“The Future We Choose,” co-written by Christiana Figueres, former executive secretary of the United Nations Framework Convention on Climate Change, gives a sobering view of what the world will look like in 2050 if we don’t cut carbon emissions in half. Buildings have a significant role to play in reducing carbon emissions, yet design decisions to reduce their carbon footprint are complex and fraught with unintended consequences. Misuse of environmental product declarations (EPDs), and pursuing incremental operational energy performance over service life and other embodied carbon factors, are just two related to the building envelope.
This month and next, I am joined by my colleague Alexandra Blakeslee in a dive into this important topic. This month, we explore a hierarchy of decisions for minimizing embodied carbon that can help focus design choices on the highest impact. Next month, we will focus on how to approach design decisions for glass and glazing, and especially how to use (or not use) EPDs.
As Mic Patterson, founder of the Façade Tectonics Institute, asserted in a recent conversation: “The design community wants easy answers for how to reduce embodied carbon, but there just aren’t any. It’s complex.” It is imperative that our industry has a clear understanding of embodied and operational carbon, and a well-defined strategy to delivering the biggest, longest-lasting impact in the shortest time.
What is the Challenge?
First, let us go back to the big picture. In Figueres’ 2050, without action on emissions, we won’t be able to go outdoors without a mask; not because of a pandemic, but because of poor air quality. Large areas of the planet are uninhabitable, infrastructure in coastal cities has been destroyed, and weather disasters and diseases are overlapping and commonplace. And there’s more. The picture painted of the view out of our windows is grim.
The Paris Agreement set targets for the global temperature increase at less than 2°C (3.6°F) this century, in addition to a stretch goal of less than 1.5°C (2.7°F). According to the UN environment programme, we need to cut emissions by 7.6% year over year from now through 2030 to meet the 1.5°C goal.
So, how are we doing? In the first half of 2020, carbon emissions are estimated to have reduced globally by 7 to 9% as compared with 2019. While significant, TIME reports that other dips like this have historically had little impact on the growth trajectory, and The Breakthrough Institute predicts that, assuming economic recovery in the third and fourth quarters, a reduction in emissions of only 2% is likely this year. Reaching the UN’s projected target in the first half of 2020 required a halt to the global economy, which clearly is not a sustainable model. This demonstrates the challenge in front of us all.
According to UN Environment, the building sector is responsible for 39% of global emissions, 28% of which is due to emissions from the manufacturing of building products and construction (embodied carbon). We are accelerating the rate of construction globally and will double the global building stock by 2060. This is the equivalent of building one New York City every 34 days over the next 40 years, according to Architecture 2030. In fact, they predict embodied carbon will account for almost half of total new construction emissions between now and 2050. Curbing embodied carbon is time critical because it is front-end loaded—emitted and contributing to climate change before the building is even occupied.
Embodied Carbon Decision-Making Framework
To avoid unintended consequences and maximize the impact of design decisions, it is important to understand the big picture first before diving into the details. Below is an outline of a decision-making framework and prioritization strategy for embodied carbon reduction:
- To build or not to build? This is the most important question of all. The most sustainable building is the building that is not built, whether we are considering embodied or operational carbon. If a building is needed, can an existing structure be repurposed to use existing resources? Indeed, the choice of location may also be important. Where electrical grids are greener, operational energy consumption may be less important than reducing embodied carbon impacts, although demand still must be managed for renewable grids.
- How small can it be? If fewer materials are used, embodied carbon will be reduced. Presumably, the building will have a lower operational carbon footprint provided all other things are equal.
- How long can it last? If building is necessary, the most impactful decision to its embodied carbon footprint is to ensure that the building and its components last as long as possible. This includes providing paths for easy service, maintenance and upgrades to improve operational performance as technologies become available. Simplistically, doubling lifetimes could halve embodied carbon.Typically, our buildings have a service life of up to 50 years. What does the design of a 100-plus-year building look like in terms of component lifetime, maintenance, service and upgradeability requirements? Typically, façade systems are not designed with this in mind. For example, by making the “chicken head” (upturned leg and gaskets on the stack horizontal on a unit wall system) inaccessible, curtainwall systems are not designed for serviceability nor are they easily upgradeable. This is a key area for the glazing industry to address.Consider the introduction of insulating glass. Patterson has observed that we have taken a material that can last centuries and turned it into a material that now lasts a few decades. This then leads us to the trade-off between operational and embodied carbon. While there is clearly a big jump in building energy performance achieved in going from single- to double-pane insulating glass units (IGUs), is the jump from double- to triple-pane justified when both operational and embodied carbon are considered? Adding a third lite of glass increases the embodied carbon by approximately 150% (order of magnitude, assuming the biggest impacts are from the float process, all lites are the same thickness and treatment). This could potentially reduce the expected service life, all other things being equal, since triple-pane glazing typically experiences higher climate related loads on its edge seals.
A lifecycle assessment would be appropriate to understand these trade-offs and other ways to reduce the embodied carbon impact of triple-pane IGUs. At a minimum, a focus on optimizing IGU durability and extending service life through appropriate material selection, application-specific edge seal design and manufacturing process quality, is critical.
- Target the structural system first then the enclosure: The structural systems— concrete, wood and steel—typically contribute to the majority—up to 80%—of the embodied carbon in a building, and the enclosure contributes around 15% according to Building Green. Cement is typically the largest contributor, and the best strategy is to reduce the amount used (see here for more information).North American steel typically is made with electricity, and with cleaner grids, has substantially lower carbon footprint than imported steel. The same is true of energy-intensive aluminum used in curtainwall and window systems. In the U.S., aluminum production and recycling operations typically use hydro-electric energy, which has limited carbon impact. In contrast, aluminum from China and the Middle East is made from electricity generated by carbon-intensive coal and gas. In addition to only using what is necessary, the most impactful way to reduce the carbon footprint of steel structures and aluminum façades is to specify domestic sources.
Always make decisions related to the structural and enclosure systems with service life in mind, then balance with operational carbon considerations. A greater focus on assessing service life of enclosures and their components, and the impact of changes in thermal performance over their lifetime, will be needed if we are to make sound carbon choices. More on this next month.
The bottom line: A priority on durability and serviceability of specified products and assemblies is key, and this cannot be assessed by looking at a product EPD.