Embodied carbon is the carbon dioxide (CO₂) emissions associated with materials and construction processes throughout the whole lifecycle of a building or infrastructure. It includes the emissions produced during the manufacturing of building materials (material extraction, transport to manufacturer, manufacturing), the transport of those materials to the job site, and the construction practices used. It also includes the emissions produced from maintenance, disassembly or demolition, transportation of waste and recycling.

The production of building materials and products are typically energy intensive processes. Large amounts of embodied energy, water and carbon are generated for each built asset, in our current linear economic model of “take-make-use-dispose”. When embodied carbon (the emissions from materials and construction) is added to operating emissions, the built environment is responsible for almost 50% of emissions in the USA, notes the American Institute of Architects, and as building operations become more carbon efficient, the proportion of total emissions from the emissions from producing building materials is set to rise. Embodied carbon is more difficult to measure and track than operational carbon, which is relatively simple to extrapolate from occupants’ energy bills.

While the last 30 years of green-building oriented efforts have focused on the reduction of operational carbon to make buildings more efficient during use, the industry recognizes the significant embodied carbon footprint of the built environment must also be considered to reduce overall emissions generated. As the world’s building stock is expected to double by 2060 addressing embodied carbon is a critical element in mitigating the effects of global climate change, improving public health, boosting the global economy, and maintaining biodiversity.

For embodied carbon, the design phase is the key opportunity to reduce the level of carbon emissions. Research and papers aimed at influencing regulations and policy to address embodied carbon include the Architects Declare launched in 2019 by 17 Stirling Prize recipients. Architects Declare has global reach across  28 countries with over 7,000 signatories to date. Its agenda addresses the climate and biodiversity emergency through practitioner roadmaps, workshops, videos, and advocacy activism. In 2021, RIBA and Architects Declare jointly published the Built For The Environment Report ahead of COP26, which has been instrumental to advancing carbon footprint discussions to initiate policy change. The report has been signed by numerous construction sector stakeholders globally, from architectural designers, to NGOs, professional institutes and bodies, academia, builders, contractors, investors, and property developers.

To that extent, transparency is required from the industry, to make disclosure of carbon content mainstream and improve the decision-making process of designers that enable the greatest transition to low embodied energy building materials.

The Potential Impact of Embodied Carbon

We must take action immediately to reduce emissions arising from construction materials manufacturing. Embodied carbon must be addressed because its impacts will be exacerbated by the increased global demand for construction materials to accommodate population growth, particularly in cities. Improvements in embodied carbon will be multiplied as the replacement of aging infrastructure, which in the US is an investment of approximately USD 4.6 trillion, according to the American Society for Civil Engineers Infrastructure Report Card. The decreased relative proportion of emissions from building operations as building energy efficiencies continue to improve mean that the importance of addressing the footprint of materials will continue to grow. 

Lifecycle Assessment (LCA) is a powerful tool to weigh design alternatives when it comes to the embodied carbon of materials used. Measurement is conducted on a cradle-to-gate basis for products and materials or cradle-to-grave which is commonly used for buildings. Embodied greenhouse gases are estimated in terms of global warming potential, or kgCo2eq per each material over a 100-year period. LCA provides tangible, hard data that allows embodied greenhouse gas emissions to be measured and efficiently substantiate claims of sustainability and emission reductions. LCA calculations are currently required by most green building labels, which has supported the growth of their use as a sustainability tool worldwide.

Reductions in embodied carbon are very effectively enabled by the appropriate design strategies, such as designing with less material, as well as by tackling the intrinsic qualities of materials, and using viable alternatives that have a lower carbon footprint.

In nature carbon is a building block of all living organisms, and present everywhere in abundance. The problem is not intrinsic to carbon itself, but with fugitive carbon, or the excess carbon that is released in the atmosphere, explains William McDonough. We need a new language for carbon where we shift our thinking to consider carbon as a nutrient - and start designing with it. This effectively means retaining carbon in building materials, through building and material longevity and reuse.

Experimenting with cultivated rather than extracted materials, bio-based materials, and responsibly sourced (or salvaged) wood, are a few of the possible applications. In addition, we can rely on current industry progress to capture carbon from the atmosphere and work it into building elements, such as concrete carbonation technologies. Finally, we can incorporate carbon sequestering materials in our design, which are generally bio-based materials such as wood, straw, bamboo, rammed earth. All these design choices lead to a circular, closed loop of carbon. Using agricultural products that sequester carbon can make a big impact on the carbon footprint of a project. Wood may first come to mind, but you can also consider options like straw or hemp insulation, which - unlike wood - are annually renewable.

Francis Kéré, Holcim Awards prize winner and Pritzker Architecture Prize laureate promotes a Burkina Faso architecture that is locally anchored, independent from European archetypes and using local materials: We love Europe – but in the end, we’re just left with cheap copies.” By resourcing to vernacular architecture, not only the local identity is preserved, but the sourcing thereof promotes local economy and employment opportunities. All in all, a Burkina Faso building in clay is a more equitable solution. Kéré’s school project in Gando explores the possibilities to cast with clay as we cast with concrete.

A larger footprint in the global North

Embodied carbon is a topic of less relevance for the global South than for the global North. Highly developed countries have a built environment with higher emissions footprint by using technology-dense processes and highly sophisticated materials, which accrue high resource extraction and production footprints, and multi-tiered supply chain emissions resulting from transportation and logistics. 

To put this into perspective, let’s look at some numbers. According to the Circularity Gap Report 2022, low-income countries (such as India and Niger) which are home to 48% of the world population, consume 19% of global resources and generate 17% of emissions. Whereas high-income countries (US, EU, Japan) are home to a minority of the world’s population but consume 31% of resources and generate 43% of emissions. It is clear where priorities lay, especially in view of the rapid growing population and demand for buildings and infrastructures in the coming decades.

Engineered bio-based materials

Circular material technologies for the biological cycle have led to innovative, engineered products made of agricultural waste, or of processed natural materials such as wood. Some applications are kept as pure as possible. Some go as far as exploring into biomimicry solutions of plant symbiosis, as is the case of moss grafted bio-ceramic tiles. Some others are obtained with addition of biopolymers and bio-based binding ingredients.

The predominant building materials with high-impact potential for emissions reductions include concrete, steel, wood, carpet, and gypsum board. Using less cement is the most effective way to reduce the carbon footprint of concrete, as well as considering different mix designs for low-carbon concrete, specifying design compressive strengths greater than 28 days, using lower carbon cements, and including non-fossil fuel based supplementary cementitious materials (SCM). Designing for material optimization and efficiency should consider lighter weight slabs, reducing reinforcement, modular construction and ensuring concrete can be recycled at end of life. Designs should consider CO2 absorbing concrete as an architectural finish since structural concrete when exposed to air has the ability to absorb some carbon during its life.

Using steel from electric arc furnaces is the best way to reduce embodied emissions in steel, because EAFs uses high levels of recycled material and can be powered by renewable energy sources. To reduce the embodied carbon from a design perspective, use elements that can be produced using EAF as well as salvaged or reclaimed structural steel. Joists and trussed members are often lighter and can support the same weight compared to heavier rolled shapes. In addition, to design for adaptability and deconstruction use structural steel framing that is well suited for deconstruction and reuse due to the use of metal fasteners and standardization.

Using reclaimed wood or wood from climate-smart forests that was manufactured without fossil fuels, and prioritizing the longevity of wood-constructed buildings, are the best ways to reduce the carbon footprint of wood products. Reducing embodied carbon for timber can be achieved through specifying locally harvested and manufactured wood products, selecting wood from energy-efficient manufacturers and air-dried products. The negative ecological and carbon impacts of harvesting primary (old growth) forests are significant. Primary forests store more carbon in vegetation and in soils than do younger forests; logging them not only results in the emissions of this stored carbon, it also undermines biodiversity and ecological complexity, threatening species that rely on mature forests for their survival. To minimize these impacts, only specify wood from new growth, climate-smart forests. At the design stage, a focus should be placed on designing for longevity, reuse, and durability. Look for low-carbon alternatives, design for efficiency and examine environmental product disclosure (EPD) information carefully. 

Embodied Carbon Can Only be Reduced at the Design Stage

Unlike operational carbon emissions the embodied energy and carbon cannot be reversed. Once a design is specified and construction completed, the opportunity for improvement has passed. An embodied carbon assessment should be undertaken that includes:

• Streamlined carbon footprint assessment for planning statements
• Advice on reducing this footprint via design
• Detailed emissions assessment of whole buildings and construction assets
• Carbon footprint assessment of products

Only through highlighting the importance of design can we create the greatest reduction in carbon emissions through zero carbon buildings.