Glass and Embodied Carbon

Sustainable design and construction continue to grow in importance in today’s building projects. Driven by stricter building codes and standards, green building certifications, climate change concerns, strong tenant preferences and an increased focus on embodied carbon, architects and building owners are tasked with lowering their energy use levels and procuring low-carbon materials.

To best navigate this evolving landscape of carbon assessments, expectations and requirements, it’s helpful to better understand carbon, how to measure it, how to reduce it in glass manufacturing and how the latest building codes and standards are driving the specification of lower carbon products and materials.

Defining Carbon

Carbon dioxide (CO₂) is the primary contributor to greenhouse gas emissions and global warming. With the built environment comprising approximately 40% of annual CO₂ emissions, the building industry is stepping up, initiating programs, policies, technology and product developments to help curb emissions.

The carbon associated with buildings is broken down into two categories: operational carbon and embodied carbon. Operational carbon is the amount of energy required to light, heat, cool, ventilate and control buildings and is spread out over a building’s lifetime.

Embodied carbon is the amount of carbon associated with the construction of a building. This includes all the carbon extracted to manufacture the materials, products and systems that go into the building, transporting these materials, and the construction process.

While embodied carbon comprises approximately one third of all the carbon associated with buildings, the benefits of reductions in this “up front” carbon can be captured in the short term whereas operational carbon reductions take time to add up over the lifetime of the building.

Carbon and Glass

With regards to operational carbon, low-e, solar control glazings can significantly reduce electrical lighting consumption and HVAC energy use. This enhances energy efficiency, lowers energy bills and reduces carbon emissions.

Concretizing the energy saving values provided by glazing, Vitro Architectural Glass offers an emissions calculator to compute energy savings based on the building type, location and orientation, glass type, window-to-wall ratio and more. The calculator then breaks down all the operational values.

For embodied carbon, the most comprehensive metric for measuring Green House Gas (GHG) emissions is Global Warming Potential (GWP). This value takes all the energy used to create a product and converts it into kilograms of equivalent carbon dioxide, expressed as the term “CO₂-eq.”

A product’s calculated GWP serves as the key metric for evaluating the environmental impact of manufactured products including glass.

Glass Production and GWP

The vast majority, approximately 78% of the carbon, is in the uncoated flat glass. This is created by the energy-intensive process of melting silica, soda ash, dolomite, metal compounds and recycled cullet glass at 3,000 degrees Fahrenheit to manufacture the glass.

Of the remaining embodied carbon, approximately 12% is created by the insulating glass unit (IGU) fabrication process and 10% comes from the heat treatment process and adding energy-efficient low-e coatings.

Given these percentages, Vitro recommends using a Flat Glass Environmental Product Declaration (EPD) to evaluate carbon content since the majority of GWP for processed glass IGUs comes from flat glass. Building industry professionals then reference the GWP value contained within the EPD produced by building industry groups and individual manufacturers.

PCRs and EPDs

Third-party verified, EPDs are developed based upon Product Category Rules (PCRs), per American Society for Testing and Materials (ASTM), on how to conduct a life-cycle assessment (LCA). The EPD transparently reports all the environmental impacts in an LCA from raw material extraction to the final product.

The declared unit for flat glass in LCA data is one metric ton (1000 kg) of float glass maintained for 30 years. For processed glass, the declared unit is square meters (m²),

While EPDs are a valuable tool for architects evaluating the sustainable attributes of different glass products, comparing glass to other materials is not recommended.

For starters, different materials use different product category rules. Furthermore, there can be variations in the methodology, assumptions, allocation methods, data quality and assessment software tools used to compute environmental impact levels.

Even comparing North American glass manufacturers with European glass manufacturers is not so straightforward as they don’t use the same PCR, plus North America utilizes a cradle-to-gate LCA and in Europe, the LCA is cradle to grave.

An EPD should be product-specific vs. industry wide. In addition, Vitro recommends general EPDs vs. facility plant-specific EPDs. Generally speaking, not all products are made at all plants. Consequently, facility-specific EPDs can be misleading.

Consistency and Quality of Embodied Carbon Data

Back in 2017, Vitro became the first North American manufacturer to publish third-party verified EPDs for flat glass and processed glass products.

Then in 2019, the National Glass Association published an architectural glass EPD for clear, low-iron and tinted flat glass produced by four member companies of the NGA’s Forming Committee, including Vitro. Its findings suggested an industry average GWP of 1,430 kilograms for comparable products.

In 2024, Vitro updated its EPD for its flat glass products and reported an even lower GWP of just 1,240 kilograms of CO₂ equivalent. This is 13% lower than the NGA’s industry standard.

This lower GWP value places Vitro in the U.S. General Services Administration’s (GSA) top 20% "Most Preferred" low embodied carbon (LEC) material category.

For more information on the variety of strategies Vitro employed to drive down the embodied carbon in its glass manufacturing process, see “Embodied Carbon: Understanding Embodied Carbon in Glass.

Unlike many EPDs which are only based upon 12 months of data, Vitro provided 24 months of data for their latest third-party, verified EPD.

Another distinction is that with some exceptions, EPDs usually are not applicable to all manufacturer’s plants. However, in Vitro’s case, the EPD applies to all Vitro products and plants, all the time.

Code Development

As manufacturers work to bring down embodied carbon levels in their products, architects and building owners will increasingly be looking for those options to help comply with stricter building codes.

A Federal-State Buy Clean Partnership with 13 states seals a commitment to prioritize efforts that support the procurement of lower-carbon infrastructure materials in state-funded projects. So far, Washington, Oregon, Minnesota and Colorado have already signed related legislation into law, and other partnership states include California, Hawaii, Illinois, Maine, Maryland, Massachusetts, Michigan, New Jersey, and New York.

California and New York have also been aggressively pursuing carbon goals through the CalGreen Building Standards Code and Local Law 97.

Recent updates to CalGreen have raised the stakes on embodied carbon with stricter requirements applying to non-residential developments over 100,000 square feet and school constructions exceeding 50,000 square feet.

Meanwhile, New York’s Local Law 97 requires a reduction in greenhouse gas emissions of 40% by 2024, compared to 2005 levels, for a single building exceeding 25,000 gross square feet and two or more buildings on the same tax lot that together exceed 50,000 square feet.

Moving Forward

It’s an exciting time for the glass and building industry. Interest in sustainable design will continue to grow as will technologies, programs, regulations and codes.

It will be in architects’, owners’ and other stakeholders’ best interests to stay abreast of the latest changes and developments.

For a more extensive document, unpacking more details in all the above-mentioned topics, see Vitro’s Glass and Carbon white paper.