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.

Net Zero Energy

Net Zero Energy - Building Operation Decarbonization

The US Department of Energy defines a zero-energy building as “an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.” Zero energy buildings typically combine energy efficiency and renewable energy in a building to result in net zero energy consumption over the course of a year.

The 2021 IECC includes Zero Code appendices for both residential and commercial buildings. The residential Zero Code appendix is based on the Energy Rating Index (ERI) path of the code. It requires more efficiency than is required in the base code and requires enough onsite or offsite renewable energy production to achieve an ERI score of zero. Renewable energy compliance may happen through a combination of onsite power production, energy generated through community renewable energy facilities, and renewable energy purchase contracts or leases.

The commercial Zero Code appendix is based on the Architecture 2030 ZERO Code, which requires a building to meet the minimum code requirements plus enough on-site or off-site renewable energy to compensate for all the energy anticipated to be consumed by the building.

These appendices focus on the energy use of the building, not the carbon emissions from its energy use. A zero-energy building may still have significant carbon emissions if it utilizes fossil fuels (including natural gas) for space heating, water heating, cooking, or clothes drying.

 

Operational Energy Use

When energy codes mandate higher-performing systems, these quickly evolve from being perceived as risky and unfamiliar special-order systems to being business as usual, at which point the costs moderate. This happens because suppliers, design teams and builders start competing for market share under the new rules, and they develop smarter, more economical means to comply.

To minimize overall energy, use long-term, the code development priority “stacking order” should be based on key strategies with the greatest direct impact on energy consumption:

  • Optimize Envelope
  • System Efficiency
  • Controls
  • Renewable and Recovered Energy

The additional construction cost of high-performance buildings is typically repaid many times over during the life of the building through reduced utility bills. A balance point should be defined to determine the best investment balance point between more efficient systems and more renewables, recognizing that the cost of each continues to fall over time. A second and perhaps more elusive balance point should be selected between on-site and off-site renewable energy generation.

Renewable Energy

Renewable energy, defined in the energy code as the “energy derived from solar radiation, wind, waves, tides, landfill gas, biogas, biomass or the internal heat of the earth,” emits little or no carbon. Achieving a zero energy or a zero-carbon building requires a combination of energy efficiency measures to reduce the building’s load, with remaining end uses met using on-site or off-site renewable energy. The most common type of on-site renewable energy are solar photovoltaic panels. Off-site options can include community renewable energy facilities, power purchase agreements, or other mechanisms enabled by state or local laws and utility policies. The electricity grid, itself, is increasingly powered with renewable energy. However, the specific grid mix varies widely by location. Jurisdictions will need to determine the amount and type of renewable energy appropriate for buildings in their climate zone and grid mix. California, for example, includes a requirement in Title 24, Part 6 that requires solar photovoltaic systems on most new homes.

Renewable Energy Certificates (RECs) represent the “environmental attributes” of energy production from solar or wind, but by themselves are not the equivalent of building and owning a rooftop solar array. Ideally, one would be able to own shares of some large-scale solar array or wind farm and have the energy produced there be treated just as one’s own rooftop solar. Such an arrangement does exist in “community solar” installations, but these are not widely available, especially at large scale.

Low-carbon buildings, especially those which are fully electrified, must be able to shift loads through demand responsiveness, to ensure that functions that draw a relatively large load like storage water heating, building preheating or precooling, or electric vehicle charging, can be done during times when demand is lower on the grid, or when the grid is powered by lower-carbon energy.

Reach Codes

Advanced energy codes and regulations, often known as “stretch codes” or “reach codes,” provide a means to advance energy efficiency in a jurisdiction.  They are a tool to allow more progressive cities and counties with ambitious climate goals to move forward, without having to drag the more conservative parts of the state along. As these stretch code cities demonstrate the constructability and affordability of higher-performance buildings, statewide adoption of such rules is facilitated, generating a virtuous cycle. Notable examples include:

The NYStretch Energy Code is developed by the New York State Research and Development Authority (NYSERDA). Some municipalities, such as Beacon and Hastings on Hudson in New York State, have gone one step further by adopting the advanced model energy code that is more stringent than the State-adopted Energy Code.

The Massachusetts Stretch Energy Code has now been adopted by most of the jurisdictions in that state, providing a much higher level of energy efficiency than is provided by the base code. As most construction now meets the stretch code provisions, further upgrades to the base code may become less problematic for designer teams and contractors.

Washington state has one of the more progressive codes in the country, and the City of Seattle maintains a code that is higher performing still. Seattle’s provisions are regularly adopted by the state in subsequent code cycles.

Boulder, Colorado, is determined to reach a zero-energy code by 2031 and requires buildings over 500,000 square feet to use energy modeling and achieve progressively more stringent efficiency targets. https://bouldercolorado.gov/plan-develop/energy-conservation-codes

California has a well-developed “reach code” program, with dozens of cities and counties participating. This includes not only energy efficiency, but separate paths for advanced code requirements in electrification, renewables, process loads, water use, and electric readiness.

Advanced Codes with a Path Forward

Both Toronto and Vancouver have developed code structures that are strategically moving towards net zero. These are performance-based standards, meaning that they are based purely on energy modeling results rather than imposing specific requirements for equipment or envelope assemblies.

Whereas most North American performance-based energy codes are focused only on overall energy use, Toronto (and Vancouver) codes require compliance with three metrics: TEUI, TEDI and GHGI.

  • TEUI – Total Energy Use Intensity – overall annual energy use, in kWh per unit of floor area
  • TEDI – Thermal Energy Demand Intensity – annual space heating energy, in kWh per unit of floor area.
  • GHGI – GreenHouse Gas Intensity – annual carbon emissions per unit of floor area.

Version 3 of the Toronto Green Standard (TGS) is Toronto’s 2019 step towards a 2030 zero-energy code. Developers of the most common building types can choose either the standard Tier 1 code or else a Tier 2 that’s a 20 – 30% improvement and provides a hefty partial refund of development fees. (15% of projects in the last code version chose the Tier 2 path.)  The current Tier 2 will then become Tier 1 for the next code cycle, and in fact Tiers 3 and 4 have also been defined to flesh out the remaining steps to Toronto’s 2030 zero energy standard

In addition, the TGS includes several prescriptive requirements which are important for ensuring long-term real-world energy performance but can’t be evaluated by using energy modeling. These include

  • Solar readiness
  • District energy connection readiness
  • Air tightness testing
  • Building commissioning
  • Sub-metering
  • Building labeling and disclosure

While the Toronto system is among the most comprehensive and well-vetted of energy code pathways, it is based entirely on energy modeling, which is notoriously over-optimistic when predicting the energy use of highly efficient buildings. Also, it only applies to a handful of specific building types: office, multifamily, retail and education, since high process load buildings (lab, hospital, restaurant, etc.) don’t lend themselves to hard energy use targets. On the other hand, such performance codes reward efficient design choices for building form, orientation and other aspects that would be difficult to pin down in a prescriptive code.

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
U.S.A.
+(202) 730-3978 or +(888) 422-7233, ext. 6239