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The First United Bank in Moore, Oklahoma, was designed by Gensler to support the comfort and well-being of all occupants, all while being sustainable. A three-story and 12,000-square-foot steel-framed glass curtain wall wraps around the bank’s mass timber structure. The high-performance curtain wall assembly was designed to create uninhibited sightlines to facilitate community engagement.

The glass industry plays an essential role in addressing the climate crisis. Buildings account for an estimated 40% of the problem of global carbon emissions, with building operations alone producing 27% of total emissions, according to Architecture 2030.

Glass is a critical component in addressing operational carbon emissions by reducing energy use in existing and new buildings. A recent study from Glass for Europe emphasized the difference high-performance glazing can make:

• Replacing all existing windows with “readily available high-performance glazing” by 2030 would cut annual energy use by 29% and annual carbon emissions by 28%.
• Replacing all existing windows with “improved high-performance glazing” by 2050 would cut annual energy use and carbon emissions both by 37%.

Stephen Selkowitz, principal of Stephen Selkowitz Consultants and affiliate at Lawrence Berkeley National Laboratory, estimates similarly dramatic savings for the United States if all existing commercial windows were “magically” retrofitted with next-generation glass technologies, such as highly insulating dynamic glass. “If we convert all windows, we move from a net drain of $20 billion [in energy costs] to a net gain of up to $15 billion [in energy savings],” he explains.

This multi-part article takes a deep dive into the role of glass and glazing in improving building energy and thermal performance and sustainability. It includes a broad look at considerations for carbon reduction with glass; an overview of relevant building codes, standards and regulations and how they are driving performance improvements in façade systems; details on the payback of high-performance systems and retrofits; best practices for using Environmental Product Declarations, or EPDs, for glass; opportunities and challenges of glass recycling; and an overview of existing glass product solutions for next-generation performance.

Steps to Carbon Reduction

The following is based on a panel discussion among glass industry experts, “Blueprint for Collaboration: The path towards sustainable facades,” hosted by the National Glass Association during the week of AIA A’23 in San Francisco.

Photo courtesy of Quanex

Økern Portal in Norway features more than 32,000 square feet of triple glazing to meet thermal, safety, and sound requirements. Twelve different glass assemblies were produced with e warm-edge spacers in sizes up to 47 inches by 118 inches. The outer panes have a highly translucent, color-neutral solar control coating, while the inside has tempered or laminated glass in various thicknesses.

Improving building sustainability and reducing carbon emissions requires a move away from business as usual. For the glass industry, industry officials identify three key areas of focus.

Reduce Embodied Carbon

Embodied carbon in construction refers to greenhouse gas emissions caused during the lifecycle of a building product, including raw material extraction, transportation, manufacturing and installation. For the glass industry, the energy-intensive glass manufacturing process is the primary source of embodied carbon.

“Where does embodied carbon come from in glass manufacturing? It’s heat,” says Chris Fronsoe, national architectural team manager, Vitro Architectural Glass. “It’s where raw material goes up to about 3,000 degrees Fahrenheit and gets melted down into liquid material, and later in the float process goes back to solid.” For the manufacture of an insulating glass unit, roughly 75% of embodied carbon is generated during the manufacture of the raw glass lites in the float process due to the energy-intensive nature of the traditional float manufacturing process, says Fronsoe.

Several glass manufacturers have begun to change their processes to lower emissions in manufacturing. Increasing the use of cullet (crushed glass recycled back into the supply chain) in the process reduces the heat required to melt the materials in the furnaces, says Fronsoe. Additionally, a few glass manufacturers, such as Vitro, are using oxy-fuel technology in production, which can reduce energy consumption in glass-melting furnaces by as much as 20% and cut greenhouse gas emissions in half, he says.

Improve Operational Carbon

Operational carbon, on the other hand, refers to the emissions produced during a building’s lifespan. The glass industry has made “tremendous progress” in meeting increasingly stringent energy-efficiency requirements in the building codes, says Tom Culp, energy code consultant for the National Glass Association and owner of Birch Point Consulting. “In the 20-plus years I’ve been working in energy codes, [the industry] has cut energy use of buildings built to [the ASHRAE 90.1 Standard] by half.”

In terms of thermal performance, the industry offers dual, triple, and even quad IGUs. Fabricators have begun using two low-emissivity coatings in the IGUs for increased performance. And the industry continues to invest in next-generation thermal performance solutions, such as vacuum insulating glass and thin-triple IGUs, which provide even better efficiency within a narrow profile.

The glass industry also offers solutions to manage solar heat gain, which impacts building operational carbon. Tinted glass and switchable glass products, such as electrochromics, can further improve operational carbon.

Finally, using renewables will be essential in helping buildings become carbon-neutral, or net-zero. Rooftop solar or building-integrated photovoltaics, or BIPV, will help push operational carbon emissions even further. “Efficiency is one half of it, renewables are another,” says Culp.

Increase Recycling and Reuse

Lisa Rammig, director, Eckersley O’Callaghan, offered insights on how the industry could “reshape the future of glass” through an increase in flat glass recycling and an emphasis on rebuilding facades on existing structures. Only 6% of flat glass is recycled, according to 2017 estimates from Deloitte. If it is recycled, it is typically downcycled to glass bottles, insulation, or road filler. “Glass is a material that is fully and eternally recyclable, so why do we recycle so little flat glass? We need to change the status quo [of glass recycling],” says Rammig.

Additionally, Rammig encourages refurbishment—bringing new life into existing buildings—rather than constantly building new ones. “Don’t build. Reuse,” she says. “We should think about how we should extend the lifetimes of the buildings we have.”

Sophie Pennetier, associate director, special projects at Enclos, agrees. New buildings should also be “designed for disassembly,” she says. This means there will be easier recovery of products and materials when a building is disassembled or renovated, meaning less construction, and thus less carbon, will be produced.

Codes and Standards Drive Performance

Photo courtesy of Michael David Rose Photography

Lick-Wilmerding High School in San Francisco specified Low-E glass to introduce more transparency and daylight. In 2022, the school earned an AIA COTE Top Ten Award for sustainable design excellence.

The market is seeing new codes and standards that will require the use of better glass products. New legislation is providing major incentives for numerous types of improved glass and glass-related technologies. Below are the codes, standards, laws and regulations that are pushing for better-performing glass, glazing and fenestration, particularly: Energy Star 7.0, ASHRAE 90.1, the International Energy Conservation Code and some local city and state stretch codes.

Energy Star 7.0

The recently implemented Energy Star version 7.0 greatly increases thermal performance requirements for residential windows. Meeting the more stringent performance thresholds in the Northern climate zone, which covers about 40% of the U.S., will require the most advanced double-glazed IGUs or, more likely, triple- or quad-glazed IGUs, says Selkowitz. “We will need about 10 to 20 million triple-glazing units per year.”

ASHRAE 90.1

The most recently published version of building energy standard ASHRAE 90.1 2022 includes new on-site renewable energy requirements, thermal bridging requirements and additional energy credit requirements, including credit for higher-performance fenestration, shading, daylighting, rooftop solar panels and BIPV, says Culp. The new version of the code “takes a significant step in energy efficiency, and they are on target to hit net-zero by 2031, over the next three cycles,” Culp says. “The codes are moving faster than they ever have before.”

Work is ongoing in development for the 2025 version, which includes changes to the climate zone map. According to Culp, 9% of counties move to warmer climate zones and 3% move to cooler climate zones.

For fenestration, a proposal is under review to comprehensively update the U-factor and solar heat gain coefficient requirements for curtain walls, windows, skylights, and sloped glazing. This will provide the next incremental step in performance and continue to increase the use of fourth-surface low-e coatings, warm-edge spacers, inert gas fill, advanced thermal breaks and triple glazing. Additional proposals will expand credits for products such as dynamic glazing and automated shading, and increase the requirements for on-site renewable energy systems.

IECC

The International Energy Conservation Code “is also working towards net-zero goals, and the new 2024 version takes the first step,” says Culp. Notable updates, per Culp:

• No changes in window area limits.
• Marginal improvements in commercial and residential fenestration U-factor. For example, zone 4-5 went from 0.36 to 0.34, and zone 3 went from 0.42 to 0.38. No changes in SHGC.
• Credit for high-performance windows, increased daylight area, automated shading, PV, and BIPV.
• New requirements for on-site renewable energy (PV, BIPV) with off-site options if it can’t be done on-site.