Will the carbon economy ever come for plastic?

Russell Fortmeyer

As the Guardian newspaper reported in July, Marks & Spencer, the vaunted British department store, was denied planning approval for redeveloping one of its two Oxford Street locations in London because of the carbon cost of demolition and new construction. It was an unprecedented move—one widely seen as a victory in environmental circles—and it will certainly influence development decisions in the private sector.

Carbon has become the de facto metric when it comes to gauging sustainable performance in buildings and cities. It is the subtext of every corporate environmental, social, and governance (ESG) report, and influences many design decisions, the result of which is an exploding market for mass timber in buildings. The intense focus on greenhouse gas emissions, or carbon, associated with buildings has largely concerned the bigger material culprits like concrete and steel. They alone may account for up to 40% or more of a building’s embodied carbon at the time of construction completion.

It is no wonder that plastics, which often only show up on a construction site in the form of the packaging of other materials and products, or in the finishes and furniture brought in at the end, have not been the centre of attention in the carbon economy. Packaging gets hauled off a site and generally excluded from embodied carbon footprint analysis. And furniture and other soft finishes for interiors projects are also often left out of analytical models given the relatively loose nature of their association with a specific building (i.e., anyone can remove a chair from a building, so should that improve a project’s carbon footprint?).

For a sustainable materials strategy, however, carbon will be a crucial factor in the next few decades as we decarbonise our cities and buildings. Plastics will have a role to play, even if carbon will never be the most significant environmental criteria to assess their impact on people and the planet.

The UK regulations have incorporated the embodied carbon of a project as a consideration for planning approvals. As professionals, we have seen an increased interest in renovating existing buildings given the benefits in preserving the carbon that has already been paid for, or sunk, in the structure and envelope.

Over the lifespan of a building when including carbon associated with its operation, the materials in the structure, envelope, and the interior finishes, furniture, and other physical elements acquired in the building’s occupancy can easily add up to 60-70% of the building’s footprint. And in an era when buildings are being designed or retrofitted to operate solely on electricity fed by a renewable energy grid, the embodied carbon of our buildings and cities plays a bigger role in addressing the climate crisis.

Policymakers are taking note. Beyond the recent example for Marks & Spencer, in 2022 California became one of the largest economies in the world to adopt a policy, Assembly Bill 2446, to regulate embodied carbon of construction materials starting in 2025, setting goals to reduce embodied carbon by 20% in new and existing renovation projects by 2030 and up to 40% by 2035.

This brings us back to plastics. Although they rarely show up in the big carbon categories like primary structure and envelope, they are sprinkled throughout almost every construction category. If you look at the Bath Inventory of Carbon and Energy (ICE) database, which is the gold standard of general material embodied carbon data and the basis for many lifecycle assessment methodologies in use in industry today, you will see that various plastics appear quite high in terms of their embodied carbon (reported as a carbon intensity factor in kg CO2e / kg of material).

Polyethylene, such as HDPE pipe, clocks in with a carbon intensity factor of 2.52 kgCO2e/kg, whereas a polycarbonate, such as you might find in an architectural panel, is listed at 7.62 kgCO2e/kg. In comparison, a terracotta panel has an embodied carbon of 0.240 kgCO2e/kg. So far, that does not tell you much, as there would certainly be more mass in a terracotta panel compared to a polycarbonate one if you were assessing them in a building project—perhaps less so if you were comparing terracotta pipe to HDPE pipe. Neither calculation considers the end of life of those products and, as we know, terracotta will degrade quite differently from an HDPE pipe left in the ground.

Embodied carbon tools, such as the EC3 calculator (which is available for free and is something we use for testing alternative structural and envelope systems in early planning and design stages), lets you calculate a carbon footprint with those factors based on the quantity of material tagged to the material within a digital model of the project (such as Rhino or Revit). Such models often reveal unexpected conclusions—we may think a “natural” material like terracotta would always make sense compared to an engineered material like plastic, but on a mass basis, it may not pencil out. That also suggests that perhaps carbon is not that useful when it comes to making sustainable choices regarding plastics, but hold that thought for now.

We seldom are making such simplistic comparisons, anyway, since the myriad varieties of plastic we find in buildings and cities tends to be contained in relatively small components within much larger systems (or are excluded as packaging, as noted previously). This is one of the reasons plastic has not been at the centre of the embodied carbon conversation thus far—how would a designer suggest an electrical panelboard manufacturer replace plastic in a circuit breaker housing? And would that even show up, so to speak, in a numerical carbon model of an entire building or city?

The usefulness of such analytical models relies heavily on the quality of the data. The ICE database is a starting point, but it is not locally specific and certainly is not representative of every supply chain and material origin (not surprisingly, it relies much on UK and European sources). Designers and consultants then look for Environmental Product Declarations (EPDs) that are specific to product categories or manufacturers and suppliers to have more accurate carbon factors. Green building certification tools like LEED, Green Star, BREEAM, and Estidama have long had materials credits that incentivise the collection of EPDs for major product categories, but until now there was little external reason for the industry to do much with that data unless a client had specific commitments to reduce embodied carbon.

As embodied carbon starts to factor more into design considerations in every development, we will need more transparency from suppliers and manufacturers. EPDs for plastics as a category may be less relevant than ensuring product manufacturers who rely on plastic feedstocks can obtain quality lifecycle data from suppliers, particularly around the data included in Health Product Declarations (HPDs), which document how a material or product may impact human and ecosystem health.

Perversely, recycled plastics as a feedstock often have higher carbon intensities than virgin material because they require more energy and water to clean up and process for reusing. An EPD would demonstrate that clearly, but exposes the limits of carbon in relation to understanding the sustainable performance of a plastic. One of the reasons recycled plastics are less viable is partly because there is not a solid, large-scale circular economy in place to support investments in efficient collection and processing. That is something manufacturers will have to champion, at least until regulations catch up and either mandate circularity or ask the industry to internalise the costs of environmental pollution from plastics.

Given the nascent regulatory market for embodied carbon and the relatively low contribution plastic makes to an embodied carbon footprint for a building, sustainability and materials consultants have instead scrutinised these other environmental criteria when it comes to plastics. Social justice issues around where plastics are made and how that process impacts local communities, for example, or how plastic can be separated and reused at the end of its life cycle in a building. More pressing are landfill capacities, bioaccumulation of plastics in natural systems, and the reliance on petroleum products in so many plastics on the market. Those will remain critical issues regardless of how we manage to reduce embodied carbon emissions in construction, not just for plastics, but for all materials.

Russel Fortmeyer is the global sustainability leader at global architecture studio Woods Bagot.

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