manual S based on loads calculated per ACCA Manual J. That's not layered on by any one city - it's baked into the residential code itself, independent of which IECC edition governs your envelope compliance path. Longmont goes further than most: its own ADU Submittal Checklist lists "Manual J, Manual D, Manual S" as a required document under "Energy Code Certification," with a note that Manual D isn't required if there's no ductwork (e.g., a mini-split system), and that Manual J and S are required specifically when using the prescriptive path (or equipment-sizing calcs must be shown otherwise).¹³

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4. Colorado-Specific Wrinkles

"Colorado code" isn't one thing - confirm the jurisdiction, not the state. With no statewide default and dozens of independent home-rule cities and counties, the single biggest risk on a Colorado project is assuming a code edition based on a neighboring city or a prior job. A builder working Denver and Longmont jobs back to back is working under two different IECC editions (2021 vs. 2024) with two different sets of local amendments, even though both cities sit in the same climate zone.

The state minimum is a moving target by design. Because HB22-1362's trigger shifted from the 2021 IECC + Model Electric Ready and Solar Ready Code (2023-2026) to the Model Low Energy and Carbon Code (2026 forward), a jurisdiction's code edition today doesn't tell you what it will be after the next building-code update. Fort Collins and Longmont have already jumped straight to the 2024 IECC and beyond; other jurisdictions on this page are still on the 2021 IECC because they haven't triggered another update yet. Don't assume a jurisdiction "will obviously update to match the state minimum" on any particular date - the trigger only fires when that specific jurisdiction updates its own building code, and some jurisdictions go years between updates.

Regional building departments cover more than one city. The Pikes Peak Regional Building Department is a single plan-review and inspection authority for Colorado Springs, unincorporated El Paso County, Fountain, Manitou Springs, Monument, Green Mountain Falls, Palmer Lake, and Woodland Park.⁷ That means a project in Manitou Springs and a project in unincorporated El Paso County are reviewed by the same department under the same adopted code - useful to know if you're used to thinking about Colorado in terms of incorporated city limits only.

Elevation and design temperature matter to your Manual J, not just your envelope. Colorado's Zone 6B and Zone 7 mountain jurisdictions carry genuinely cold winter design temperatures, and several jurisdictions - Fort Collins among them - publish their own local climatic/geographic design criteria tables (heating and cooling design temperatures, ground snow load, wind speed) that feed directly into a Manual J calculation, separate from the IECC's climate-zone insulation table.¹⁰ High-altitude HVAC equipment sizing is also a real consideration: ACCA's Manual S accounts for the reduced air density at elevation when derating and selecting equipment capacity, which is why the design temperature and elevation inputs on your specific site matter more in mountain-zone Colorado projects than in most other states covered on this site. Confirm your jurisdiction's specific design-temperature table before finalizing equipment selection.

ADUs are a live, changing area of Colorado law. House Bill 24-1152 (2024), Colorado's statewide ADU law, requires "subject jurisdictions" (generally municipalities over 1,000 population within a metropolitan planning organization area, and certain densely populated county areas) to allow one accessory dwelling unit by-right on lots where single-unit detached housing is allowed, effective June 30, 2025.¹⁴ Denver, Longmont, and other Front Range jurisdictions have already amended their own zoning and building-permit processes in response. If you're building an ADU in Colorado, expect a jurisdiction-specific submittal checklist - Longmont's, for instance, spells out Manual J/D/S plus a HERS report or REScheck depending on your compliance path, as noted above.

What to ask your local building department before you finalize a compliance strategy:

1. Which IECC and IRC editions does this specific jurisdiction currently enforce for residential permits, and when did that jurisdiction last update its building code (the answer changes the state-minimum trigger that applied)?
2. Is my project inside city limits, or does it fall under county or regional-authority (e.g., Pikes Peak Regional Building Department) jurisdiction instead?
3. Does this jurisdiction require the state's Model Electric Ready and Solar Ready Code or Model Low Energy and Carbon Code in addition to a base IECC edition?
4. Do you require a Manual J load calculation (and Manual D, Manual S) to be submitted with the permit, or only upon request?
5. Which compliance-document format do you accept for the envelope path - a REScheck printout matched to your specific edition, a HERS/ERI certificate, or a jurisdiction-specific worksheet?

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5. Frequently Asked Questions

Does Colorado have one statewide residential energy code? No. DOE lists Colorado's current state code as "Home Rule" for both commercial and residential construction.¹ There is no single mandatory statewide edition - local jurisdictions adopt their own IECC edition and amendments, subject to a state-law floor.

What does Colorado state law actually require of local jurisdictions? HB19-1260 (2019) requires any jurisdiction updating a building code to adopt at least one of the three most recent IECC editions.² HB22-1362 (2022) required jurisdictions updating a building code between July 1, 2023 and June 30, 2026 to adopt the 2021 or 2024 IECC plus the state's Model Electric Ready and Solar Ready Code; starting July 1, 2026, that trigger requires the new Colorado Model Low Energy and Carbon Code instead.³

Will a REScheck report be accepted for a Colorado permit? It depends on your jurisdiction. DOE lists Colorado as "Can use COM/REScheck: Yes" generally, and REScheck supports the 2021 and 2024 IECC editions enforced by Denver, PPRBD, Longmont, and Fort Collins, plus a dedicated "Denver (2019)" state-specific edition.¹² Confirm your specific jurisdiction before assuming a standard report will be accepted.

Is a Manual J load calculation required in Colorado? Every jurisdiction checked for this page enforces an IRC edition that requires equipment sizing per ACCA Manual S based on ACCA Manual J loads (Section M1401.3). Longmont's ADU checklist names Manual J, Manual D, and Manual S explicitly.¹³ We offer Manual J everywhere in Colorado, independent of which IECC edition your jurisdiction has adopted.

Who prepares these reports? Travis Smith, a certified Residential Energy Inspector / Plans Examiner - the same certification your building department's reviewer holds.

My city or county isn't one of the ones covered on this page - what do I do? Colorado has dozens of home-rule cities and counties, each free to adopt its own code on its own timeline, so this page can't cover every jurisdiction by name. Check your building department's adopted-codes page or call the plan review desk. Tell us the city or county when you order a report and we'll confirm the edition before we run anything - not a generic "Colorado" answer.

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6. Get It Right the First Time - Before Plan Review Sends It Back

Need a Manual J load calculation? Colorado is a state where we lead with Manual J. Because there's no single statewide edition to default to, and because IRC M1401.3 ties equipment sizing to a documented Manual J regardless of which IECC edition governs your envelope, a room-by-room Manual J report is the one piece of documentation every jurisdiction on this page treats the same way. A Manual J report is $249 for homes up to 3,000 sq ft.

Need a REScheck report too? Tell us the city or county where you're pulling the permit and we'll confirm the adopted IECC edition and any local amendments before running the report - Denver, PPRBD, Boulder County, Longmont, and Fort Collins are not all on the same edition, and we don't submit a report against the wrong one. A REScheck report is $149 once we've confirmed your jurisdiction accepts it for your compliance path.

Need both? The combined Manual J + REScheck package is $349 - one submission covering the equipment-sizing requirement under the residential code and the envelope/compliance requirement under whichever IECC edition your jurisdiction enforces.

Every report comes with the same guarantee: accepted by your building department, or we revise it free until it clears.

Building an ADU? Colorado's HB24-1152 has made ADUs a fast-growing project type statewide, and jurisdictions like Longmont require Manual J, Manual D, and Manual S on the submittal checklist itself. See our Manual J for ADU guide for what that calculation needs to cover.

Contact us with your plans and the city or county where you're pulling the permit, and we'll confirm the adopted code edition and tell you plainly which compliance path fits your project.

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Verification Appendix

Every jurisdiction-specific claim on this page was checked directly against that jurisdiction's own published code-adoption page, the state's own bill text and Colorado Energy Office pages, or a jurisdiction's own permit-submittal checklist during this research pass - not a national aggregator or a secondary blog summary, except where explicitly noted below.

1. Colorado = "Home Rule," no single statewide residential code; DOE "Can use COM/REScheck" = Yes. VERIFIED. energycodes.gov/status/states/colorado's own State Profile table lists Current State Code (Commercial and Residential) = "Home Rule," with no effective/adoption date given, and "Can use COM/REScheck" = Yes for both.¹

2. HB19-1260 (2019): local jurisdictions updating a building code must adopt one of the three most recent IECC editions. VERIFIED. leg.colorado.gov's own HB19-1260 bill page states this directly in its Bill Summary, and the enrolled bill text (leg.colorado.gov/bill_files/63518/download) shows the amended statutory language of C.R.S. 30-28-211(2)(b) and (3), replacing a fixed "2003" edition reference with "one of the three most recent versions of the international energy conservation code." Signed into law, effective August 2, 2019 (Session Laws Chapter 357).²

3. HB22-1362 (2022): Energy Code Board created; 2021 IECC + Model Electric Ready and Solar Ready Code required July 1 2023-June 30 2026; Model Low Energy and Carbon Code required from July 1 2026. VERIFIED. leg.colorado.gov's own HB22-1362 bill page Bill Summary states this timeline directly: "On or after July 1, 2023, and before July 1, 2026, municipalities and counties that update a building code shall adopt and enforce an energy code that achieves equivalent or better energy performance than the 2021 international energy conservation code and the model electric and solar ready code... On or after July 1, 2026, municipalities and counties that update a building code shall adopt and enforce an energy code that achieves equivalent or better energy performance than the model low energy and carbon code." Signed into law June 2, 2022 (Session Laws Chapter 301).³

4. Colorado Energy Office confirms the same trigger timeline and that the Model Low Energy and Carbon Code became the state minimum on July 1, 2026. VERIFIED. energyoffice.colorado.gov/energy-codes-faq states: "Starting July 1, 2026 jurisdictions with building codes must adopt the Colorado Model Low Energy and Carbon Code (MLECC), or an equivalent or more stringent code, when adopting or updating any building code," and confirms the prior 2021/2024 IECC + Model Electric Ready and Solar Ready Code requirement for July 1 2023-June 30 2026. The Colorado Energy Office's press release (Sept. 2, 2025) confirms the Model Low Energy and Carbon Code was published that day and becomes the state's new minimum energy code on July 1, 2026, based on a modified 2024 IECC.⁴

5. Colorado climate zones 4B, 5B, 6B, 7 with county assignments. VERIFIED (primary source). A published 2024 IECC sample chapter (shop.iccsafe.org, Table C301.1) lists every Colorado county with its assigned climate zone; cross-checked against UpCodes' published 2024 IECC and 2021 IECC climate zone tables for Colorado, which list the same county-to-zone assignments.⁵

6. Denver = 2021 IECC (with Denver amendments), while the rest of the 2025 Denver Building & Fire Code moved to 2024 I-Codes. VERIFIED. Denver's own "Building and Fire Codes" page states: "On June 13, 2025, the City and County of Denver adopted the 2025 Denver Building and Fire Codes, which incorporate the 2024 I-codes (except the Energy Code, which incorporates the 2021 IECC)." Denver's "Denver Residential Energy Code" page confirms: "The 2025 Denver Energy Code (DEC) is substantially similar to the 2022 DEC; both use the same base code, IECC-2021."⁶

7. Pikes Peak Regional Building Department (Colorado Springs metro) = 2021 IECC currently adopted; department covers Colorado Springs, unincorporated El Paso County, Fountain, Manitou Springs, Monument, Green Mountain Falls, Palmer Lake, and Woodland Park. VERIFIED (primary source). pprbd.org's own homepage, under "Current Adopted Code," lists "Energy Code - 2021 IECC" alongside 2021 IBC, IRC, IMC, IFGC, IPC, IEBC, 2023 NEC, and states the department serves those jurisdictions; the same page links directly to DOE's REScheck tool under "Energy Codes Res Check."⁷

8. Boulder County (unincorporated) = 2021 IECC (with Appendixes CB, CD, RB, RD), effective July 1, 2026. VERIFIED. Boulder County's own "Building Code Amendments" page states: "Building Code Update - Effective July 1, 2026... all new building projects will be reviewed under the 2021 International Codes (I-Codes) along with Boulder County's local amendments," and the county's own approved-amendments PDF lists "2021 International Energy Conservation Code (the 'IECC'), including appendixes CB, CD, RB, and RD" as item 8 of the adopted code package. Applies to unincorporated Boulder County only; incorporated cities/towns within the county (e.g., Boulder, Longmont) adopt independently.⁸

9. Longmont = 2024 IECC (part of the 2024 International Codes plus Metro Cohort Model Code and Colorado Wildfire Resiliency Code), effective July 1, 2026. VERIFIED. Longmont's own "Building Codes" page states: "2024 Code Adoption: The City of Longmont has adopted the 2024 International Codes, along with the Metro Cohort Model Code and Colorado Wildfire Resiliency Code as of July 1st, 2026," and links to the 2024 International Codes and the "2024 Metro Cohort Model Code - based on the 2024 International Energy Conservation Code" directly on the Digital Codes platform (codes.iccsafe.org).⁹

10. Fort Collins = 2024 IECC with local amendments, including a mandatory Path to Zero Carbon (Appendix RZ), effective April 1, 2026. VERIFIED. Fort Collins' own ordinance document ("24-IECC Final Amendments," fortcollins.gov) states: "The City Council hereby repeals the 2021 International Energy Conservation Code ('IECC') and adopts the 2024 IECC as amended by this Ordinance," adopted at second reading December 16, 2025. The city's own "Code Chronology" spreadsheet (code-chronology_july2026.pdf) confirms an April 1, 2026 adoption date entry for the 2024 IECC alongside other 2024 I-Codes.¹⁰

11. Town of Monument (via PPRBD) adopting 2021 IECC + Colorado Model Electric Ready and Solar Ready Code effective June 30, 2026, as a secondary code layered on the Pikes Peak Regional Building Code. VERIFIED. Town of Monument's own news release, "PPRBD Adopts Energy Codes, Effective 6/30/2026," states: "The Pikes Peak Regional Building Department has notified the Town that they will be adopting the 2021 International Energy Conservation Code (IECC) and the Colorado Model Electric Ready and Solar Ready Code (CMERSR), effective June 30, 2026... The IECC and CMERSR are secondary codes and will be enforced under the provisions of the Town of Monument building code."¹¹

12. REScheck supports 2009-2024 IECC editions plus a "Denver (2019)" state-specific edition. VERIFIED (primary source). DOE's own energycodes.gov/rescheck page, supported-codes list (version 4.2.0, October 6, 2025 release): "2009, 2012, 2015, 2018, 2021, and 2024 IECC" plus "State Energy Codes: Florida (2017), Louisiana (2021), Massachusetts (2023), New York City, DC (2017), Denver (2019), Puerto Rico, Utah (2012), Vermont (2020, 2024)."¹²

13. Longmont ADU Submittal Checklist requires "Manual J, D, S" (Manual D waived if no ductwork; Manual J and S required for prescriptive path or equivalent mechanical calcs). VERIFIED (primary source), re-fetched directly. longmontcolorado.gov's own "Accessory Dwelling Unit - Submittal Checklist" PDF, under item 5, "Energy Code Certification," states: "a. Manual J, D, S - If there is no ductwork - such as mini-split system then a manual D is not required. (Manual J & S is required when doing Prescriptive path - or show mechanical calcs for equipment sizing). b. HERS report or ResCheck (not required with a prescriptive path)." The City's newer (2025/2026) ADU Guide repeats the same "Manual J, Manual D, Manual S" line item for Detached ADUs.¹³

14. HB24-1152 (2024): Colorado's statewide ADU law, requiring subject jurisdictions to allow one ADU by-right, effective June 30, 2025. VERIFIED. leg.colorado.gov's own HB24-1152 bill page Bill Summary confirms the by-right ADU requirement for subject jurisdictions (generally municipalities over 1,000 population within a metropolitan planning organization area, or qualifying dense county areas), effective June 30, 2025, plus the associated ADU grant program administered by the Department of Local Affairs. Signed by the Governor May 13, 2024.¹⁴

What remains genuinely unconfirmed: the exact energy code in effect for the dozens of Colorado cities and counties not named on this page; whether every jurisdiction's local amendments to their base IECC edition would change how a REScheck report needs to be structured (only Denver's dedicated REScheck edition and Boulder County's/Fort Collins'/Longmont's appendix lists were directly checked); and the precise permit-application-date cutover rules each jurisdiction applies when its code changes mid-project. Confirm any of these directly with the relevant building department before finalizing a compliance strategy.

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Sources

This page summarizes Colorado's state-law floor on local energy code adoption and six jurisdiction-specific adoptions for general guidance. Because Colorado energy code adoption happens jurisdiction-by-jurisdiction under home rule, requirements for any specific city or county not named here may differ. Always confirm current requirements with your local building department before finalizing design or bidding.