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.
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.
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:
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.
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:
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:
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.
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.
