Greenhouse Gas Management of Embodied Carbon in Building Materials
Greenhouse Gas Management of Embodied Carbon in Building Materials
Embodied carbon consists of all the greenhouse gas emissions associated with building construction, including those that arise from extracting, transporting, manufacturing and installing building materials on-site, as well as the operational and end-of-life emissions associated with those materials.
“Cradle to gate” embodied carbon refers to the emissions associated with only the production of building materials, from raw material extraction to the manufacturing of finished products; it can be thought of as supply-chain carbon, and it accounts for most of a building’s total embodied carbon.
An obstacle to identifying and purchasing products with lower embodied carbon is a lack of data quality and the transparency of environmental product declarations (EPDs). However, EPDs vary widely in their data quality and specificity, which can lead to inaccurate and misleading comparisons. A new method is presented to account quantitatively for estimates of variation in underlying data specificity in EPDs to enable fairer comparisons between EPDs and to motivate the reporting of actual variability and uncertainty in EPDs. The application of this approach can help purchasers to assess EPDs quantitatively.
How to measure and report:
Unfortunately, embodied carbon is more difficult to measure and track than operational carbon, which is relatively simple to extrapolate from a health care organization’s energy bills. The embodied carbon of any building material is impossible to ascertain from the finished product alone, and instead requires self-assessment and process transparency on the part of the manufacturer. Two materials may look identical, cost the same amount, perform to the same standard — but have totally different embodied carbon characteristics. For example, a 100% recycled-steel beam produced using renewable energy may appear identical to a virgin-steel beam produced using a coal-fired furnace — but have significantly different levels of embodied carbon. Where each steel beam came from and how far it was transported add further complexity.
Life-cycle assessments (LCAs) and LCA data can be used within the construction sector to evaluate buildings and to assist in design, specification and procurement decision-making. A new method is presented to support the assessment of comparability of functionally equivalent materials and products during the specification and procurement stage. Given the known variation and lack of precision within EPDs, this method provides quantitative metrics that correlate to a qualitative interpretation of EPD precision. This method can be used by anyone who is using EPD data to make product comparisons at the specification and procurement stage.
How to manage:
Reuse buildings instead of constructing new ones. Renovation and reuse projects typically save between 50% and 75% of the embodied carbon emissions compared to constructing a new building. This is especially true if the foundations and structure are preserved, since most embodied carbon resides there. With many projects, the first question should be, "Is there an existing building we can use instead?" This is an admittedly hard sell for architects — after all, many architects got into the business for the excitement and challenge of designing something new from the ground up. But redirecting that energy and creativity away from designing poor-performing buildings and toward making into designing something beautiful, sustainable and energy efficient has its own rewards, and yields substantial positive benefits.
Specify low-carbon concrete mixes. Although its emissions per ton are relatively low, concrete’s weight and prevalence usually make it the biggest source of embodied carbon in virtually any project. The solution? Work with a structural engineers to design lower-carbon concrete mixes by using fly ash, slag, calcined clays or even lower-strength concrete where feasible. Though access to these materials varies based on location, there is an ever-increasing range of alternative options available that can reduce the carbon footprint of a concrete mix.
Limit carbon-intensive materials. For products with high carbon footprints like aluminum, plastics and foam insulation, thoughtful use is essential. For instance, while aluminum may complement the aesthetics of your project, it is still important to use it judiciously because of its significant carbon footprint.
Choose lower-carbon alternatives. Think about the possibilities. If a wood structure is a viable alternative to steel and concrete, or wood siding instead of vinyl, these substitutions can reduce the embodied carbon in a project. In most cases, it may not be possible to altogether avoid carbon intensive products like plastics or aluminum and other metals, but one can review environmental product declarations and seek lower-carbon alternatives.
Choose carbon-sequestering materials. Using agricultural products that sequester carbon can make a big impact on the embodied carbon in a project. Wood may first come to mind, but also consider options like straw or hemp insulation, which — unlike wood — are annually renewable.
Reuse materials. Whenever possible, look to salvage materials like brick, metals, broken concrete or wood. Salvaged materials typically have a much lower embodied carbon footprint than newly manufactured materials, since the carbon required to manufacture them has already been spent. Reclaimed wood, in particular, not only saves the energy that would have been spent cutting the tree down, transporting it to the mill and processing it, but a tree that was never cut down is still doing the work of sequestering carbon.
Use high-recycled content materials. This is especially important with metals and finishes such as carpet. Virgin steel, for example, can have an embodied carbon footprint that is five times greater than high-recycled content steel. Specifying a high recycled-content carpet can reduce embodied carbon of the building significantly.
Maximize structural efficiency. Because most of a building’s embodied carbon is in its structure, look for ways to achieve maximum structural efficiency. Applying optimum value engineering to wood framing methods, making efficient structural sections and using slabs are all effective methods to maximize efficiency and minimize material use.
Use fewer finish materials. One way to do this is to use structural materials as finish. Using polished concrete slabs as finished flooring saves the embodied carbon from carpet or vinyl flooring. Unfinished ceilings are another potential source of embodied carbon savings.
Minimize waste. Designing in modules, auditing your waste streams, and reviewing your processes to identify generation points are all strategies that can be implemented to minimize waste.
©2023 The American Society for Health Care Engineering (ASHE) of the American Hospital Association
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