Patrick Nachlas & Andy Buccino, joined us recently for our Weekly Wednesday Free CEU webinar Series.
If you missed this session, want to rewatch it, or want to share it with a friend or colleague, you can now do so, as the recording and an article on the topic are available below.
The webinar helped attendees understand the crucial difference between embodied carbon (EC) and operational carbon in home construction, emphasizing that while Embodied Carbon is not currently part of the HERS (Home Energy Rating System), it is a significant contributor to a building’s overall carbon footprint—often exceeding yearly operational emissions. Participants learned that materials such as concrete and insulation play a major role in EC, and that new tools, standards, and Environmental Product Declarations (EPDs) are making it more feasible to measure and reduce embodied emissions. The session highlighted that addressing both operational and embodied carbon is essential for a comprehensive approach to sustainability, and revealed that the payback time for EC in new homes can be substantial, leading some to view renovation as a greener option. Many found it eye-opening just how large the EC impact can be, and appreciated real examples, regional differences, and practical methods for incorporating EC into future rating systems.
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As the focus of sustainable building practices shifts from operational efficiency to a holistic view of a building’s carbon footprint, embodied carbon has emerged as a critical consideration. This article explores the findings and methodology of the Massachusetts 100 Home Embodied Carbon Study, which benchmarked embodied and operational carbon in new residential construction. The study demonstrates how HERS raters and energy modeling professionals can integrate embodied carbon assessment into existing workflows, identifies key carbon drivers in building materials and processes, and discusses how these insights are shaping incentive structures and policy in Massachusetts and beyond. The article is intended for housing professionals, builders, contractors, and the general public who are interested in the future of low-carbon construction.
Introduction: Moving Beyond Operational Carbon
For decades, the primary focus of carbon mitigation in the building sector has been on operational carbon—the emissions generated by heating, cooling, lighting, and powering homes. This emphasis has been driven by tangible benefits such as lower utility bills and improved comfort, and it has led to remarkable gains in energy efficiency through programs like HERS ratings, Passive House standards, and the pursuit of net zero energy homes.
However, as operational carbon is steadily reduced thanks to more stringent codes, electrification, and the decarbonization of electricity grids, a new challenge emerges: the carbon emissions associated with the production and assembly of building materials—the so-called “embodied carbon.” Unlike operational emissions, which accrue over decades, embodied carbon is released up front, before a new homeowner ever switches on a light. These upfront emissions are rapidly becoming a dominant factor in the overall climate impact of new construction.
The Massachusetts 100 Home Embodied Carbon Study was designed to quantify and analyze both operational and embodied carbon in residential projects, providing the first comprehensive North American benchmark that integrates mechanical, electrical, and plumbing (MEP) systems into the embodied carbon calculation. The study’s methodology, findings, and implications offer vital guidance to professionals seeking to address the full lifecycle emissions of homes.
Understanding Embodied Carbon: Scope and Significance
Embodied carbon refers to the greenhouse gas emissions generated throughout the lifecycle of building materials, from resource extraction and manufacturing (cradle) to delivery at the construction site (gate). In the context of lifecycle assessment (LCA), this is typically designated as stages A1-A3. These emissions include the processing of concrete, steel, wood, insulation, and other materials, as well as their transportation and initial installation.
While operational carbon (stage B6) remains important, data from the study confirms that embodied carbon constitutes a significant share of a building’s total emissions. For the average home in the Massachusetts study, approximately 55.5 tons of CO2-equivalent were emitted before the first occupant moved in. By comparison, annual operational emissions for these homes were about 3.1 tons, meaning it takes nearly 18 years of operation to match the carbon footprint incurred during construction.
Globally, embodied carbon accounts for roughly 9% of building-related emissions—a figure that is rising as operational emissions fall due to advances in energy efficiency and the growth of renewable energy. In the U.S. alone, annual embodied emissions from new residential construction are comparable to the total emissions of entire countries such as Austria or Greece.
Why Embodied Carbon Matters Now
The urgency of addressing embodied carbon stems from the time value of emissions. Upfront carbon is released immediately, contributing to atmospheric greenhouse gas concentrations when mitigation is most critical. Delaying action on embodied carbon risks overshooting near- and mid-term climate goals—even as buildings become more efficient in their operation.
Moreover, as codes and practices drive operational emissions downward, embodied emissions become the “next big bar on the chart”—the next frontier for meaningful carbon reduction in the built environment. Builders, designers, and contractors who understand and act on this challenge will be leaders in the evolving landscape of sustainable construction.
Methodology: Integrating Embodied Carbon Assessment into Residential Practice
The Massachusetts study was groundbreaking in several respects:
- It centered HERS raters as the key workforce for embodied carbon assessment, leveraging their existing expertise in building science and energy modeling.
- It integrated MEP systems into the embodied carbon calculation, providing a more complete picture of total building emissions.
- It aligned its methodology with the newly released RESNET 1550 standard, which establishes protocols for embodied carbon data collection and reporting in the residential sector.
Data Collection and Analysis Workflow
Participation in the study was limited to dwelling units registered with RESNET and built between 2023 and 2024 in Massachusetts—a state where over 90% of new homes undergo HERS rating. To streamline the process, the study team developed an “integration sheet” that allowed data from energy modeling software (such as Ecotrope) to be efficiently transferred into BEAM, a free embodied carbon calculator.
HERS raters were trained to supplement their usual data collection with additional inputs needed for embodied carbon analysis, such as material quantities for foundations, partitions, and garage areas that are typically omitted in standard energy models. The study found that approximately 60-70% of the data required for an embodied carbon assessment is already captured during a typical HERS rating, making the additional workload manageable after initial training.
To quantify the emissions associated with each material, the study relied on Environmental Product Declarations (EPDs)—third-party verified documents that specify a product’s global warming potential per unit of measure. Where product-specific EPDs were not available, industry-average values were used.
Key Findings: Embodied Carbon Baselines and Drivers
- Average Embodied Carbon: The average upfront embodied emissions for the 100 homes studied was 55.5 tons of CO2e per dwelling. This figure provides a crucial baseline for future policy, incentives, and design improvements.
- Operational vs. Embodied Carbon: With operational emissions averaging 3.1 tons per year, the initial 55.5 tons of embodied emissions represent a substantial “carbon debt” that takes nearly two decades to offset through efficient operation.
- Variability and Opportunity: The study observed a wide range of embodied carbon results, from as low as 20 tons to as high as 144 tons per home. This variation indicates significant opportunity for reduction through material choices and design optimization.
- Key Material Contributors: Concrete emerged as the single largest contributor, responsible for about 40% of embodied emissions, followed by MEP systems (18%) and insulation. Windows, while significant in commercial buildings, were less impactful in the residential context studied.
- MEP Systems: The inclusion of MEP systems in the embodied carbon scope is notable. While energy models can often estimate heating and cooling equipment based on capacity and duct area, some components (such as wiring) must be approximated by building size to avoid excessive data collection burdens.
- Intensity Metrics: When normalized by building size, the average embodied carbon intensity was approximately 226 kilograms CO2e per square meter, consistent with similar studies in North America.
Workflow Feasibility: Training and Quality Assurance
The study’s approach to integrating embodied carbon assessment within the existing HERS workflow was validated by the experience of 16 raters, whose average time to complete an embodied carbon assessment dropped from over three hours to less than one hour as familiarity increased. While early projects required more effort—especially for homes rated months or years earlier—the expectation is that real-time assessment in tandem with operational ratings will further reduce the burden.
ResNet’s emerging quality assurance protocols for embodied carbon will help ensure data consistency and reliability, mirroring the success of HERS as the “gold standard” for operational energy assessment.
Implications for Policy and Market Transformation
Massachusetts is already embedding embodied carbon reduction into its building code and incentive structures. Builders can earn HERS point adders for using low-carbon concrete or achieving a low-carbon shell, effectively trading modest increases in energy efficiency for substantial carbon reductions in materials. This approach recognizes that embodied and operational carbon are distinct but complementary, and that both must be addressed to achieve true decarbonization.
The study’s findings provide a defensible baseline for policymakers to set targets, utilities to design incentives, and builders to benchmark their performance. As the market for low-carbon materials matures and the integration of embodied carbon assessment becomes routine, substantial reductions are within reach.
Looking Ahead: The Path to Holistic Carbon Accounting
The Massachusetts 100 Home Embodied Carbon Study demonstrates that embodied carbon assessment is both feasible and impactful in the residential sector. By leveraging existing energy modeling infrastructure and workforce, the additional burden is minimized, and the path is paved for rapid adoption as software tools evolve.
The study also highlights the need for clear metrics, robust data, and ongoing training. As embodied carbon becomes embedded in codes, incentives, and green building certifications, builders and contractors will be increasingly called upon to make material choices that balance performance, cost, and climate impact.
The ultimate goal is a holistic carbon index that integrates both operational and embodied emissions, allowing for true “low-carbon” certification of new homes. While this remains a work in progress, the groundwork has been laid for the residential construction industry to play a leading role in climate action.
Key Takeaways
- Embodied carbon now represents a substantial share of the total carbon footprint of new homes, especially as operational emissions decline.
- The Massachusetts study provides the first North American embodied carbon baseline that includes MEP systems for residential construction.
- On average, new homes in the study emitted 55.5 tons of CO2e upfront, with operational emissions of 3.1 tons per year.
- Concrete is the largest single source of embodied carbon in residential construction, highlighting the importance of low-carbon material alternatives.
- Approximately 60-70% of data needed for embodied carbon assessment is already collected during standard energy modeling, making integration feasible.
- Incentives and policy are beginning to recognize embodied carbon, with Massachusetts offering HERS point adders for low-carbon materials.
- Builders, contractors, and energy professionals will need ongoing training and quality assurance protocols as embodied carbon assessment becomes standard practice.
- The future of sustainable construction depends on addressing both operational and embodied carbon in a holistic, data-driven manner.
Q: Who is updating assumptions on carbon content as production methods improve?
A: The RESNET Carbon Index uses NREL data and assumptions on grid cleanliness over the next 25 years. You can read more about it here.
Q: Is foam an insulation issue versus airtightness in fiberglass properly accounted for?
A: It is not a direct tradeoff. There are many methods to airseal a home. Infiltration rates are accounted for in the operational emissions.
Q: How do ICF homes fare in EC compared to stick-framed homes? Will “green” concrete made from electrochemical/solar electricity cement cut down on its EC contribution in a meaningful way?
A: This was not part of this study. However, we would anticipate any meaningful reduction in embodied concrete emissions would have a substantial impact in the whole home results.
Q: Shouldn’t operational carbon vs embodied be compared “apples to apples”? As shown on the previous slides, the type of building affects the results. Putting all the numbers together might be misleading.
A: No, they are disconnected decision trees. The embodied carbon of the materials selected in a home does not directly correlate to the energy efficiency of the home.
Q: Would this study and EC rating methods be instructive on preserving existing structures (for improved reuse) instead of teardowns, which add yet more carbon?
A: End of life for existing buildings was not included in this study.
Q: What was different in components between high and low embodied carbon projects?
A: Amount of concrete and type of insulation were the two primary contributors.
Please help us keep these webinars and writings going by becoming a supporting GHI member or by making a donation.




someone on LinkedIn told me they decided to switch their ERV system to positive pressure to help keep the smoke from entering the home by pushing the air out the natural leaks in all homes and then using their MERV 13 to filter the incoming air. I wish I had tested this more during the hazardous smoke, but I did switch over to this by moving the exhaust dial to 70 CFM and maintaining 100 CFM on the intake during the next few days when we spent most of the time in the EPA IQA unhealthy and very unhealthy range, and it seemed at least effective there. 





