Achieving Sustainability in the Built Environment, Brick by Brick | Article

Producing roughly 40 percent of global carbon dioxide (CO2) emissions, the building sector, lurking in plain sight, is an often-overlooked culprit of the climate breakdown that grows more apparent by the year. In our efforts to curb climate change through reduced greenhouse gas emissions, it is essential to address the outsized carbon footprint of the built environment.

From the start, choices around building design and materials have a profound impact on construction emissions for years to come, presenting a major opportunity for climate change mitigation. Over the first 10 years of a building’s life, its embodied carbon—that is, the CO2 emissions associated with the production, transportation, assembly, and end-of-life demolition of its materials—makes up about 40 to 70 percent of its total emissions. As federal investment in green infrastructure has ramped up with legislation like the Inflation Reduction Act (IRA) (P.L. 117-169) and the Infrastructure Investment and Jobs Act (IIJA) (P.L. 117-58), an increased policy focus on sustainable construction can offer a direct and effective pathway to emission reductions.

From Cradle to Gate: Embodied Emissions

The emissions associated with a given construction project begin well before any ground is broken. Combined, emissions from the extraction, transport, and manufacturing of raw materials into building materials comprise 65 to 85 percent of total embodied carbon emissions—and 10 to 11 percent of all global greenhouse gas emissions.

The mining of raw materials (such as limestone and iron ore) from the earth is accomplished with heavy, diesel-operated machinery, as well as explosives, which emit nitrogen oxides, carbon monoxide, and other pollutants upon detonation. More emissions are released as the raw materials are delivered to manufacturing plants. The bulk of production-related emissions, however, are released after these materials have been transported. The manufacturing of building materials such as cement (for concrete) and steel requires heating raw materials to extreme temperatures to catalyze the chemical processes that form the finished product. CO2 and other greenhouse gases are emitted during both the combustion of fossil fuels to maintain those high temperatures and the resulting chemical reactions. Globally, the production of cement and steel releases almost five billion tons of CO2 every year.

Tackling Embodied Carbon Emissions at the Source

Changes can be made in building construction—from mining practices and energy sources to material standards and compositions—to help reduce the industry’s carbon footprint. For example, materials like steel and certain types of glass can be manufactured using electricity to heat the raw materials. To further mitigate the building sector’s climate impact, the electricity used to produce these materials should in turn come from renewable resources, such as solar and wind power. As the United States works to build out and transform its electric grid, it must ensure it has the capacity to support electricity-intensive building materials production.

Though the production of some building materials stands to benefit from electrification, cement production is notoriously difficult to decarbonize. The bulk of the carbon pollution from this process comes not from maintaining the high temperatures used to heat the raw materials, but from the resulting chemical reactions that create a key material called “clinker”. These reactions comprise 54 percent of cement production-related carbon dioxide emissions. Recent advancements in research and technology, however, offer promising solutions. Carbon-negative concrete, made from biochar that has been reinforced with concrete wastewater, can sequester CO2 and nearly matches the strength of standard concrete. Pozzolan, made from recycled, powdered glass, can replace up to 50 percent of the cement in concrete with only five percent of the carbon footprint.

The benefits of these emerging solutions extend beyond emission reductions. Producing materials with electricity, for example, is more efficient than with fossil fuels, as less energy is lost in the process. Electrification is also becoming more attractive as extreme heat and foreign production cuts have led to increasing fuel costs. Pozzolan concrete is lighter in color than its standard concrete counterpart, reducing heat absorption in the finished building and mitigating the urban heat island effect.

Policies at the federal, state, and local levels can incentivize or even mandate the use of these greener materials. In August, for example, California finalized new building codes that will require new buildings exceeding a certain size to either be made of low-emission materials, reuse 45 percent or more of an existing structure, or undergo a lifecycle performance analysis. At the national level, the IRA provides over $2 billion each to the General Services

Administration and Federal Highway Administration to procure construction materials with lower levels of embodied greenhouse gas emissions for federal buildings, highways, and transportation facilities.

End of Life: Buildings Reincarnate

However important it is to reduce emissions in the production of building materials, it is also important to change our approach to the end of a building’s life cycle—a phase which accounts for up to 15 percent of a building’s total embodied carbon emissions. The Environmental Protection Agency estimated that in 2018, building demolition in the United States produced 540 million tons of debris, more than twice the amount produced in municipal waste systems. To reduce the emissions and other environmental impacts of building demolition and disposal, policies can create incentives for the sector to reuse and recycle by designing for deconstruction.

“Design for deconstruction” is an approach that aims to construct buildings in a way that will minimize the effort needed to repurpose their parts and raw materials. This is often seen as a critical part of a circular economy, and can simplify and optimize the reuse process. However, design for deconstruction must be used proactively in the planning phase of new construction projects.

To facilitate the reuse of materials from existing buildings, deconstruction is an alternative to demolition that involves more careful planning and execution, and allows for materials to be harvested from a structure that is at the end of its lifespan. While deconstruction does have higher upfront costs compared to demolition, it can also spur job creation, both in the direct work of deconstruction, and by indirectly supporting jobs in material warehousing, retail and sales, and sustainable construction. More market availability of reused materials can help drive policies for clean purchase agreements and emission reduction goals for both public and private construction projects.

Deconstruction is almost always preferable to recycling, which tends to use large amounts of energy to bring products back to a state where they can be remanufactured. However, innovations in research and technology offer the promise of a more efficient recycling process for materials that cannot be deconstructed and reused. The University of Maine, for example, recently unveiled a 3D printed house made from wood-based materials, all of which are recyclable and can be broken down at the end of their lifespan.

The most effective way to reduce emissions from the built environment is to curtail construction altogether by avoiding unnecessary scale of new projects. Additionally, zoning laws could be adjusted to allow for existing buildings to be repurposed after their first use. Jordan Palmeri, an environmental scientist and panelist on EESI’s briefing, Building Materials: From Production to Reuse, pointed to a policy in Portland, Oregon, which limits the size of a single-family home. He also touted the benefits of public requirements for clean purchasing, which creates a starter market for cleaner materials and building practices. EESI’s report, The Value and Impact of Building Codes, emphasizes that investing in sustainability, durability, and potential for reuse from the start can pay dividends in the decades to come by mitigating operating costs, avoiding insurance and damage costs, and staying ahead of public health, safety, and resilience needs.

Together, sustainable practices, policies, and emerging technologies can catalyze significant emission reductions within the building sector. With the implementation of public infrastructure investments from the IRA and the IIJA continuing to hold focus in Congress, policymakers can leverage this spotlight to create standards for sustainability in the construction of buildings and other infrastructure. Public, private, and academic partnerships have already contributed to the research and development of climate-friendly building materials. By strengthening previous laws and investments, policymakers can construct a sustainable future for the U.S. building sector.

Authors: Isabella Millet and Nicole Pouy