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Embodied Carbon in the Built Environment

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Portland airport roof under construction shows the wood slats of the roof at the top with a sunny, blue sky with a few clouds in the background behind a construction crane with construction walls inside the building at the bottom.
Embodied carbon is a climate change issue involving GHG emissions from the consumption of goods, building materials and food. Building materials account for 13% of annual global emissions, so reducing embodied carbon in the built environment is a priority to reach net-zero carbon by 2050.
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Image: Image of the PDX airport roof under construction provided by Port of Portland. The wooden roof with mass timber components will cover the airport’s expanded main terminal with mass timber used to create a sustainable design.


The City of Portland is a national leader in decarbonization with programs and policies reducing greenhouse gas emission (GHG) in building operations. However, we cannot achieve net-zero carbon without also addressing the embodied carbon of building materials.

Reducing both operational and embodied carbon emissions

The GHG emissions arising from the manufacturing, transportation, installation, maintenance, and disposal of the building materials used to construct a building are known as embodied carbon. A shorthand way to remember this is that these emissions are from the “body” of the building: the concrete, steel, wood, and other materials.

When people talk about building energy, they typically refer to operational carbon – the emissions that occur from energy usage for space heating and cooling, water heating, cooking, lighting, and the use of electronics. To reduce operational carbon emissions, we can install energy efficient appliances, increase insulation and air sealing in a building, and switch our building energy usage to all-electric appliances and systems to be run by renewable energy sources.

However, the GHG emissions of building materials occurs before any of those operational systems are in use. Unlike operational carbon, very little can be done to reduce embodied carbon after a building is constructed. Embodied carbon must be addressed alongside operational carbon to achieve our ambitious net-zero goal.

Image of a timeline with notation for the different processes (extract raw materials, transport to factory, manufacture products, transport to site, construct the building, use and maintain the building, demolish the building, haul away waste materials, and landfill) with notation that each of these steps includes greenhouse gas emissions in the form of embodied carbon.

Climate impact of new construction

Locally, construction waste and demolition debris accounts for approximately 30-35% percent (by weight) of the landfill bound waste in Portland’s waste stream. The best way to address embodied carbon is to reuse existing buildings instead of constructing new buildings. This adaptive reuse avoids demolishing existing structures and using new building materials. Existing buildings can also be retrofitted to reduce operational carbon emissions.

Unless we take action to reduce emissions arising from building materials, emissions will continue to increase in the following building material lifecycle stages:

  • Raw material extraction and manufacturing: Global demand for construction materials is increasing to accommodate population growth.
  • Transportation of materials: Emissions increase when materials are transported from regions far away from a construction site, requiring long distance transportation of heavy materials to construction sites.
  • Construction waste: Each new construction site generates waste that ends up in landfills.
  • Building end of use: Aging and inefficient buildings often have high operational carbon loads and would be better to replace from an efficiency standpoint.
  • Demolition: Emissions increase when buildings are demolished as the materials release GHGs in landfills or through incineration.

Simply adapting existing buildings won’t be enough to meet the needs of our growing population. An estimate from the American Institute of Architects (AIA) notes that the global demand for new buildings is comparable to constructing one New York City each year for the next 40 years (Architecture 2030). We must address the building materials and methods of new buildings as soon as possible or we lose the opportunity to reduce embodied carbon emissions.

Embodied Carbon Reduction Methods

The best way to impact the embodied carbon of a building is early in the building’s design when structural and material decisions are being made, but construction practices and the end of a building’s use also offer opportunities. Common examples of these methods include:

  • Constructing buildings using lower-GHG materials such as low-carbon concrete, or bio-based materials such as wood products, straw, hemp, or cellulose.
  • In an adaptive reuse project, the interior or exterior of a building is remodeled or altered a way that the building can be used for a different purpose. An example of this would be adapting a former bank building to be office space or a former warehouse to be apartments.
  • Preserving existing buildings for cultural and historical significance instead of demolishing a building and constructing a new building in its place.
  • Purchasing materials locally or regionally in order to reduce the transportation impacts of building materials.
  • Reducing construction waste by designing buildings to require fewer material inputs and developing construction processes that sort materials for reuse and recycling.
  • Deconstructing buildings rather than demolishing in order to recover materials for reuse, avoiding the need to produce the same amount of new materials.

Example City of Portland Policies that reduce embodied carbon

In the Climate Emergency Workplan, the City of Portland supports policies that reduce the embodied carbon of building materials and construction through the use of low-carbon alternatives, adaptive reuse, and whole-building life-cycle assessments (LCAs). The City participates in local, regional, and international coalitions of cities and non-governmental organizations whose missions align with reducing embodied carbon in buildings to share and learn policy practices that will make an impact. Additionally, several plans and policies include provisions that reduce the embodied carbon of buildings in Portland, including the following:

  • The Deconstruction Program requires houses built before 1940 to be deconstructed instead of demolished at the end of use. Salvaged wood is sold by local businesses and reused in other buildings. Reusing wood locally reduces the emissions associated with harvesting, processing, and transporting virgin wood into the Portland region.
  • The Low Carbon Concrete Initiative established the Portland Area Mobile Mix environmental product declaration (EPD).
  • The Concrete Embodied Carbon Threshold Requirements set a maximum global warming potential (GWP) value for all a set of concrete types used in City-owned or solicited construction projects.
  • The Parking Compliance Amendments Project removes minimum parking requirements citywide and makes other adjustments to parking maximums and parking standards to align with State of Oregon’s Climate Friendly and Equitable Communities (CFEC) rulemaking process. This will reduce the overall amount of concrete used, causing a tremendous reduction in embodied carbon.
  • Portland Clean Energy Fund equitable tree canopy funding will increase carbon sequestration in trees.
  • Low-embodied carbon materials are recommended in residential zoning design standards.
  • The Green Building Policy certifications support sustainable and low embodied carbon materials.
  • LEED green building standards for new affordable housing developments support sustainable and low embodied carbon materials.
  • Promotion of adaptive reuse for office-to-residential conversions with ordinances that reduce project time and cost barriers.

Just Transition to a Clean Economy

BPS’ work on embodied carbon supports a just transition, which centers the people at the forefront of the climate crisis in the global transition to a clean economy. Increasing the use of low-embodied carbon materials will create good jobs for frontline workers in the growing zero-carbon economy, support the creation of new small businesses, create healthier living spaces for Portland residents, and provide opportunities to preserve and honor historic and cultural resources. Low-embodied carbon materials can also support important local economies and practices, such as indigenous land stewardship and sustainable forestry.


FAQ

Which building materials have the highest embodied carbon?

Concrete – Concrete is composed of sand, gravel, cement, and water. Large amounts of fuel are required for heating in the cement production process production and the material also emits carbon as it cures. One method to reduce the carbon impact of concrete is to adjust the formula of the cement towards less carbon-intensive components. If you would like to learn more, this video is informative.

Steel – Melting steel to create building materials such as beams and rebar requires large amounts of fuel. Additionally, there are a limited number of steel manufacturers in the United States, so many steel products are shipped worldwide, adding transportation emissions from steel products in buildings.

Aluminum – Aluminum is frequently used as metal studs in building construction and also as exterior cladding. Similar to cement and steel, aluminum requires large amounts of fuel to produce and transport. An alternative to aluminum is other low-carbon materials such as wood framing, recycled aluminum cladding, or wood or stucco siding.

How do we measure embodied carbon?

A whole building life cycle assessment (WBLCA) is completed to determine the total potential CO2 emissions impact of the building materials. One useful tool to complete WBLCAs is Environmental Product Declarations (EPDs), which describe the origin and composition of a material. The assessment allows building design teams to make materials choices that can reduce the overall carbon emissions of a building design. Learn more about WBLCA.

What can I do?

If you are remodeling or building a home, consider using low embodied carbon materials to reduce your GHG impact and improve the long-term efficiency and comfort of your home. Local re-use materials organizations take donations of and resell durable materials such as lumber, sinks, spare tile, plywood, and hardware to local re-use materials organizations.


Partners:

Additional resources:

Contact

Lauren Zimmermann

Sustainable Building & Deconstruction Specialist

Sonrisa Cooper

Sustainable Economy and Just Transition Analyst