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What is Embodied Carbon?

What is Embodied Carbon?

Posted: August 25, 2023 | Project Management

Understanding Embodied Carbon

As architects and glaziers work to design and construct building projects in a more sustainable manner, the consideration of embodied carbon has become a bigger factor in understanding the overall impact of a project’s carbon footprint.

Designers are working to balance the reduction of emissions from a building’s operations, known as operational carbon, with emissions caused by the manufacturing and installation of construction materials, known as embodied carbon.

Sustainability advocates are working to introduce initiatives such as the Buy Clean California Act (BCCA), which aims at reducing carbon emissions associated with the production of architectural products, and New York Local Law 97, which places carbon caps on large buildings. In August 2023, the California Building Standards Commission (CBSC) voted to approve two new building codes designed to limit embodied carbon emissions in both commercial and school projects over certain sizes, and experts predict similar legislation will pass in additional states in the years to come. To understand the impact these initiatives will have on the architectural glass industry, it is important to first understand the role embodied carbon plays in glass production.

Carbon and Architectural Glass Production

An important metric to consider that relates to embodied carbon in glass (or any building product) is Global Warming Potential (GWP). This measure takes all the energy used to create a product and converts it into kilograms of equivalent carbon dioxide, expressed as the term “CO2-eq.” The purpose of calculating GWP is to help stakeholders and sustainability programs more effectively gauge the environmental performance of glass and other products manufactured for buildings.

Most of the embodied carbon in glass originates with the energy-intensive process of heating the melting furnace to 3,000 degrees Fahrenheit to convert raw materials to flat glass. The processes of adding energy-efficient low-e coatings, tempering, laminating, and fabricating flat glass into insulating glass units (IGUs) also contribute to the glass’s GWP — but to a lesser degree.

In fact, approximately 78% of the embodied carbon in an IGU can be credited to the manufacturing of flat glass lites. It is estimated that of an IGU’s remaining embodied carbon, 13% comes from heat strengthening or tempering the glass, 10% comes from the IGU fabrication process itself, and just 2% comes from the process of adding low-e coatings.

Reducing Embodied Carbon

To reduce embodied carbon in architectural IGUs, glass manufacturers may consider taking some of the following steps to reduce overall energy consumption in glass production:

• Improving efficiency within furnace control systems to reduce variability of melting temperatures and fuel consumption
• Adding low-NOx burners to plants
• Using variable frequency drives on cooling fans to reduce energy use
• Utilizing recycled raw materials (both pre- and postindustrial) to reduce fuel consumption
• Converting facility lighting to LED, which reduces electric consumption by as much as 80% vs. incandescent lighting
• Using oxy-fuel technology, which can reduce energy consumption in glass melting furnaces by as much as 20% and cut greenhouse gas emissions in half

It also is important to note the return on carbon that energyefficient glazings deliver. While the production of raw glass does carry embedded carbon, high-performing low-e coated glass reduces the negative environmental impact on the built environment.

Evaluating Embodied Carbon

Environmental Products Declarations (EPDs) are thirdparty verified documents that provide detailed data about the life cycle impacts of building products on the environment and may be used as credentialing for LEED® and other green building certification programs.

It is important to understand how to properly read, interpret and utilize data that is published in EPDs, which should generally be used to inform and indicate compliance with the requirements of green building rating systems and legislative actions. The purpose of an EPD is to provide information on the environmental impact of the product over its life cycle, and they typically rely on estimations of impacts and can therefore differ across product lines and reported impact. In the context of evaluating embodied carbon, EPDs likely will offer the most value in interpreting how a given product was manufactured and what steps manufacturers are taking to reduce energy expenditures.

Each material is evaluated based upon Product Category Rule (PCR) as determined by ASTM, on how to conduct a Life Cycle Assessment (LCA). For flat glass, the declared unit for a LCA 1 metric ton of glass, maintained for a 30-year period, as specified by the Glass Association of North America (GANA) PCR for Flat Glass. For processed glass, the declared unit is m2, as specified by the UL Environment PCR Guidance for Building-Related Products and Services: Part B: Processed Glass EPD Requirements.

In the U.S., a product’s life cycle is from cradle to gate, whereas in Europe, it’s cradle to grave. If architects are interested in the breakdown of materials used to create the glass, this is listed in the EPD. For an IGU, for example, it’s important to note that the vast percentage of embodied carbon is in the glass itself, with a low percentage in the spacer materials. Consequently, the biggest environmental impact comes from the glass.

Another evaluation tool is the EC3 tool. Envisioned by the non-profit Building Transparency, this calculator is being created to help architects and other stakeholders benchmark, assess and reduce the amount of embodied carbon used among all the building products (including glass) specified for their construction projects.

Health Product Declarations (HPDs) are an additional way manufacturers can provide transparency about the environmental impacts of their products and manufacturing processes. An HPD is a self-evaluation declaring that a manufacturer is not using hazardous materials in the manufacturing and production of their glass. Furthermore, manufacturers are distinguishing themselves as sustainability leaders by achieving the Cradle to Cradle Certified™ Product Standard, which evaluates and certifies the formulation and production of products based upon Material Health, Material Reutilization, Renewable Energy & Carbon Management, Water Stewardship and Social Fairness.

Ultimately, architects and building owners are very interested in boosting sustainability and energy efficiency and driving down embodied carbon. One of the best ways to know exactly how much a given product will impact the environment is through the data in an EPD, specifically the GWP.

For more information about EPDs for glass industry products, review the National Glass Association’s General EPD Education document, available on the NGA website at

To download Vitro’s Uncoated Glass and Processed Glass EPDs, visit