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Summer 2023: Net Zero

Constructing a Sustainable Future: Net-Zero Cities

Hailey Pedicano, Gabriella Mickel, and John Robison Nolon


  • Discusses local government commitments to decarbonization through net-zero goals.
  • Defines “embodied carbon” as GHG emissions created through the building process.
  • Demonstrates the necessity of local governments in regulating embodied carbon emissions.
Constructing a Sustainable Future: Net-Zero Cities

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Surrounded on three sides by rising sea levels with a landscape extremely susceptible to wildfires, climate change forced Marin County, California, to think quickly about a net-zero future. The county first adopted a Greenhouse Gas Reduction Plan in 2006. By its 2020 update, Marin County had committed to net zero by 2045.

In brief, a net-zero future is one where there is an equal balance between the carbon dioxide (CO2) emitted and removed from the atmosphere. This must be achieved through a multisector combination of emission reduction and removal activities, a key component of which is participation at the local, municipal level. In theory the concept of net zero is consistent; however, in practice the methodology between localities can differ widely. While Marin County’s net-zero ambition is focused on reducing total community emissions, some municipalities such as Evanston, Illinois, are aiming their net-zero approach at municipal operations through its 2021 Municipal Operations Zero Emissions Strategy. Others, such as Fort Lauderdale, Florida, which passed Resolution 21-280, have established a tiered municipal-to-community net-zero approach. This differential between local governments largely depends on a community’s socioeconomic vitality, climate conditions, and other city-specific factors.

Marin County took innovative action quickly to meet its net-zero goal, as evidenced by the county’s Climate Action Plan 2030. The county worked to decarbonize transportation by investing in electric vehicle infrastructure. It launched energy efficiency programs and purchased renewable energy to reduce the usage of carbon-intensive energy. Drawing on its state-delegated land use authority, the county has even offered green building incentives since 2001 and has had regulations in place since 2010 that exceed state building code requirements. To reach net zero, however, Marin County realized it needed to address embodied carbon, and became the first municipality to enact regulations limiting emissions from embodied carbon (see Marin County Code, chapter 19.07).

“Embodied carbon” refers to the greenhouse gas (GHG) emissions that are associated with both the building materials and the life cycle of the construction, demolition, and renovation phases of a building. This includes the extraction of raw materials, manufacture and refinement of materials, transport, and building phase of a structure, as well as its deconstruction. The proportion of GHGs emitted from embodied carbon is significant, encompassing almost a third of the total emissions of the building sector according to the 2021 Global Status Report for Buildings and Construction. Key Visualization Data from the World Resource Institute’s Climate Watch platforms shows primary building material sectors, such as cement and iron steel, comprising 9.3% of total end-use GHG emissions. Moreover, the World Green Building Council’s “Advancing Net Zero 2020 Status Report” theorized that a shift towards low-carbon materials by the building and construction sectors “would affect the total emissions for those materials streams and have an enormous impact on emissions mostly attributed to other sectors through these [high carbon] materials alone. The total potential impact, therefore, of the buildings and construction sector, is far greater.”

Today, American local governments across the country are taking action. From Denver, Colorado, to Austin, Texas, over 100 municipalities in the United States have recognized the crucial role of local action in the race to zero and have, as a result, committed to reaching net zero. However, to do so, it is critical that municipalities begin to follow in Marin County’s footsteps and use their land use and other state-delegated authority to increase low-carbon construction. To date, strategies focused on lowering emissions through reducing embodied carbon have received limited attention, particularly at the local level in the context of land use regulations and building codes. Fortunately, Marin County is not alone in utilizing local authority to reduce carbon emissions associated with building materials and construction processes. As a first step, some municipalities, like Miami-Dade County (see article III of chapter 9 of the Code of Miami-Dade County) and New York City (see Clean Construction Executive Order 23), help de-risk the space by committing to using low-carbon building materials and construction processes for municipal buildings and projects, thus taking on the initial burden of things like the increased need for due diligence (making sure the strategies, in theory, are financially and technologically sound), proof of concept (building big projects with these materials to demonstrate the strategies are practically sound), and working with suppliers that may not be as established. By committing to low-carbon building materials, the public sector is agreeing to take on more risk of being at the forefront of implementing these novel technologies, and higher costs, in the short term to attract more private capital and interest for the medium to long term. Other municipalities, such as Albany, California, and Kings County, Washington, have incorporated embodied carbon into their Climate Action Plans.

This article will demonstrate the necessity and ability of local governments in regulating embodied carbon and decarbonizing the built environment if we truly want to reach net zero.

The transition to a net-zero future requires a multifaceted perspective that considers a whole-building life cycle, as well as structural and resiliency needs.

Local Regulation of Private Development

The Intergovernmental Panel on Climate Change’s Sixth Assessment Report identifies local planning and policy as a critical element in creating Climate Resilient Development. It is not difficult to understand why. Municipalities are uniquely situated to drive innovation in reaching net zero. States have delegated the legal authority over the construction and location of buildings to municipal governments. In order to decarbonize the built environment, leveraging municipal land use authority is a fundamental step. The legal regime that governs land use development is primarily within the jurisdiction of local governments. The unique position of a local government’s land use authority acts as a structural factor that can increase the likelihood of achieving net-zero emissions in the building sector. Thus, local governments, through the adoption of land use laws and the adoption, amendment, or administration of building codes, have significant potential to achieve net-zero emissions: by partnering with state and federal governments, the private sector, and environmental advocates to construct a sustainable future.

Currently, efforts to regulate emissions caused by the use and maintenance of a building are relatively common. These municipal tactics can be seen in building codes that mandate energy-efficient heating and cooling systems or ordinances that require certain LEED energy standards. Unfortunately, a strategy focused solely on operational carbon will not be enough to impactfully mitigate emissions from the building sector.

However, low-carbon building alternatives present a significant opportunity for municipal policy makers to address embodied carbon. Communities have multiple resources within their wheelhouse to enforce embodied carbon policy, as well as the ability to promote the acceleration of low-carbon building materials in the marketplace. These municipal mechanisms drive innovation, from comprehensive plans to building codes, and permit policies to materials programs and zoning ordinances. Accordingly, local governments have a one-of-a-kind ability to mitigate embodied carbon in the built environment.

The Need for Low-Carbon Building

By 2060, the global floor area of buildings is projected to double in square footage. To fully address the future emissions of the built world, cites and developers need to set their attention beyond use efficiency, or the operational carbon of buildings. According to a 2016 literature review of the life cycle energy analysis of residential buildings, embodied carbon accounted for 26 to 57% and 74 to 100% of the total life-cycle carbon emissions of low-energy and near-zero-energy buildings, respectively. Panagiotis Chastas, Theodoros Theodosiou & Dimitrios Bikas, Embodied Energy in Residential Buildings—Towards the Nearly Zero Energy Building: A Literature Review, 105 Bldg. & Env’t 267 (2016). As such, building design teams that seek to minimize both operational and embodied carbon emissions through wood-based products, deconstructed materials, and low-carbon design can significantly reduce a building’s overall footprint.

The transition to a net-zero future requires a multifaceted perspective that considers a whole-building life cycle, as well as structural and resiliency needs. The emergence of low-carbon building alternatives, and the high potential of reducing embodied carbon in reducing GHGs, puts government stakeholders and the building sector in a key position to significantly impact global climate mitigation.

Currently, the federal government and state governments are actively engaged in creating strategies to address embodied carbon. The 2022 Inflation Reduction Act allocates $5 billion to incentivize the use of low-carbon building materials by, among other things, increasing low-carbon materials in General Services Administration–owned buildings, Low-Carbon Transportation Grants to increase the use of low-carbon materials for Federal Highway Administration projects, and additional FEMA grants for public projects that include low-carbon building materials. Also in 2022, California’s Carbon Intensity of Construction and Building Materials Act (A.B. 2446) was signed into law and addresses embodied carbon by requiring the California Air Resources Board, along with other state agencies, to develop a framework for measuring and reducing the average carbon intensity of building materials by 2025.

Private developers, academia, and other organizations are also researching effective ways to mitigate embodied carbon. In 2022, the New Building Institute published multiple articles with specific discussions on the role of decarbonization of new construction and policy formulas in reducing embodied carbon. Additionally, Net-Zero America, a multifaceted study published by Princeton University on getting the United States to net-zero emissions, identified embodied carbon as a part of the strategy, from built design to innovative new low-carbon building materials.

While research in this space continues to grow, there are several currently available building techniques that can be employed to reduce embodied carbon. To start, limiting carbon-intensive materials in new building design is a fundamental approach to reducing new construction emissions. Developers, engineers, and architectural design teams can be incentivized to use less concrete, steel, or other common high-carbon materials.

Additionally, wood-based products can act as alternatives to high-emission materials such as Portland cement. Cross-laminated timber specifically has a higher structural integrity than other forms of timber and can be used in place of foundational building materials. Moreover, wood naturally sequesters carbon, and continues to do so throughout the life cycle of the product. As such, building design teams that seek to minimize both operational and embodied carbon emissions can significantly reduce their overall carbon footprint by using wood-based building materials.

Another key strategy for the building sector’s effort to reduce carbon is through deconstructed material reuse and recovery programs. Reusing building parts and materials in new buildings provides an opportunity for circular production and consumption of materials, while at the same time lowering the overall life-cycle carbon output of a building. Moreover, manufacturers are increasingly improving the ability within major factories to design building parts for disassembly, thus making it easier to reduce the embodied carbon associated with the end-life of buildings. In addition to these existing low-carbon building materials, new market alternatives to carbon-intensive building materials continue to emerge.

New Market Alternatives

Today, concrete is the most consumed man-made material in the world. According to the USGS Mineral Industrial Survey, in 2021, New England and the Mid-Atlantic moved approximately 5,919,934 metric tons in shipments of Portland cement, 5% of the national total. To put that in context, these northeastern regions moved the material equivalent of the Brooklyn Bridge 394 times. The popularity of high-carbon materials like Portland cement poses a serious conflict for cities that endeavor to increase their sustainability. The manufacture of 1 ton of cement alone releases approximately 1 ton of CO2 into the atmosphere.

Fortunately, traditional high-emissions building materials such as steel and cement have new market alternatives. Low-carbon cement innovations such as alternative binders, or low-carbon clinker (manipulated mineral cement substance) alternatives, have the potential to reduce emissions by up to 50%. Notably, due to a processing technique, new forms of cement are being produced with the ability to absorb and store CO2 emissions from the atmosphere. The technology works by collecting carbon dioxide through either point industrial outputs or direct air capture, then using the element as a mineralization tool in production—a process known as mineral carbonation. Given the scale of the global building market, mineral carbonation concrete has the potential to store up to 1 gigaton of CO2 annually.

Developers, engineers, and architectural design teams can be incentivized to use less concrete, steel, or other common high-carbon materials.

There are also innovations in developing a low-carbon footprint from the manufacturing of steel. Most of the current production uses a basic oxygen furnace (production method), whereby 37% of materials are recycled content. This contrasts with electric arc furnaces, which can use up to 100% recycled material without compromising structural integrity. This limits the carbon footprint through lowering the carbon needed to produce new material.

These prospects are exciting but face environmental, technological, and economic barriers. First, the mineral carbonation process requires large amounts of energy, so to produce net-negative results, that energy would likely need to come from renewable sources. Additionally, carbonized concrete faces tough economic competition with established building material types, such as Portland cement, which has low costs and is already produced worldwide. However, research in this space is rapidly catching on. In June 2022, the Department of Commerce held an industry-wide consortium to standardize measurements for regulation and enable acceptance of low-carbon concrete in the U.S. market. Further, municipal action can help improve the economic viability of low-carbon building materials.

Municipal Strategies for Decarbonizing the Built Environment

The following case studies showcase the creative measures implemented by some local governments to reduce embodied carbon.

Green Construction Building Codes—Gaithersburg, Maryland, and Denver, Colorado

One central mechanism through which embodied carbon can be addressed is in the adoption of sustainable building codes. In the United States, the International Code Council (ICC) largely develops the building codes that are then adopted and modified by states and, sometimes, local governments. These codes are then typically enforced through local governments via a building permit process. This relationship enables cities to push the development of low-carbon building within their community.

Common green building incentive programs include fiscal or tax incentives, density area ratio bonuses, and expedited processing of local construction permits.

In 2020, Gaithersburg, Maryland, was the first town in the United States to adopt the ICC’s 2018 International Green Construction Code (IgCC). The current IgCC includes provisions such as having a percentage of materials be locally manufactured, requiring the use of recycled content in a total building project, prescribing low-carbon and environmental materials, as well as requiring an assessment of the total life-cycle carbon emissions of a building project (including calculations of embodied carbon). The ability for Gaithersburg to adopt the IgCC stems from the State of Maryland’s authorization of the code in 2011. Last year, Maryland enacted S.B. 528, the Climate Solutions Now Act of 2022, which required the state to adopt the 2021 IgCC by January 2023. This move by Maryland will allow local governments within the state to address embodied carbon through enforcement of the green construction code.

In January 2023, the Denver City Council formally adopted the 2022 Denver Green Code, another leading step in regulating embodied carbon. Colorado’s Division of Building Codes and Standards regulates certain aspects of the state’s residential and nonresidential construction industry in partnership with local governments, allowing cities such as Denver to expand beyond the minimum requirements of state-adopted codes. The new Denver code includes two amendments that limit embodied carbon of specific materials. Section 901.3.2.1 of the code sets embodied emissions limits for concrete according to compression strength, and section 901.3.2.2 does the same for structural steel. In addition, the steel requirements also mandate that 50% of the energy sourced for steel production be renewable. All submitted concrete products, steel products, and a minimum of 10 other products are required to have Type III environmental declarations (EDP), which gives Denver regulators information on the life cycle of the product. Moreover, 10% of all building materials must be regionally sourced and procured.

Recycled Deconstructed Materials City Policy:San Diego, California, and Pittsburgh, Pennsylvania

As cities and communities expand, older buildings become harder to maintain. Developers often decide not to renovate buildings on newly acquired property, but to instead demolish existing structures and rebuild from the ground up. This already-existing cycle is a great area for enacting low-carbon building policy. Reusing building materials has multiple sustainability benefits, including lowering the footprint of a new construction project, as well as diverting material from landfills.

In April 2021, Mayor of Pittsburgh, William Peduto, issued an executive order on Building Deconstruction. The order includes provisions such as citywide deconstruction standards, hosting deconstruction and material diversion training for construction workers and developers, and creating an incentive program for private demolition permit applicants. In San Diego, code ordinance subsections 68.511 through 68.520 establish the Construction and Demolition Debris (C&D) Diversion Program. The regulation piggybacks off required permits for demolition projects, requiring that demolition teams provide a calculation of building materials they can recover for reuse and allowing them to submit that information for a potential tax credit.

Embodied Carbon Incentive Programs:Seattle, Washington; Arlington, Virginia; and Douro-Dummer, Canada

Cites can also create incentive programs that motivate private developers to mitigate emissions from embodied carbon in new construction. Common green building incentive programs include fiscal or tax incentives, density area ratio bonuses, and expedited processing of local construction permits. Developers often must deal with wait times in permit processing and are subject to zoning limitations on the size of the new buildings. Thus, these incentive programs can directly influence construction emissions by coupling these issues with sustainable practices, making low-carbon building materials more attractive.

The Seattle Department of Construction offers a Priority Green Expedited Program, which shortens construction plan review time by 50% and offers participants a point of contact throughout the process. To be eligible, however, developers must consider opportunities to mitigate embodied carbon emissions and demonstrate efforts to reduce material use. Seattle established the Priority Green Expedited Program in 2009, and it is a part of Seattle’s Climate Action Plan to become carbon neutral by 2045. Additionally, Arlington, Virginia, currently runs a Green Building Density Incentive Program. The program has five levels of benefits for green building, with the highest level specifically addressing embodied carbon through a Zero Carbon certification. While Arlington originally adopted the Green Building Density Program in 1999, it has gone through five updates, including the most recent in 2020, and has proven to be an effective tool for increasing green building within the city. Since 2012, most new developments in Arlington are built with some level of green building commitment.

Other municipalities are taking the leap to regulate private development. In 2020, Douro-Dummer, a township in Ontario, Canada, created Canada’s first embodied carbon reduction program for building construction. Developers receive a 40% building permit fee rebate on projects that meet the required GHG reduction targets, or an 80% building permit fee rebate on projects that meet the reduction targets and net-zero ready construction requirements. Douro-Dummer’s program requires developers to use an embodied carbon calculator tool. The developer enters the overall dimensions of the building and selects potential materials. The calculator compares the total carbon to the program target. From there the developer can adjust selected materials until they meet the target. After completing construction, the developer provides verification documents to receive the rebate.

Low-Carbon Building Zoning Ordinance: Cambridge, Massachusetts, and Vancouver, Canada

Unsurprisingly, a highly effective way to directly regulate embodied carbon emissions of private development is through citywide zoning ordinances. In October 2021, the city of Cambridge, Massachusetts, updated Zoning Ordinance Article 22, Sustainable Design and Development, to align with the city’s updated Net Zero Action Plan. The Action Plan carves out an entire pillar of strategy dedicated to addressing embodied carbon, including requiring an “embodied carbon narrative” within the existing “net zero narrative” and “adaptive reuse study” for all construction projects, encouraging material reuse through fiscal incentives, and promulgating carbon intensity targets for new construction projects. The updated zoning ordinance, in addition to the “net zero narrative” and mandated reporting of total emissions, further requires any rating system used by developers, in collaboration with a mandatory Green Building Professional, must specifically address construction, design, and material choice.

Additionally, Vancouver, Canada, provides a striking model of addressing embodied carbon through regulatory schemes. In May 2022, the Vancouver City Council approved changes to the Vancouver Building By-laws, to be effective July 2023 and 2025. The new by-laws (equivalent to a U.S. zoning ordinance or municipal law) will incorporate an embodied carbon reporting requirement for certain buildings on whole-building embodied carbon impacts and establish an embodied carbon limitation which must not be more than double of a “functionally equivalent baseline.”

Beyond Net Zero? The Role of New Buildings in Carbon Sequestration

As the municipalities discussed above work to decarbonize the building sector, other municipalities are beginning to create a built environment that goes a step further by sequestering carbon. Municipalities with net-zero goals often highlight the opportunity to utilize carbon offsets and sinks after exhausting other means of mitigation. Fortunately, local governments have the authority to permit, incentivize, and mandate the sequestration of carbon in new buildings. One potential opportunity, discussed above, is carbon-sequestering cement. While carbon offsets and sinks that draw on new technology can be difficult to measure and verify, carbon offsets and sinks in the form of green infrastructure (e.g., green roofs and green walls) can provide a natural form of carbon sequestration. They can also result in multiple co-benefits (e.g., improved soil quality and reduced albedo) and be relatively cost-effective compared to other carbon mitigation methods.

In a report entitled Nature Positive and Net Zero, the Urban Land Institute notes that nature-based solutions, like green infrastructure, are often earmarked to provide 30% of carbon reductions. In addition to carbon sequestration, nature-based solutions help address the link between the climate crisis and biodiversity loss. Municipalities have begun requiring biogenic carbon sequestration for buildings. This typically takes the form of requiring building and site designs to have more plants that remove carbon from the atmosphere and fix this carbon within carbohydrates within their tissues.

Local governments like Marin County are paving the way for increased decarbonization of the building sector.

For example, Seattle, Washington, created the Seattle Green Factor, which requires a minimum score for project permit approval based on a weighted menu of points relating to landscape elements like plantings, vegetated walls, green roofs, permeable paving, and other features. Milwaukee, Wisconsin, requires green infrastructure on all large developments. Belvedere, California’s Climate Action Plan states that the city plans to encourage the use of building materials that store carbon. Researchers note that a five-story building can store three times the amount of carbon as a forest taking up the same land area. Perhaps with enough sequestering and mitigative actions (including the use of low-carbon building materials), municipalities could leverage their land use authority to move beyond net zero, towards net negative.

However, advancing municipal regulatory schemes that address embodied carbon must come first. Local governments like Marin County are paving the way for increased decarbonization of the building sector. Low-carbon concrete alternatives and other sustainable building strategies have the potential to transform a high GHG emissions industry to a net carbon sink. Constructing net-zero cities begins from the ground up.