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.
