Increased Energy Performance Requirements on the Horizon in ASHRAE 90.1-2019

Tom Culp
July 18, 2018

NGA LogoThis article presents the changes to ASHRAE 90.1 that will have the greatest impact on the glass and glazing industry. 

Next step in stringency for U-factor and SHGC

The industry will see the next step in stringency for U-factor and solar heat gain coefficient requirements for glass and glazing in the 2019 version.

What happened:

Proposals were advanced for ASHRAE 90.1-2019 at the ASHRAE summer meeting, with several notable changes on tap for the commercial glass and glazing industry. Key changes include more stringent requirements for thermal efficiency and solar control and removal of metal versus nonmetal distinctions. The meeting also included discussion of potential new proposals that, if done incorrectly, could limit window area.

Why it matters:

ASHRAE 90.1 is the benchmark for commercial building energy codes in the United States and a key basis for codes and standards around the world. The changes to the standard find their way into the codes, which dictate performance requirements for windows in all nonresidential buildings and residential buildings four stories or higher.

ASHRAE is nearing completion of the 2019 criteria for its 90.1 commercial building energy code standard, with several notable changes on the horizon for the glass and glazing industry. The determinations from the standard will likely form the basis for the 2021 International Energy Conservation Code proposals, making it essential for industry companies to be aware of updates to the standard. 

After months of analysis and negotiation, various industry representatives and key stakeholders agreed upon a set of requirements that will continue the trend of increased stringency in the energy codes, while also being practical and cost-effective. U-factors decreased 5 to 15 percent between the 2013 and 2016 versions, and this downward trajectory will continue in 90.1-2019, with U-factor requirements decreasing another 5 percent and 17 percent in the various climate zones.  

SHGC requirements also saw modest reductions across most climate zones, although they are not expected to cause drastic changes in glazing type from what is currently used. Solar control products will be needed in many locations, with lower SHGC in the south. 

One new change is that the requirements will list separate SHGC criteria for fixed and operable products, just like the standards already do for U-factor. Importantly, this will not require different glazing for fixed and operable products, but will allow the committee to capture some unclaimed energy savings due to the fact that operable products inherently have a lower SHGC than fixed products even with the same glazing, due to the larger frame percentage. 

What might this mean for the glass and glazing industry in terms of the types of products that likely would be required in the various climate zones? In a very rough sense, this represents a “zone shift,” with northern products moving a notch south. For example, what was currently required in Zone 7 would now be required in Zone 6, Zone 6 moves to Zone 5, etc. Overall, this will continue to push more advanced thermal breaks, warm-edge spacers, argon gas fill and 4th surface low-emissivity products. 

In the warm weather climate of Zone 1, the industry will likely see the need for low-E double glazing with lower SHGC, such as the newest triple silver low-E products. Zones 2-3 will likely see low-E double glazing in a thermally broken frame, and potentially the use of argon fill. In Zones 4-5, low-E double glazing in a thermally broken frame will be required, along with two of the following: argon-fill, high-performance thermal break or two low-E coatings (No. 2 and No. 4 surface). Zone 6 will also require low-E double glazing in a thermally broken frame with three of the following: argon-fill, warm-edge spacer, high-performance thermal break or the two low-E coatings. Zone 7 would require all the options listed in Zone 6, or will move to triple glazing. In Zone 8, triple glazing will likely be required. 

Elimination of material distinctions

Existing versions of ASHRAE 90.1 include separate U-factor requirements for nonmetal versus metal glazing systems. The IECC previously had this distinction based on frame material, but it was removed in 2012. As part of the overall proposal for ASHRAE 90.1-2019, there was agreement to match the ASHRAE 90.1 product categories to those used in the IECC. This results in separate U-factors for fixed windows, operable windows, entrance doors and skylights without regard to material type. 

This issue has been debated at ASHRAE for 14 years. It was agreed to resolve this issue in part because of the realization that the real-world market impact is small, as architects choose different window products appropriate for their particular application, not because of what the code category says. Additionally, the change will improve consistency with the IECC.  

New limits on window area?

In the 2010 and 2013 versions of ASHRAE 90.1 and the 2014 version of ASHRAE 189.1, the glass and glazing industry fought back proposals that would have reduced the window-to-wall ratio from 40 percent to 30 percent on projects going through the prescriptive path. The industry won these battles by demonstrating how reduced window area would actually be contradictory to high-performance buildings, where access to quality daylighting and views improves overall functionality, health and wellness of occupants.  

The industry has not seen such direct attacks on window area since that time. However, proposals to limit window area are potentially taking a different shape. While there were no specific proposals voted on at the ASHRAE meeting, there were discussions about introducing new restrictions on the performance path in ASHRAE 90.1 that limit trade-offs within the envelope. If done incorrectly, these limits could create an artificial barrier that would limit window area, even if equivalent or superior overall energy efficiency is shown.  

One suggestion was a direct limit on the envelope performance—a certain performance level that the envelope can’t fall below when making other trade-offs in lighting and mechanical systems. The devil is in the details on how this would be done, and the impact on window area and building performance is unclear. It may be a solution in search of a problem that doesn’t exist, since the overall building energy efficiency is the same. This will be an important issue for the industry to continue monitoring. 

What’s next?

The ASHRAE 90.1 committee unanimously approved the proposed U-factor and SHGC changes to go out for public review, which will likely occur in August. As the proposal achieved broad consensus, there should not be many comments, but any comments received will be addressed at ASHRAE 90.1’s next meeting in October.  

Tom Culp is a technical code consultant for the National Glass Association and the Aluminum Extruders Council, and is the owner of Birch Point Consulting. He can be reached at