Embodied Carbon: How do we get to zero?

Building structures with zero embodied carbon may sound impossible. It takes energy and creates an impact to produce, transport, and install building materials. However, it is important to understand that zero does not mean all materials and processes are impact-free. Instead, a net zero embodied carbon structure is one built from materials where the emissions from some materials are offset by sequestration from others.

Getting to zero embodied carbon requires a multi-pronged approach. Through a combination of design optimization enabling dematerialization, decarbonization of the electrical grid, material impact optimization, and the inclusion of carbon sequestering structural solutions, there is a pathway to net zero carbon. Not all of these solutions are available today, but through innovation and development in the market, they could become available in the coming years.

The simplest way to reduce embodied carbon is to use less—either at the building scale or the material scale. Retrofits to existing buildings, though sometimes more time consuming from an analytical and space planning perspective, harness our existing resources and produce significantly less embodied carbon than building new.

Current design practice is to optimize based largely, if not exclusively, on the cost and time of construction. In some cases a building is presented to an engineer with an established grid and the engineer is asked to size the members to provide adequate capacity. In this approach, or one where we look only at time and cost, we miss easy opportunities to use less material. While column transfers, long spans, and offsets are an inevitable par of some designs, they all create a more complex load path and require more material. Early engagement in the design process allows the team to investigate the drivers of these elements and take the forces to ground more directly. Material optimization can also be achieved by challenging the traditional practice of using repeating formwork sizes to simplify construction and instead, introducing more variation in formwork to optimize the volume of concrete used. More geometrically complex optimizations can be achieved through parametric analysis and organic optimization algorithms that allow teams to quickly assess multiple structural solutions.

We must also consider how our design choices today may influence the ability of a building to be deconstructed in the future. We must transition our design thinking from a linear approach, where the end goal is the building, to a circular approach where buildings are thought of as material banks for the future. This will enable future design teams to more easily use salvaged materials.

Decarbonization of the electrical grid will affect different materials to different degrees. Even for materials that are highly dependent on electricity-related emissions, such as steel from an electric arc furnace, emissions depend on the power generation sources supplying the electricity to that furnace, not an overall average. Materials with highly grid-dependent impacts will become cleaner, but that will not affect all systems equally. Many emissions related to the manufacture, processing, and installation of construction materials are not directly tied to changes of the electrical grid.

Material innovation will not be limited to new materials but will include advances and optimizations to “traditional” construction materials. Both design teams and material suppliers must understand what drives the embodied carbon within their materials and what can be done, either through the supply chain or design optimization, to produce functional equivalency through less impactful materials.

Materials that can store carbon dioxide will be the key to offsetting the emissions from other materials. Timber is the most obvious structural material that can sequester carbon dioxide but it is not the only one, and the use of any material will require a clear understanding of the full supply chain.

Mass timber construction provides the possibility that large amounts of carbon dioxide could be stored in our structures, but we must also consider the forestry practices and the emissions from other elements of the supply chain like forestry, glues, and processing. We must consider the full life cycle of natural building materials and investigate other scalable biological processes where materials consume carbon dioxide as they are produced. Researchers are currently investigating opportunities related to biocomposites and carbon sequestering aggregates.

The good news is that by using available elements of all of the above strategies we can make meaningful reductions today. Consider the two “standard” systems shown. Both are traditional steel and concrete systems. However, the bar charts (at top) show how each can be optimized from typical practice with strategies such as metals from electric arc furnaces on cleaner portions of the grid and less impactful cementitious materials.