Embodied carbon is a hot topic of discussion in the sustainable design community these days. It includes large amounts of greenhouse gas emissions (GHGs) indirectly tied to building materials due to manufacturing and transporting construction products, the process of construction, building maintenance, product repairs and replacements, building retrofit and demolition.
In GHG accounting, these are known as Scope 3 emissions. Facility managers are already familiar with Scope 1 emissions, which are the direct GHGs from equipment on site, like a gas-fired boiler. Indirect energy-related emissions (Scope 2) may also be familiar—those are the off-site GHG emissions due to production of electricity used in the building, for example, from a coal-fired generating facility run by a public utility.
But Scope 3 emissions, which are all of the other indirect GHGs, are probably more of a mystery. These emissions are associated with products used in the building or consumed by occupants. For example, the GHG emissions from manufacturing copier paper, gasoline combusted in occupant travel to the building, and landfill gases due to waste materials coming from the building.
Most of the embodied carbon in a building is related to the initial construction, which involves consumption of a lot of material and energy resources. But facility management affects a significant component of total lifetime embodied carbon.
During the long lifetime of a building, activities with an embodied carbon impact include maintenance, replacement and renovations—anything that involves consumption of goods. The mantra of “reduce, reuse, recycle” applies here. There is a waste management benefit, of course, but this is also about reducing embodied carbon. The more we can avoid consuming new goods, the more we are avoiding the GHG emissions associated with the production and transportation of those goods.
This “life-cycle thinking” recognizes that products have impact over their entire lifespan, and any effort to reduce environmental footprint needs to look upstream and downstream for the total picture. Otherwise, there is a risk of burden-shifting, or when a benefit in one life phase is cancelled out by an increased impact in another. What if a product with recycled content required much more energy to manufacture than a non-recycled equivalent?
The science for measuring cradle-to-grave environmental impacts is life cycle assessment (LCA). An LCA practitioner looks at all the flows between a product and nature and then models the potential impacts on air, land and water. One of the LCA metrics is global warming potential—this is embodied carbon.
Reducing embodied carbon over the life of the building has a lot to do with maximizing the useful life of products. Choosing durable materials will result in less replacements and save embodied carbon. Low-maintenance finishes reduce the upstream impacts of cleaning supplies and energy used by cleaning equipment. Less frequent painting and other tenant improvements mean less consumption, demolition and waste.
Controlling the waste stream also has embodied carbon benefits. If waste materials can be directed towards reuse (even if in a different facility), this helps avoid global consumption and the associated impacts. Downstream impacts of waste are important too. Materials headed to landfill have embodied carbon due to transportation, landfill management, and, for organic materials, potential emissions of landfill gases, which include the potent greenhouse gas methane.
Paying attention is definitely beneficial for the planet, even if there is not yet any direct financial incentive to reduce embodied carbon. Maybe at some point down the road, a carbon tax will be applied to the embodied carbon in products and the lifetime embodied carbon of new buildings.
Until then, is it possible to make purchase decisions with embodied carbon in mind? Almost. A rising trend is the publication of environmental building declarations (EPDs), a document that summarizes the results of an LCA study for a product. As more manufacturers undertake LCA and publish EPDs, and as EPDs improve in comparability (currently a problem), it will become much easier to bring carbon awareness to purchasing.
Jennifer O’Connor is president at the Athena Sustainable Materials Institute, a non-profit research group and consultancy in life cycle assessment for construction and its materials. www.athenasmi.org