Energy codes vary by state in the United States, and the code that governs your project is whichever edition of the International Energy Conservation Code or ASHRAE Standard 90.1 your state (or in some cases your city or county) has formally adopted. As of mid-2025, more than half the states still enforce codes based on the 2009 IECC or earlier, while Rhode Island has moved to the 2024 edition and a handful of others are in review. “Code-compliant” in one state can describe a building that would fail inspection a state line away.
Finding the Code That Applies to Your Project
Start with the Department of Energy’s Building Energy Codes Program, which tracks adoption status for all 50 states at energycodes.gov.1Department of Energy. Building Energy Codes Program That tells you the state baseline. It does not tell you the whole story.
If your state operates under home rule, the city or county may enforce a different edition or add local amendments on top of the state code. A project on one side of a county line can face entirely different insulation or air-sealing requirements than one a few miles away. A growing number of cities also adopt a stretch code, meaning a code based on the current or upcoming model edition with stricter efficiency measures layered in. Where a stretch code is in force, those stricter provisions supersede the state baseline for permit purposes.
Before architectural plans are finalized, contact the local building department and ask in writing for three things: the specific code edition in force, any local amendments, and the effective date. State building commission websites often publish the full text of amendments. Pay attention to the gap between an adopted code and an effective code. Legislatures sometimes pass a new code with a delayed effective date, and inspections may apply the code in force at the time of inspection rather than at permit issuance. An hour of verification up front can prevent weeks of redesign.
Why States Are on Different Editions
The model codes come from two sources. The IECC covers residential construction. ASHRAE Standard 90.1 covers commercial. Both are updated on a three-year cycle.2Building Energy Codes Program. href=”https://www.energycodes.gov/commercial-and-residential-building-energy-codes” target=”_blank” rel=”noopener”>Commercial and Residential Building Energy Codes
Federal law under 42 U.S.C. ยง 6833 requires each state to review its energy code whenever a new model edition is published and certify to DOE whether it will update.3Office of the Law Revision Counsel. 42 US Code 6833 – Updating State Building Energy Efficiency Codes The statute requires review and certification. It does not require adoption. A state can decide its current code is adequate and decline to update, and many do. States can also amend a model code, adopt only portions of it, or write their own. That is why neighboring states sometimes enforce codes published more than a decade apart.
Residential or Commercial: Which Code Applies
The split hinges on building height, not use. Residential energy codes under the IECC apply to detached houses, townhouses, duplexes, and multifamily buildings three stories or fewer above grade. Once a residential-occupancy building reaches four stories, it falls under the commercial code, ASHRAE 90.1, which has different lighting, mechanical, and envelope requirements.4Building Energy Codes Program. Commercial and Residential Building Energy Codes
A four-story apartment complex follows ASHRAE 90.1, not the IECC residential provisions, even though every unit is someone’s home.5Department of Energy. The New Energy Code for Commercial Buildings: Standard 90.1-2016 A jurisdiction can also sit on different editions for each side: current residential code, older commercial code. Misclassifying a project at the outset leads to rejection during plan review, because the wrong code produces the wrong insulation values, lighting calculations, and mechanical specifications.
How You Prove Compliance
Energy codes typically offer more than one way to show a building meets the standard. The pathway you choose affects design flexibility, documentation, and whether you need third-party testing.
Prescriptive Path
Each building component must individually hit a specific value in the code: a wall with at least R-20 insulation, windows with a U-factor no higher than 0.30, and so on. There is no flexibility to trade off one component against another. If one component falls short, it fails regardless of how the rest of the building performs. The upside is that compliance can be verified without energy modeling software.
Performance Path
Here the building is evaluated as a whole. Under the IECC, you demonstrate that the proposed design’s annual energy cost is equal to or less than a prescriptive-compliant version of the same building. That lets you install slightly less insulation in one area if you compensate with better windows or a higher-efficiency HVAC system elsewhere. The cost is complexity: energy modeling software, and sometimes a third-party energy rater to verify results.6Building Energy Codes Program. ASHRAE Standard 90.1 Performance Based Compliance (Section 12 and Appendix G)
Energy Rating Index Path
Available for residential projects where the jurisdiction has adopted it. The Energy Rating Index runs 0 to 100, with 100 as a home built to the 2006 IECC baseline and 0 as net-zero. The code sets a maximum ERI score (often in the low 60s depending on climate zone), meaning the home must use roughly 40% less energy than the 2006 baseline. A certified third-party rater runs the calculations, performs on-site blower door and duct leakage tests, and issues a compliance report. Even under the ERI path, certain mandatory requirements still apply: air leakage testing, mechanical ventilation, equipment sizing, and pipe insulation.
The Tests and Numbers That Decide Inspections
A few requirements come up in almost every residential energy code inspection and account for most of the holdups.
Air leakage is measured with a blower door, which pressurizes or depressurizes the house to measure how much air escapes through gaps in the envelope. The national IECC threshold is typically 3 air changes per hour at 50 Pascals, though some states and climate zones set a different number. Failed blower door tests are one of the most common inspection problems in new construction, usually from unsealed penetrations around wiring, plumbing, or recessed lights.
Duct leakage is a separate pressure test that measures conditioned air escaping from the ductwork before it reaches the rooms it is meant to serve. Testing typically runs $175 to $300 for new residential work and is frequently the difference between passing and failing.
Required R-values for insulation and U-factors for windows vary by climate zone, with colder zones demanding more. These numbers also change between code editions, so verify them against the exact code version your jurisdiction enforces rather than relying on general values.
If your jurisdiction has adopted the 2021 or 2024 IECC, check for solar-ready and electric-vehicle-ready provisions early in design. These require infrastructure (panel capacity, conduit, sometimes full circuits) for future solar or EV charging even when neither system is installed at construction. On the commercial side, the 2024 IECC sets three tiers of EV readiness for parking facilities and requires at least 7.2 kVA per space (or 3.3 kVA with an energy management system), with branch circuits rated 50 amperes minimum (25 amperes with energy management).7Energy Codes. IECC EV Charging Infrastructure Requirements These provisions drive electrical panel sizing and conduit runs, both hard to retrofit.
What Happens If You Miss
Enforcement generally progresses from plan review rejection to failed inspections, stop-work orders, fines, and ultimately denial of a certificate of occupancy. The CO is the one that bites hardest. A building that passes structural and fire inspections but fails on insulation, air sealing, or mechanical efficiency will not receive a certificate of occupancy, and no building can be legally occupied without one. For a developer carrying construction loans, every day without a CO is a day of interest on a building that cannot generate revenue.
Fines range from a few hundred to several thousand dollars per day depending on jurisdiction and project size. Some jurisdictions can also revoke or suspend building permits for ongoing non-compliance. A stop-work order halts construction entirely until the violation is corrected, which cascades into missed deadlines with subcontractors and suppliers.
Federal Tax Credits for Exceeding Code
Two federal incentives reward construction that goes beyond the minimum. Both are currently set to expire on June 30, 2026.
Section 45L is a credit for builders of new homes and apartments meeting Energy Star certification. For single-family and manufactured homes, the credit is $2,500 per unit for Energy Star certification or $5,000 per unit for a DOE Zero Energy Ready Home. For multifamily units, it is $500 per unit (Energy Star) or $1,000 per unit (Zero Energy Ready), rising to $2,500 and $5,000 respectively when prevailing wage requirements are met during construction. To qualify in 2026, single-family homes must meet Energy Star Single-Family New Homes National Program Requirements version 3.2 and the most recent Energy Star standards applicable to the location. The credit applies only to homes acquired before July 1, 2026.8Office of the Law Revision Counsel. 26 USC 45L: New Energy Efficient Home Credit
Section 179D is a deduction for commercial building owners and designers whose buildings or systems exceed the ASHRAE 90.1 reference standard by specified percentages. The maximum can reach approximately $5.00 or more per square foot at the highest efficiency thresholds. Like 45L, 179D is set to expire for projects that do not begin construction before July 1, 2026. Confirm the current status of both before relying on them in a pro forma, since Congress may extend or modify either.