Information · Energy Codes, U.S. & Canada
Energy Codes, U.S. & Canada
How energy codes work in the United States
The United States has no national building code. Instead, private organizations write model codes, and states and local governments adopt them into law, often with their own amendments.
- The International Energy Conservation Code (IECC), published by the International Code Council (ICC) every three years, is the model energy code for most of the country. It has a residential part, for houses and low-rise residential buildings up to three stories, and a commercial part for everything else.
- ASHRAE Standard 90.1 is the commercial energy standard written by ASHRAE. The IECC accepts it as an alternative path for commercial buildings, and it is the baseline for LEED energy modeling.
- The building department of each city, town or county, the “authority having jurisdiction,” enforces whatever its state or locality has adopted, through plan review and inspection.
Codes divide the country into climate zones, from 0 (hottest) to 8 (coldest), with moisture regimes marked A (humid), B (dry) and C (marine). Window requirements tighten as zones get colder.
What codes ask of windows
Under the prescriptive path, each window must meet a maximum U-factor and, in warm zones, a maximum SHGC, using NFRC-certified ratings. Under performance paths, designers can trade better windows against other parts of the building in an energy model. For example, the 2021 IECC residential prescriptive limits are:
| 2021 IECC residential, climate zone | Max fenestration U-factor | Max SHGC |
|---|---|---|
| 0 and 1 | 0.50 | 0.25 |
| 2 | 0.40 | 0.25 |
| 3 | 0.30 | 0.25 |
| 4 (except marine) | 0.30 | 0.40 |
| 5 to 8, and 4 marine | 0.30 | No requirement |
Commercial codes also set U-factor and SHGC limits by climate zone, separately for fixed and operable windows, and limit window-to-wall ratio on the prescriptive path, typically to 30 to 40% of the wall area depending on the code and on daylighting controls. Buildings with more glass must show compliance by energy modeling, which is where high-performance windows make the difference. Most codes also require air leakage testing or ratings for windows.
For comparison, our GR85 fixed window with ZERO 04 glass calculates at 0.085 Btu/h·ft²·°F, well under a third of the strictest limit above.
Who has adopted what
Because each state adopts its own code, the map is uneven. As of 2026:
- Most states enforce the 2018 or 2021 IECC, or their own codes based on them, for both homes and commercial buildings.
- The 2024 IECC is beginning to be adopted. Illinois and Rhode Island have adopted it, Colorado’s modified version takes effect in July 2026, and Connecticut, Delaware, Maine, Maryland, Massachusetts, New Jersey and New York are pursuing it.
- Some states pause updates. California and North Carolina have frozen residential code updates until 2031, and bills to freeze or cap codes have been introduced in other states.
- States set their own codes. California writes its own energy code, Title 24, Part 6, updated every three years; the 2025 edition took effect on January 1, 2026. Washington and Oregon also write their own codes, among the strictest in the country.
Where codes are weak or absent
In some states there is no mandatory statewide residential energy code. Codes are left to each city or county (“home rule”) or are voluntary, so requirements can range from a recent IECC in a large city to none at all in a rural county. These include Alaska, Arizona, Kansas, Mississippi, Missouri, North Dakota, South Dakota and Wyoming. Colorado was in this group until its new statewide minimum code takes effect in 2026.
Even in states with codes, many rural and unincorporated areas have no building department to enforce them. There, the practical requirements often come from lenders, insurers and buyers rather than inspectors.
Where codes go further
- Stretch codes are optional, stricter codes that municipalities can adopt. Massachusetts has had one since 2009, and its Specialized Opt-in Code, adopted by dozens of municipalities, requires larger multifamily buildings to meet Passive House standards. New York (NYStretch) and Illinois offer stretch codes too.
- Building performance standards set limits on the energy use or emissions of existing buildings, such as New York City’s Local Law 97 and Boston’s BERDO. They make window replacement part of long-term compliance plans.
- Hurricane codes. The Florida Building Code applies statewide, with the strictest wind and impact requirements in the High Velocity Hurricane Zone of Miami-Dade and Broward counties. Windows there need a Florida Product Approval or a Miami-Dade Notice of Acceptance; see our A-Series.
Where U.S. codes are heading
Codes keep tightening, but more slowly and less evenly than they did a few years ago. The 2027 IECC is being developed under a new standards-based process, with publication targeted for the end of 2026, and a proposal for the 2030 edition would split it into a core code and an optional, more ambitious “expanded” tier. Electrification readiness, electric vehicle charging and limits on embodied carbon are the main new themes, while some states push back on the cost and pace of change.
Canada
Canada’s system works much like the U.S. one, with a national model and provincial adoption. The National Research Council publishes the National Building Code (NBC) and the National Energy Code of Canada for Buildings (NECB) about every five years, and each province and territory adopts them, usually with changes. The 2025 editions are now published; most provinces are still on the 2020 editions.
- Tiered energy codes. The 2020 codes introduced performance tiers: Tiers 1 to 5 for houses and small buildings (NBC Section 9.36) and Tiers 1 to 4 for larger buildings (NECB). Provinces choose a tier and a schedule for moving up. Nova Scotia, for example, moves houses to Tier 2 in April 2026 and Tier 3 in April 2027.
- British Columbia uses its own BC Energy Step Code, with steps that lead to net-zero-energy-ready buildings, and a Zero Carbon Step Code for emissions. Many municipalities require higher steps than the provincial minimum.
- Ontario sets its own Ontario Building Code; Toronto adds the Toronto Green Standard for new development. Quebec also adopts the national codes with its own changes.
- Newfoundland and Labrador is the first province to enforce the NBC 2025, from July 2026.
Windows in Canada. Windows must meet the North American Fenestration Standard (NAFS) with its Canadian Supplement for structural, air and water performance. Thermal performance is rated under CSA A440.2, by U-factor or by Energy Rating (ER). Under the prescriptive path of NBC Section 9.36, maximum window U-values range from 1.80 W/m²K in climate zone 4 to 1.40 in zones 7B and 8, and the higher tiers and Step Code levels push well below that.
What this means for your project
Start with the code your jurisdiction actually enforces, including local amendments and any stretch code, then check whether the owner, a funding program or a certification asks for more. If your project is pursuing Passive House, Phius, LEED or a high Step Code level, the windows are usually what decides it. Tell us where your project is and what it is targeting, and we will match the window and glass package to it.
Adoption status summarized from ACEEE’s state energy code database, the Institute for Market Transformation’s 2026 Energy Codes Outlook and the Canadian Board for Harmonized Construction Codes, as of 2026. Code adoption changes often; always confirm with the local building department.