Emissions from the built environment are a significant contributor to the global climate challenge, accounting for a large portion of worldwide greenhouse gas output. While attention has often focused on the energy consumed during a building’s use, a substantial amount of carbon is released long before the lights are even switched on. This “upfront” carbon, known as embodied carbon, represents the emissions associated with the materials and processes required to construct the building itself. Managing these material-related emissions is becoming an important part of meeting global climate goals.
What Embodied Carbon Encompasses
Embodied carbon is the measure of all greenhouse gas emissions, calculated as carbon dioxide equivalent (CO2e), released across the life cycle of building materials and products. This measurement method, known as Global Warming Potential (GWP), converts the climate impact of gases like methane and nitrous oxide into a single comparable unit.
The primary sources of these emissions fall into the initial stages of the material supply chain. This includes the energy consumed for raw material extraction (such as mining iron ore for steel or quarrying limestone for cement), the intensive processing and manufacturing required to transform these raw ingredients into usable construction components, and the transportation of finished materials from the factory gate to the construction site.
This carbon is essentially “locked into” the building’s structure the moment construction is complete. Because these emissions are released immediately, often years or decades before the building’s operational life is over, they have an outsized impact on meeting short-term climate targets. Tracking this upfront carbon is a prerequisite for achieving decarbonization in the construction sector.
The Building Carbon Life Cycle
The full timeline of a building’s carbon emissions is analyzed using Life Cycle Assessment (LCA), a methodology that systematically accounts for all environmental impacts from the building’s inception to its end-of-life. This assessment is commonly divided into standardized modules. The first segment, known as the Product and Construction Stages (A1-A5), covers the emissions released before a building is occupied.
Modules A1 through A3 represent the “cradle-to-gate” emissions, covering raw material supply, transport to the factory, and the manufacturing process itself. Modules A4 and A5 account for the remaining pre-occupancy emissions: A4 is the transport of finished products to the construction site, and A5 covers the energy and waste generated during on-site assembly and installation.
Beyond the upfront phase, the assessment tracks emissions throughout the building’s Use Stage (Module B). This module accounts for carbon associated with maintenance, repair, replacement of materials, and refurbishment over the building’s lifespan. The End-of-Life Stage (Module C) includes emissions from demolition or deconstruction, the transport of resulting waste, and the processing and disposal of materials.
The Difference Between Operational and Embodied Carbon
A building’s total carbon footprint is comprised of two components: embodied carbon and operational carbon. Operational carbon refers to the greenhouse gas emissions released during the building’s active use, from the energy consumed to heat, cool, light, and ventilate the structure. These emissions are continuous, occurring throughout the decades a building is occupied, and are tied directly to the building’s energy efficiency and the source of its power.
Embodied carbon, in contrast, is released in distinct, finite stages tied to the physical materials, occurring either upfront during construction, or later during maintenance and demolition. Unlike operational emissions, which can be reduced over time through energy efficiency upgrades or the transition to a cleaner electricity grid, embodied carbon is locked in the moment the building is constructed. This “time-value of carbon” makes addressing upfront emissions essential for achieving near-term climate goals.
The distinction between the two types of emissions has become significant as the construction industry has focused on energy efficiency. As new buildings incorporate better insulation, high-efficiency systems, and renewable energy sources, their operational carbon footprint shrinks. This reduction shifts the balance, causing the embodied carbon portion to grow in relative importance, projected to account for nearly half of the total carbon footprint of new construction over the coming decades. Minimizing the material-related emissions has become the new frontier for decarbonizing the built environment.
Reducing the Carbon Footprint of Materials
Mitigating embodied carbon requires interventions at the material and design stages of a project. One effective strategy involves material substitution, which means specifying products with inherently lower carbon footprints. For example, replacing conventional concrete (a material with high embodied carbon due to cement production) with low-carbon concrete mixes that use supplementary cementitious materials can reduce emissions.
Structural systems can also be redesigned to use materials that sequester carbon, such as mass timber, which locks away carbon dioxide absorbed by trees during their growth. Beyond material choice, designers can employ material efficiency principles, aiming to minimize the total quantity of material used without compromising structural integrity. This includes optimizing structural layouts, such as limiting column spacing to reduce the required thickness of spanning elements.
Implementing circular economy principles is another strategy for reduction. This involves prioritizing the reuse of existing materials and components from older structures, which avoids the emissions associated with manufacturing new products. Designing new buildings for eventual deconstruction, rather than simple demolition, ensures that components can be easily recovered and reused, minimizing end-of-life emissions and maximizing the materials’ value.