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Embodied carbon vs. operational carbon. Life cycle assessment vs. hot spot assessment. EPD, GWP, RCA… We gathered all the terms and acronyms used when working to reduce embodied carbon emissions from construction projects.
Embodied carbon (spoiler: it’s the emissions associated with building materials and products) is becoming a bigger part of the conversation about net zero buildings. But the terms associated with embodied carbon are still relatively new and mean different things to different people. Often, these terms don’t have industry-standard definitions (yet).
Our sustainability consultants at SWA created this glossary to help establish standard definitions for key terms based on our extensive work with project teams to reduce carbon emissions from buildings.
We want this to be a living resource—we’ll continue to add terms that practitioners need to know.
Any gas—both human-created and natural—that absorbs and re-radiates infrared radiation effectively trapping heat and contributing to the greenhouse effect, which raises the Earth’s temperature.
A greenhouse gas that traps heat and contributes to global warming. It comes from the burning of fossil fuels, wildfires, volcanic eruptions, and other environmental sources.
A unit of measurement that compares the climate impact of different greenhouse gases (GHGs). The unit defines how companies can measure the carbon footprint of their products.
The emissions associated with energy used to operate a building or in the operation of infrastructure, including heating, hot water, cooling, ventilation, lighting systems, equipment, and lifts.
The greenhouse gas (GHG) emissions associated with the manufacturing, transportation, installation, maintenance, and disposal of building materials and products over the entire life cycle of a building, not including the operations or use phase.
All energy used by the building must be clean energy, obtained through any combination of on- and off-site sources, as long as the GHG emissions from that clean energy equal zero. If the building obtains heating or cooling from a district energy system, the district energy must be generated from clean sources.
The two main ways to reduce embodied carbon are to use fewer materials and choose materials with lower carbon footprints. For example, using regional materials with recycled content like ground glass in concrete mixes and using less material by optimizing the sizing of structural components (click to see definitions below). During construction, reduce carbon impacts by using low-emission vehicles and equipment.
The concept that reducing carbon emissions today is significantly more valuable than reducing the same amount of emissions in the future, because the longer we wait to act, the greater the cumulative climate-change impacts will be.
The time it takes for an energy cost measure to recoup the cost of that measure through energy savings. It is calculated by dividing the total cost of the investment by the annual energy savings.
All stages from conception to demolition and disposal. This includes all aspects of the building, from its components and systems to its building services.
The total carbon emissions produced by a building throughout its life cycle, from material extraction through construction to demolition and disposal including operational emissions.
An embodied carbon assessment in the schematic design phase or earlier informs the design by:
An assessment of environmental impacts, including embodied carbon, after the initial hot spot assessment. This analysis includes a compilation and evaluation of the inputs, outputs, and potential environmental impacts of a product or system throughout its life cycle, including global warming potential (GWP), ozone depletion, and other impacts to systems fundamental to life on earth.
The point at which a material or system degrades through age or wear to significantly reduced effectiveness. Commonly determined as when material or system replacement is needed.
The process of repurposing an existing building for a new use. Reuse can avoid significant carbon emissions from not using as much new material, particularly in the structure.
A common reporting document showing the emission results for a product or material LCA throughout its lifecycle.
ISO 14025:2006 established principles and procedures for developing product specific EPDs. These allow some comparability between materials and products. Other types of EPDs report industry-wide averages and are not product specific.
It is important to use EPDs within the context of a whole-building life cycle assessment, where their data can be harmonized and applied consistently across all materials, opposed to comparing EPDs side by side.
The metric used to measure and track embodied carbon expressed in units of kilograms of CO2 equivalent (kg CO2e). The “equivalent” or “e” means that other greenhouse gases like methane—which are far more potent GHG emitters than CO2—are accounted for in terms of their equivalent impact. For instance, the same mass of methane will trap significantly more heat in the atmosphere than CO2 over the specified timeframes.
A material, product, or equipment that has significantly lower GWP emissions during its lifespan when compared to the average equivalent material, product, or equipment. Note, that “Low-GWP” does not have an empirical definition; all claims of “low-GWP” should be reviewed for accuracy by comparing to other materials, products, or equipment in the same category and by examining the source of the claim.
Biobased products that are derived from renewable biological resources like plants, animals, fungi, and microbes. They can be used in many industries, including construction, personal care, and packaging. Biobased products can be an alternative to petroleum-derived products, and they can help reduce carbon impacts. Examples are cellulose, wood fiber, cotton, or hemp-based materials.
There are two main certifications for wood, the Forest Stewardship Council (FSC) and the Sustainable Forestry Initiative (SFI). Both promote sustainably managed forests and sustainably grown wood can be aa lower-carbon option for structural use than steel or concrete. Certified wood products ensure the wood use in buildings does not contribute to deforestation and other impacts such as forced labor.
FSC focuses on a global, ecologically driven approach to forest management, while SFI emphasizes sustainable practices within North America. Both include a comprehensive chain-of-custody system.
Material that has been diverted from a waste stream and reprocessed into a new product. Types of recycled material:
Misleading the public to believe that a company or other product is doing more to protect the environment than it is. Greenwashing promotes false solutions to the climate crisis that distract from and delay concrete and credible action.
Some things to look out for are public claims about a specific material being the lowest carbon option or claims of carbon absorbing or sequestering potential. Be sure to evaluate claims using a whole-building life cycle analysis and not simply comparing EPDs side by side. Comparing EPDs is tricky because they do not always include the same life cycle stages or may not be independently verified. ISO 21930 provides specific guidelines for comparing EPDs for construction products.
Carbon sequestration occurs when a material either stores or captures atmospheric carbon dioxide (CO₂). For example, concrete surfaces slowly absorb some CO2 in a process called carbonation, whereas growing trees and other organisms store carbon.
Materials used in combination with Portland cement to enhance the properties of concrete. These materials can improve the strength, durability, and sustainability of concrete through hydraulic or pozzolanic activity. Examples of these materials are post-industrial waste products like ground granulated blast-furnace slag (GGBFS) from steel mills, fly ash from coal plant stacks, and recycled pozzolans like ground glass from post-consumer recycling programs. SCMs are very common in the industry and widely used.
Concrete from demolished structures can be reused in many ways including for roadways and as an ingredient in new concrete.
Contributors: Kai Starn, Senior Sustainability Consultant; Zachary Vergata, Sustainability Specialist; Lois Arena, Director, High Performance Building Solutions
