By: Glenn Mathewson
Colorado energy code updates 2025
From the farmers in the Eastern plains, across the city slickers of the front range, up in elevation to the foothill commuters, through the high country and resort towns, past the rural mountain communities, and down the mountains to the Western slopes, Colorado climates, communities, and lifestyles are not the same.
Building codes and other regulatory subjects reflect this diversity. Colorado is what’s called a “home-rule” state. This means there’re no state-wide building or energy codes. Instead, individual jurisdictions set their own requirements. So, if you live in one of the 15 counties that haven’t adopted a building code, it’s all up to you to how you build … sort of.
Colorado has statewide plumbing and electrical codes. Recently, an energy code with statewide implications was adopted. A year later, a second piece of legislation was adopted that created confusion. If you’re trying to understand how to specify windows and doors in Colorado, here’s what you need to know.
Colorado’s new energy code
In 2022, House Bill 22-1362 provided the legislative authority and directive for the creation of a Colorado Energy Board responsible for creating a model electric-ready code, solar-ready code, and a low-energy and carbon code utilizing the more efficient of the 2021 and 2024 International Energy Conservation Code. The model codes created by the new Colorado Energy Board are relatively straightforward, except when it comes to windows and doors, as you’ll see in just a minute.
Importantly, Colorado is still a home-rule state and building codes are still set by local jurisdictions, but individual jurisdictions are now required to adopt the new state energy code when they update their building code.
TIP: The Colorado Energy Office (CEO) created resources to aid jurisdictions in adoption, including trainings for both the building authority personnel and the public, and the free Colorado Code Helpline. Explore these resources.
Point-of-sale legislation for windows, skylights, and doors
In 2023, the state passed a bill, House Bill 23-1161, including energy efficiency standards for residential windows and doors that are sold in Colorado. This created confusion because standards for windows and doors were already provided in the Model Low Energy and Carbon Code created by the CEO. And as we’ll discover, the standards aren’t the same.
House Bill 23-1161 stated:
(5) On and after January 1, 2026, a person shall not sell, offer to sell, lease, or offer to lease any of the following new products in Colorado unless the efficiency of the new product meets or exceeds the following efficiency standards, as applicable
(j) Residential windows, residential doors, and residential skylights included in the scope of the Energy Star Program product specification for residential windows, doors, and skylights must satisfy the northern climate zone qualification criteria of that specification; except that residential windows and doors that are custom designed for a historically designated building and required in order to maintain the historic nature or character of such a building are not required to satisfy such criteria.
The current standards of ENERGY STAR® version 7.0 include substantial performance requirements for northern climates that provide tremendous thermal performance. Here are the minimum standards for the Northern climate zone:
- Residential windows: Max 0.26 U-Factor (including limitations on SHGC)
- Residential skylights: Max 0.45 U-Factor
- Residential doors (>1/2 lite): Max 0.26 U-Factor (including limitations on SHGC)
- Residential doors (<1/2 lite): Max 0.23 U-Factor[JM2.1][VA2.2][JM2.3][GM2.4] (including limitations on SHGC)
These maximum allowable U-Factor values are quite low (more efficient) compared to the norm in Colorado and were a shock to not only builders, as one might expect, but also window manufacturers and even local building officials. Further complicating the situation, northern climates also have requirements for solar heat gain coefficient (SHGC) under the ENERGY STAR® Program. For example, a window with a 0.26 U-Factor must have a 0.40 or greater SHGC. A window with a 0.22 U-Factor can have a SHGC as low as 0.17. The intent behind this is when a window allows more heat gain through solar radiation (higher SHGC), it can allow slightly more heat loss through the window assembly via conduction/convection (higher U-Factor). These requirements are more stringent than any edition of the International Energy Conservation Code (IECC), which has been historically used as the basis for the energy codes used throughout Colorado jurisdictions.
One issue complicating the adoption of ENERGY STAR® performance requirements in Colorado specifically is that window manufacturers often use inert gases between the panes of glass to improve U-Factor values (Andersen uses an argon-gas blend). However, the high elevations of Colorado have a different air pressure than where most windows are manufactured, which means windows for high elevations often must be ordered without the gas infill. This means it can be tricky to achieve ENERGY STAR required U-Factor values without increasing to triple glazing or other innovations. This ultimately limits consumer choices at high altitudes.
Another issue with the bill is that it specifically regulates the “sell[ing] and leas[ing]” of windows as a product but doesn’t refer to their installation.
Perhaps the legislators knew these requirements would be a challenge to the industry, as they signed it into law in 2023, but it wasn’t to be effective until January 1, 2026. This gave ample time for the public to respond and the lawmakers to listen.
Reconsidering the standard
In 2024, Senate Bill 24-214 was adopted granting the Executive Director of the Colorado Department of Public Health and Environment (CDPHE) the authority to consult with the CEO to evaluate an alternative standard if the ENERGY STAR standard enacted by Congress could not be reasonably met. The evaluation was performed and led the CEO to issue the following statement:
“The standard cannot be met by manufacturers without imposing too high of a financial burden on the majority of Colorado households.”
The CEO concluded the ENERGY STAR standard would cause the following concerns:
- It would eliminate the use of solid wood doors due to the low U-Factor values required.
- It would eliminate the option for designers to use the weight-average method of energy performance where the performance of certain windows is increased, allowing others to be decreased. Lower-performing windows wouldn’t be allowed for purchase, and higher-performing windows wouldn’t likely be found. The flexibility of design resulting from performance “trade-offs” has been a popular option in the code since the first Model Energy Code was published in 1977. Thus, removing that option is not ideal.
- It would reduce window selection for those living above 9,000 feet of elevation, a significant segment of Colorado’s population.
The CEO recommended an alternative standard to be used for this legislative requirement, and the alternative standard was more closely aligned with the 2024 International Energy Conservation Code as opposed to the ENERGY STAR version 7.0 Northern climate specification. This is the same code referenced by the CEO’s new Model Low Energy and Carbon Code. Things are starting to make sense. If the statewide point-of-sale regulations match the installation requirements of the state energy code, it’s easier for the public to comply with both regulations.
More specifically, the alternative performance thresholds recommended by the CEO were for no windows to be sold in Colorado with a U-Factor value greater than what’s allowed by the prescriptive method of compliance in the 2024 IECC for Climate Zone 5, which is the lowest value climate zone in Colorado. Those values are as follows:
- Residential windows: Max 0.30 U-Factor
- Residential skylights: Max 0.50 U-Factor
- Residential doors (>1/2 lite): Max 0.30 U-Factor
- Residential doors (<1/2 lite): Exempt from U-Factor requirements
Additionally, the CEO recommendation was to not regulate the solar heat gain coefficient (SHGC), as it is not useful for all designs in all Colorado regions. In Climate Zone 5 regions, a low SHGC value is useful to offset summer cooling, but in colder climates and with passive house design concepts, a high SHGC value is useful to offset winter heating. Thus, it’s best to let the designer decide the ideal SHGC value for the project. The CEO also recommended that opaque doors and doors with less than ½ lite glass be exempted from the U-Factor requirements. This exemption provides flexibility for builders and homeowners that want to install character-defining wood doors, fire doors, or security doors that can’t achieve U-Factors of 0.30 or lower.
The state is moving forward with the revised point-of-sale thermal performance requirements recommended by the CEO. They are set to take effect on January 1, 2026.
To find the Andersen® products that can meet thermal performance requirements in your jurisdiction, reach out to your local dealer.
Your FAQs about Colorado’s energy code changes answered
Can homeowners be punished for installing windows, doors, or skylights that are not compliant with the new statewide efficiency requirements?
No, a homeowner won’t be punished, fined, or penalized if they purchase and install a non-compliant window, door, or skylight product in their home. The statewide HB23-1161 standard is a point-of-sale standard enforced at the retail level. Thus, retailers/distributors/manufacturers selling window, door, and skylight products in Colorado or entities involved in the sale of window, door, and skylight installation services in Colorado are the entities that must ensure they’re selling products that comply with the standard.
How can I improve my window’s U-Factor?
Ordering windows for high elevations sometimes requires specifying without the argon-gas blend infill that Andersen uses to improve the insulating abilities of our window glass. Still, you can make selections that will improve your window’s performance. Here’s what to keep in mind:
- Window types: Select picture windows where possible and casement and awning windows where operability is needed.
- Low-emissivity coating (Low-E): Select the right Low-E coating or combination of coatings to optimize your window’s performance.
- Triple-pane glass: With an additional air space and the opportunity for up to three Low-E coatings, this is the best performing glass option.
Find performance data, including U-Factor ratings for various window and door configurations.
What are the new requirements for windows and doors in Colorado?
To comply with the 2023 point-of-sale bill, windows and doors sold in Colorado will be required to meet these U-Factor values starting January 1, 2026:
- Windows: ≤ 0.30 U-Factor
- Skylights: ≤ 0.50 U-Factor
- Residential doors with >½-light glazing: ≤ 0.30 U-Factor
- Opaque and ≤1/2-light glazing: Exempt from U-Factor requirements
There are no SHGC value requirements. Remember that Colorado is a home-rule state, meaning energy code is set by local jurisdictions, so you must check with your local code authority.
At what altitude is a breather tube required?
Generally, at altitudes above 4,000’, Andersen recommends windows be ordered without an argon-gas blend fill and with a breather tube. This has an effect on a window’s energy efficiency, of course.
If you’re trying to achieve a lower U-Factor value, we have altitude limit charts that can be used as a reference. These charts can help you to understand how unit size impacts the need for this high-altitude adjustment.
In some cases, it might be possible to mix and match window and door products — to include some with the high-altitude adjustment and some with argon-gas blend. This approach can sometimes be used to meet energy requirements.
Here are our altitude charts by product line:
What products are available with triple-pane glass?
Andersen offers a variety of windows and doors with triple-pane glass, including:
- A-Series windows and doors are available with triple-pane glass.
- E-Series windows and doors are available with triple-pane glass.
- 400 Series windows and doors are available with triple-pane glass in select states.
- Select 200 Series doors are available with triple-pane glass.
- Select 100 Series windows will be available with triple-pane glass on October 20.
- All Big Doors, including Folding Outswing, MultiGlide™, and Liftslide Doors, are available with triple-pane glass.
What does ENERGY STAR v. 7.0 mean for Colorado?
Although Colorado didn’t adopt ENERGY STAR v. 7.0 performance requirements into its point-of-sale law, windows and doors that meet the requirements of this version of ENERGY STAR are compliant — because, of course, they go beyond requirements.
For homeowners who wish to build to the highest standards of efficiency for sustainability, comfort, or other reasons, products that meet these rigorous standards might be the right choice. We make windows and doors that meet ENERGY STAR v. 7.0 requirements. Find out more about ENERGY STAR v. 7.0 and the products that meet its standards.
Windows that meet ENERGY STAR’s Most Efficient criteria and were installed in the 2025 calendar year are eligible for a tax credit. Find out more about the tax credit.
Meet Glenn
Glenn was a tradesman in the late 1990s before becoming a city building inspector in 2005. During that time, he was teaching, writing, and consulting in codes on the side, and it became his full-time work in 2018. He has published over 100 technical articles, including his current column in Fine Homebuilding Magazine. He is an educational book author for ICC and an author for the popular CodeCheck publications. He teaches building codes across the country and online through his website, BuildingCodeCollege.com. Glenn was awarded ICC Educator of the year in 2021. He assists local Colorado governments in updating their adopted codes, as well as a variety of other educational consulting.
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