Embodied Carbon

Embodied Carbon in Buildings and Building Materials

“Buildings are currently responsible for 39% of global energy related carbon emissions: 28% from operational emissions, from energy needed to heat, cool and power them, and the remaining 11% from materials and construction [also known as embodied carbon].

Towards the middle of the century, as the world’s population approaches 10 billion, the global building stock is expected to double in size. Carbon emissions released before the built asset is used, referred to as ‘upfront carbon’ [or ‘embodied carbon’], will be responsible for half of the entire carbon footprint of new construction between now and 2050, threatening to consume a large part of our remaining carbon budget.“

- World Green Building Council

Getting Started

Embodied carbon refers to the carbon emissions released during the extraction, manufacturing, transportation, construction and end-of-life phases of buildings; it accounts for around 11 percent of all global carbon emissions. Embodied carbon may refer to the embodied carbon of a whole building or the embodied carbon of a single building material.  Often referred to as the hidden carbon impact of the buildings and construction sector, embodied carbon’s impact on global carbon emissions presents a significant opportunity for jurisdictions to drastically and quickly curb global carbon emissions by adopting policies that address embodied carbon. Additionally, the World Green Building Council theorizes that “if the building and construction sector were to drastically shift demand towards low carbon options for [the most carbon intensive materials: concrete, steel and aluminum], this would require a transformation in the manufacturing processes of the supply chain. This would affect the total emissions for those materials streams and have an enormous impact on emissions mostly attributed to other sectors through these three materials alone. The total potential impact, therefore, of the buildings and construction sector, is far greater.”

Unlike operational carbon emissions, which can be reduced over time with building energy efficiency renovations and the use of renewable energy, embodied carbon emissions are comprised of (1) one-time emissions from construction material extraction, manufacturing, and transportation; and (2) the one-time emissions from the construction of a building, and they cannot be taken back once emitted.

The building sector is well-positioned to have a significant impact on emissions reductions, given the impact of embodied carbon on global carbon emissions, and the limited attention that these sources of emissions have had to date. Building design teams that seek to minimize both operational and embodied carbon emissions can significantly reduce their overall carbon footprint, low carbon alternatives exist today. Predominant building materials like concrete, steel, wood, and insulation have high-impact potential for emissions reductions, and in some cases, there are opportunities for carbon sequestration in these and other materials. Secondly, consideration of lower emission products challenges many existing building practices and industrial norms. Not unlike the early years of green building, the subject of embodied carbon in the built environment is relatively new, and dynamic, and there is not yet industry consensus.

Operational Carbon versus Embodied Carbon

Evolution of the energy codes over the last three decades has offered a significant decrease in operational carbon emissions. Only recently has more information become available to help builders and designers make decisions regarding reducing embodied carbon. Unlike operational carbon emissions which can be reduced over time with building energy efficiency retrofits, future electrification of HVAC and the addition of renewable energy, embodied carbon emissions are locked in place once the building is built.

Including embodied carbon in the suite of policies, building codes and design choices is another tool for jurisdictions to address climate impact of the built environment.

 The American Institute of Architects has identified 10 steps that can be taken to reduce embodied carbon.

  1. Reuse buildings instead of constructing new ones.
  2. Use low carbon concrete mixes.
  3. Limit carbon intensive materials.
  4. Choose lower carbon alternatives.
  5. Choose carbon sequestering materials.
  6. Reuse materials.
  7. Use high-recycled content materials.
  8. Maximize structural efficiency.
  9. Use fewer finish materials.
  10. Minimize waste.

LEED, the International Green Construction Code, and Living Future are helping to build market awareness of these material choices and create a market for beneficial products. In addition,  jurisdictions can have a significant impact through incorporating embodied carbon policies into and alongside codes and standards.

“Building elements such as foundations, frames and other forms of superstructure often represent the biggest contribution to embodied carbon, not least because of the large volumes of material they use. But, additionally, these elements often contain carbon intensive load bearing structural materials such as steel, concrete and masonry. Facades may also contribute significantly if they utilize large amounts of aluminium and glass, both of which have carbon intensive production processes.”

  • Concrete is the most widely used construction material throughout the world and it’s responsible for 6-11% of global CO2 emissions. Using less cement in the concrete mix, whilst maintaining its structural integrity, is the most effective way to reduce the carbon footprint of concrete. Design teams can also be incentivized to use less concrete in many structures.
  • For steel, the embodied carbon impact can differ based on the manufacturing process used. Most of the current global steel production is manufactured using a basic oxygen furnace (BOFs) production method. Under this method 37% of materials are recycled content. Whereas as electric arc furnaces (EAFs) can use up to 100% recycled material without compromising metallurgical properties. Furthermore, since EAFs are powered by electricity there is potential for this manufacturing process to further reduce emissions when powered by renewable energy.
  • Wood naturally sequesters carbon while growing and will continue to store carbon when used in construction. Using reclaimed wood and specifying use of wood from sustainably managed forests is the best way to reduce embodied carbon emissions from wood harvesting. Where sustainably harvested wood is used as a structural alternative to steel or other more emissions intensive products it reduces embodied carbon. This has led to growing interest in mass timber framed buildings and structural products such as cross-laminated timber, that have significant potential economic and emissions benefits over more traditional steel-framed commercial buildings.
  • Insulation can contribute significantly to a building’s embodied carbon or alternatively help to sequester carbon depending on the materials used. When selecting insulation, thermal operational energy considerations should be balanced with an awareness of embodied carbon impacts and targets.

This is just a subset of building materials that have low-carbon alternatives. The current challenge is accurately quantifying the impact of reducing embodied carbon. However, this will only become easier as awareness grows throughout the industry and more industry practitioners decide to focus on the embodied carbon impact of their buildings.

Determining the Embodied Carbon of Building Materials and Products

Accurately quantifying the embodied carbon or CO2 equivalent emissions associated with a building material’s “cradle to grave” footprint is challenging, but becoming increasingly more accessible and affordable. Three tools are used to determine the embodied carbon: the Product Category Rule (PCR), Life Cycle Assessment (LCA), and Environmental Product Declaration (EPD).  

Product Category Rule.  The PCR sets up the rules or criteria by which a specific building material or product type is evaluated regarding its environmental impacts.  These criteria may include things like the market location, or rules for averaging. The lack of standardized methodology in developing PCRs has resulted in incomparable environmental claims  and has reduced the overall credibility of the LCA-based product claims for decision making.

Life Cycle Assessment. Once a PCR has been developed an LCA is performed and a report of the results is produced.   An LCA is a science-based holistic methodology that seeks to answer the question of “how sustainable is a product, building, or process?” so that a project team may identify the “environmental hotspots” of a building with respect to greenhouse gas emissions and environmental impact, and make informed design decisions that minimize the environmental impact of the building.   An LCA seeks to provide transparency about the environmental impact of a building project over its lifetime from the extraction of materials for manufacturing, to transportation, construction, operations, and building’s end-of-life. The process of performing an LCA involves a lot of data gathering, computer modeling and documentation.   The software used to model the results pulls raw material data from one of a few existing databases.  It should be noted that there are differences in the databases and software that will produce different results for the same product.  LCAs are  detailed and often contain proprietary product formulation or manufacturing information; they are rarely released publicly.

Environment Product Declaration. The EPD is provided by a product manufacturer or industry.  A third-party will take the LCA and summarize the important information in the EPD.  Depending on how the LCA was conducted, an EPD may provide averaged industry wide information, averaged product family information, or specific product information. EPD development is standardized by ISO 14025, Environmental Labels and Declarations, Type III Environmental Declarations, Principles and Procedures. Before an EPD can be produced, a Product Category Rule (PCR) needs to be created. EPDs do not include this proprietary information and are typically available on public websites.

Comparisons of EPD data, like carbon dioxide (CO2) emissions are only reliable when they have used the same PCR and LCA software and assumptions.  Changes in versions of software and PCRs can have a significant impact on the results. Evaluating both the embodied and operational carbon impacts of a building project should be viewed as a holistic process. There may be times when project goals conflict with one another and compromises will need to be made. For instance, there are a variety of other criteria that must also be considered during project development such as durability, fire safety, structural safety and moisture management.  It is imperative that policy makers and users understand the limitations of available data.

Embodied Carbon Policy Case Study: City of Vancouver, British Columbia

“Vancouver has a goal to achieve a 40% reduction in embodied carbon from construction by 2030 [compared to 2018 levels]. As part of this strategy, the City of Vancouver will use its policy and regulation, public procurement, networks and influence to create a more sustainable way of building in the city. With a concerted effort, the City can transform how buildings are built, what they are made of, and the impacts of those materials before, during, and after a building is used. Carbon pollution can be significantly reduced while also improving health, equity and waste outcomes from construction and its materials.”

The city has adopted four actions, each with the goal of transforming different parts of the construction sector to achieve the goal.  The four actions are summarized as follows.  Detail can be found in Appendix K of the Vancouver Climate Emergency Action Plan[2].

  • Change the Rules: Policy and Regulation “It’s only permitted to build low-carbon buildings” (section 4.1)
  • Change the Market: Remove Barriers and Provide Incentives “It pays to build low-carbon buildings” (section 4.2)
  • Change the Culture: Capacity Building and Industry Transformation “Our knowledge, tools, networks, and culture support low-carbon buildings” (section 4.3)
  • Change the Context: Complimentary Strategies and Actions “The construction ecosystem enables and encourages low-carbon buildings” (Section 4.4)

Resources

There are several resources and tools available to help guide users when making decisions about building materials and products.  When using these tools and resources, it is highly recommended that the user become familiar with the methodologies used to develop them and be mindful that the information contained in some tools may not be comparable to another tool. Visit the International Code Council energy resources page for more information.

Distributed Energy Resources

Distributed Energy Resources

Clean-energy, including on-site renewables, energy storage and energy-efficient technologies, such as electric vehicles, separately and together are increasingly being adopted to support energy efficiency and decarbonization goals.  As these technologies become more prevalent on the customer side of the meter, the energy distribution system must evolve to account for them in the supply and demand equation. Integration of these technologies into the electrical grid is critical to ensure that utilities can continue to operate the grid in a safe, reliable and cost-effective manner. View the topics below, and visit the model policy and resource page for more information.

Getting Started

Distributed Energy Resources (DER) complement regional power plant and fossil fuel distribution systems by providing local points where electricity is generated, waste heat is recaptured and/or excess energy is stored for later use. DER or virtual power plants can interact productively with the regional electrical grid by reducing overall loads and shifting loads from peak to off-peak hours. This allows regional generating systems to reduce fossil fuel consumption and carbon emissions, especially when compared to carbon-intensive, highly-polluting peaker plants.

Standby diesel generators, microturbines and other electric generation technologies with lower efficiency and higher emissions than central station power plants can be classified as DER. For the purposes of this document, however, and in the interest of reducing carbon emissions, the focus is placed on DER derived from renewable sources. DER can contribute to the resiliency and reliability of the grid by providing local generation and storage that could be deployed and utilized during failures in portions of the distribution line. Communities with lower system stability and reliability can particularly benefit from the deployment of robust DER systems in key priority locations.

During a two-month period in 2020, communities in Louisiana experienced three hurricanes resulting in a loss of power for over one million people and 73 inoperable sewage stations. Restoring power took weeks. Even short-term power outages can have serious health implications for medically vulnerable persons who rely on electric medical equipment. Recommendations to improve the reliability of the grid included investment in virtual power plants, incentivizing solar+storage in community facilities that function as shelters, and providing equity to environmental justice communities.

DER technology is relatively new and rapidly evolving. Policies aiming to encourage the use of DER technology should be flexible enough to account for innovation. Policies should also be performance-driven, emphasizing goals for carbon reduction and energy efficiency over prescriptive language or strict adherence to specific technologies.

Demand-responsiveness typically requires an agreement between a building owner and the local utility but can also be set up independently by a building owner as a means of reducing power usage, and thus high electrical rates, during peak hours.

A modernized grid that is resilient, reliable and flexible is based on two key elements: front-of-the-meter and behind-the-meter components. The front-of-the-meter component involves the integration of DER into the utility power grid. The behind-the-meter component requires building-to-grid integration in the form of an information loop between buildings and the grid that, at a minimum, tracks patterns of energy production (if any) and consumption.  Buildings account for 75 percent of electricity consumption in the US;[ii] a policy that does not include building performance or building-grid interaction has limited potential to reach energy-efficiency goals.

Multiple fundamental decisions must be made as building-to-grid integration policies are developed. Before consideration of renewable energy or other demand response strategies, a foundational step should be a careful analysis to determine whether all available passive design strategies  and energy efficiency measures have been optimized. Some considerations are listed below as a starting point for DER policy development.

DER policies might be documented in or integrated with codes such as:

  • Building Codes
  • Electrical Codes
  • Fire Codes
  • Energy Conservation Codes
  • Land Use Codes

The policies might be applicable to:

  • New construction projects
  • Major alterations
  • Existing buildings

Within each of those project categories, policies may be applied to building types:

  • Single-family
  • Multifamily
  • Commercial
  • Industrial

Policies may also be implemented for building of a given size:

  • All buildings
  • Buildings over 2,500 square feet
  • Buildings over 20,000 square feet

The minimum required capacity of on-site or off-site zero-carbon energy systems could be based on:

  • Typical energy use intensity for the building type (schools and office buildings may require less, while hospitals may require more. Utility bill records could provide use data.)
  • Available roof area
  • Building floor area

Decisions must be made regarding whether DER policies will include sector-specific targets such as DER deployment in the transportation, industrial, commercial and residential sectors. Where investments and incentives are being proposed for the use of DER technologies, policies may also set targets for a portion of the sources being directed to those specific sectors and/or to disadvantaged communities, consistent with the municipality’s environmental justice goals. Decisions must also be made regarding whether “EV ready,” “renewable ready” (wind, solar, geothermal, biomass, etc.) or “demand response readiness” should be required for new construction, to facilitate future installation or expansion of such systems.

Scalable DER Power Technologies

Scalable technologies include both on-site generation resources and off-site renewable alternatives.

Solar photovoltaic (PV) arrays are the most common form of distributed renewable energy. Costs for PV systems have fallen drastically over the years, and continue to fall, while their efficiency at converting incoming solar rays to electricity improves. PV installation is most feasible and cost-effective when coordinated with new construction. When installation during construction is not an option, the next best choice is solar readiness (Appendices CB and RB of the 2021 IECC). Given the right solar orientation, systems are commonly installed on existing roofs or on-ground where land is available.

Solar thermal arrays for generating hot water are another possibility for on-site renewables. Once the on-site storage tanks are sufficiently heated, however, there is generally no further productive use for the excess solar energy, as opposed to PV arrays which can either store on-site or export excess electricity out to the grid. While the technology of the systems is relatively simple and time-tested, the system’s pumps, exterior piping and controls require ongoing maintenance. The cost of long-term maintenance needs to be considered in the pay-back analysis.

Building-mounted wind turbine generators are available in several varieties. Their suitability for a particular site and a payback that includes maintenance need to be carefully evaluated.

Ground source heat pumps transfer heat from one area to another and capitalize on the relatively constant temperatures a few feet below the earth’s surface to capture heat during the winter and to dissipate heat during the summer. Air source heat pumps perform a similar function and are less expensive, but their efficiency is 25 to 50 percent lower than that of ground source heat pumps. One alternative to achieve higher efficiency and lower cost is a dual-source heat pump.

On-site energy generation goals can also be coupled with a jurisdiction’s environmental justice goals. The Energy Trust of Oregon was one of the recipients of the 2020 State Leadership in Clean Energy Awards for their Inclusive Innovation Project. The project makes solar energy generation affordable and accessible to low income, rural, and traditionally under-served communities.

Where a building and its site lack sufficient wind, solar exposure or space for the installation of on-site renewables, as is the case with some slender buildings or buildings with heavy process loads, some off-site source of renewable energy might be desired or required by local policies or regulations. The ownership and billing credit for off-site generation requires the cooperation of a local utility. The purchase of renewable energy certificates (RECs) is another alternative, but it can be challenging as it is often unclear whether such purchases result directly in the construction of new renewable energy resources, and how far into the future that renewable energy benefit might extend. Community solar programs provide an attractive option in those areas where such programs are available. At the utility level, offshore wind generation is an alternative for coastal states. Large scale offshore wind projects have been implemented in New York State as part of the state’s clean energy and public health goals.

EV Infrastructure 

EVs have an important role to play in strategies for decarbonization and reduction of harmful emissions. One of the barriers to successfully reaching EV goals is range anxiety, or the fear that an EV will have insufficient charge to reach a charging station. At the larger scale, infrastructure investment and incentives can be implemented to provide charging stations at existing service stations, parking lots and along public ways. At the building scale, EV charging at buildings and building sites can be required as part of decarbonization and energy-efficient policies; cities such as New York City already do so. Since the 2016 version, the California Green Building Standard (CALGreen), has required EV readiness for residential and commercial buildings as part of the state’s Zero-emission Vehicles Action Plan. Vehicle batteries provide one convenient option for storage and use of excess renewable energy generation, either directly to plugged-in vehicles or indirectly into dedicated energy storage. This avoids the losses that occur with DC to AC power conversion.

Energy Storage 

By large, the most accessible forms of renewable energy are intermittent by nature because solar energy is only available during daylight hours and wind speed is variable. Those hours don’t always coincide with the hours of peak energy demand. A school or office building might be empty on a sunny weekend afternoon but bustling early on a winter morning with little or no sun. Excess energy could be fed into the grid where the utility offers net-metering options. This would reduce the overall cost of energy for the property owner or operator; however, it does not contribute to the reduction of peak demand, nor does it improve resiliency or reliability during an outage. As an alternative, the excess energy could be stored in an Energy Storage System (ESS) for later use or converted to thermal energy. The logical synergies between solar energy generation and energy storage, often referred to as Solar+Storage, also extend to the reduction of peak demand loads.

A heat pump water heater can efficiently convert solar energy to hot water for use that same evening or the following morning, and excess solar energy can be used to freeze ice storage for the following day’s cooling. Useful heat can also be recaptured from drain water or exhaust air, either to be used immediately or stored for later use. The use of such systems takes stress off the grid during peak events, reduces demand charges, and reduces overall energy use and carbon emissions.

Multiple energy storage technologies have been developed and are currently available; other emerging technologies are in different stages of development. The most common type of ESS consists of lithium-ion batteries arranged on a rack. This is the same battery technology used in small electronics and in electric vehicles. Due to the popularity of electric vehicles, the cost of lithium-ion batteries is in decline.

One example of efficient use of energy generated from on-site resources, such as PV panels, produces energy during the hours of peak production, stores it in an ESS, then transfers that energy onto the battery of an EV for use the following day. ESS has also been used successfully in remote areas where access to the grid is impractical. One such location is the Energy Conservation Management Division in Cimarron, New Mexico, a fire command center for the state’s northwestern region.

Resources

Visit the International Code Council energy resources page for more information.

Net Zero Energy and Decarbonization Toolkit

Toolkit

We are in the final phases of development of the Net Zero Energy and Decarbonization toolkit! This is a resource for states, tribes, local jurisdictions, and other organizations interested in developing and implementing advanced energy efficiency and carbon reduction goals. We are currently integrating new information and resources as they become available.


 

Net Zero and Decarbonization Contact Information

Dave Walls
Vice President
Business Initiatives
3060 Saturn St #100,
Brea, CA 92821
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+(202) 730-3978 or +(888) 422-7233, ext. 6239