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Illinois Introduced A Tough New Energy Code Update. Here Is How Buildings Can Comply


Chicagoans and other Midwesterners are anticipating the cyclical return of a historically large cicada brood this spring. But another recurrent event, while far less noisy than the chattering of billions of lovesick insects, is likely to have a much longer-lasting impact, at least on commercial buildings in Chicago.

Since 2004, Illinois has been in the vanguard among states for updating its building energy codes based on standards set by the International Code Council and the American Society of Heating, Refrigerating and Air-Conditioning Engineers. With each code cycle update, the standards have become more stringent to reach the goal of net-zero building energy by 2030. 

The latest update in Illinois went into effect on Jan. 1. As building envelope insulation requirements reach their point of diminishing returns, the codes have to look to other areas to eke out additional energy savings, said Allison McSherry, an architect and associate with Klein & Hoffman, a Chicago-based structural and architectural engineering firm. 

One of these areas is continuous air barriers, which have been a requirement for many code iterations. But how the continuous air barrier is verified has changed. For the first time, whole building air barrier testing is required unless building envelope performance verification, known as BEPV, is performed to the requirements of both 2021 IECC and ASHRAE 90.1-2019.

McSherry and Project Architect and principal Glenn Johnson of Klein & Hoffman spoke with Bisnow about how buildings in the Windy City can prepare for and avoid being bugged by the code changes.

Which Path Is Right For You?

There are two main paths a project team can follow to meet the continuous air barrier verification requirements. 

One is to conduct whole building air barrier testing of the finished or nearly finished structure. Known as the blower door option, this entails temporarily shutting down access to the building and then testing the building’s air tightness by applying negative or positive pressure to its interior via large fans and measuring how much air is leaked through the building’s envelope.

Johnson said this is a fairly simple process for small buildings. But it can be time-consuming, expensive and inconvenient to perform on a finished high-rise, even if the building is not required to test every floor. Plus, if any leakages come to light, the building owner will have to take expensive steps to improve the air barrier of a completed building.

“You have to decide whether you want to gamble with the blower door process and wait until the end of construction to find out if you have a problem,” he said. “Or, do you want to be proactive and not risk having this issue?”

BEPV is an alternative approach that combines a design review of the air barrier details with site visits during construction to ensure the air barrier is being installed properly. 

“We feel that for large, complex building types, the BEPV approach provides a much better cost/value proposition for the project,” McSherry said. “A document review provides an opportunity to correct detailing, and in-progress construction site visits allow confirmation that the air barrier is being installed correctly.”

No matter which route an owner decides is best for a building, McSherry said now is the time to take these code requirements seriously. Like the cicadas, the more stringent IECC and ASHRAE 90.1 requirements have emerged and cannot be ignored whether Chicago building owners like it or not.

“A lot of people don’t even know about this requirement yet, but you have to begin early to achieve compliance,” Johnson said. “The longer you wait, the more redesign work has to be done, and it becomes harder to make changes to bring the building into compliance. You might find you’re spending more money than you would have had you been proactive. The choice is between being proactive or reactive.”

WHat the future holds

The next code cycle, 2024 IECC and ASHRAE 90.1-2022, has even more complex requirements. For example, ASHRAE 90.1-2022 has introduced an envelope backstop, which limits performance trade-offs to between envelope components only instead of the previously allowed trade-offs with HVAC and lighting. 

“That has never been done before in Illinois, and it’s a huge deal because our buildings either have to go back to having more opacity, like our older masonry buildings, or, we’ll potentially be looking at triple-glazed or vacuum-insulated glazing for windows,” McSherry said.

Owners and architects need to be aware these upcoming changes will impact both their processes and, potentially, their costs, McSherry said. 

“A lot of owners like the all-glass look, but you obviously can get more insulation value out of an opaque wall than you can out of a window,” she said. 

McSherry said the energy codes already limit the amount of window-to-wall ratio, but the envelope backstop means that building owners can no longer rely on HVAC and lighting to offset a high window-to-wall ratio. This requires a balance between what they want to do aesthetically and the need to meet the code. 

Short term, McSherry said, this will impact how owners work to ensure their buildings are in compliance. Longer term, it could affect the design and look of next-generation buildings.

This does not mean that future Chicago buildings will resemble the stone-clad skyscrapers of a century ago, she added. But it will have architects and owners looking at alternatives to curtain walls, such as opaque walls with punched openings for windows or more unique fenestration designs per facade.

Curtain walls are problematic from an energy perspective, particularly spandrel panels, which McSherry called the “weakest link” in curtain wall energy leakage, or in places where balconies are attached to the facade. 

This is due to the impact of thermal bridging: heat flow that follows the path of least resistance through an assembly. The next code cycle will also address thermal bridging in the energy codes for the first time, she said. However, Chicago is ahead of the game with the 2022 Chicago Energy Transformation Code, which went into effect in November 2023 and already addresses thermal bridging for balconies and parapet walls. 

Most project teams don’t have a staff energy expert staying up to date with the nuances of the evolving energy code requirements. For that reason — and because owners don’t have the luxury of laying low for several years like the cicadas — McSherry recommended they sit down now with their architects and other experts to dig into the best way to ensure compliance while taking into consideration the desired design aesthetic. 

“The nuances of compliance are becoming increasingly complex as code requirements ratchet down lower,” she said. “For that reason, there needs to be a much more collaborative process involving the building owner, architect and MEP engineer because achieving compliance will inevitably involve trade-offs between design intent and what is allowable by the energy codes.”  

This article was produced in collaboration between Klein & Hoffman and Studio B. Bisnow news staff was not involved in the production of this content.

Studio B is Bisnow’s in-house content and design studio. To learn more about how Studio B can help your team, reach out to