The biggest near-term carbon impact of new buildings is by far that of embodied carbon. United Nations data reveals that embodied carbon will account for nearly half of total emissions from new buildings between now and 2050. Urban growth assessments project this is the equivalent of constructing a New York City monthly for the next 40 years. That’s a lot of embodied carbon.
The concept of embodied carbon is simple enough. It is a measure of carbon emissions produced during building implementation, outside of building operations. This starts with material extraction, transport, rounds of processing, fabrication and assembly, right up to and including onsite building construction. Add to that emissions resulting from maintenance, repair and renovation activities during the operational cycle and end-of-life activities (recycle, reuse, disposal), and the result is embodied carbon.
Embodied carbon matters now more than ever because of the time-value of carbon. The concept of the time-value of carbon highlights the depreciating value of carbon savings over time with respect to mitigating the impacts of the climate change emergency. In other words, the more near-term the savings, the higher the value. Reducing the embodied carbon footprint of new buildings is by far the most effective way of achieving near-term carbon reductions.
Embodied vs. operational carbon
For many years, the focus of design activities has been on reducing operational carbon—the carbon emissions created through building use and operation. While embodied carbon is “baked” into a building at the time of completion, operational emissions start from zero upon building occupation and build incrementally over the service life of the building.
Because of the focus on operational carbon, we have been designing with only half of the equation in our pursuit of carbon reduction by focusing on operational carbon and ignoring embodied carbon entirely. Where performance upgrades hold the promise of improving operational carbon emissions as we move forward in time, the embodied component is fixed upon building completion. Even if all new buildings were to become net-zero energy today, there would still be massive embodied carbon impact.
Strategies to reduce embodied carbon
Material selection
Material selection is an obvious strategy to reduce embodied carbon emissions, and there is progress on this front. Environmental product declarations provide key metrics in material selection, and organizations like Architecture 2030 offer tools and resources, such as the Carbon Smart Materials Palette.
Extended service life
Another potentially powerful, but largely neglected, strategy is to extend the service life of a material, component, assembly and building.
Doubling the service life approximately halves the lifecycle of embodied carbon.
Extending the service life requires discussion of durability and its significance in buildings. The consideration of durability pulls forward a host of related considerations that are seldom included in building programs—considerations that support strategies to extend service life, including maintainability, repairability, upgradability and adaptability. This also requires discussion of broader issues for which there has been little consideration or convergence in practice: how long a building should last, how long its façade system should last, and just what are the causal forces of building obsolescence anyway?
End-of-life activities
A third strategy addresses end-of-life practices for reuse, recycling and disposal of buildings.
The strategies to reduce embodied carbon present challenges for the glass and glazing industry. Ponder one of these considerations—maintenance. How might the glass industry employ a strategy of maintenance to significantly extend service life to more appropriately match the service life potential of, say, float glass in an insulating glass unit? Do we bond the entire assembly together in a manner that defies both recycling and maintenance and, furthermore, collapses the service life potential of the glass from hundreds of years (at least) to a mere 25 years?
Another example: do we bury the business end (air and vapor barrier) of a unitized curtain wall stack joint in a channel where it cannot practically be inspected, repaired or replaced for the service life of the façade system?
These considerations force a change in the way we think and design. We need to give priority consideration to the usability of the buildings we build today as they age into an uncertain future. Economic and social conditions may demand their uninterrupted use well beyond current service life expectations.
Embodied carbon dilemma
The best way to reduce embodied carbon emissions is to stop building. In other words, the greenest building is the one unbuilt. However, I understand this concept is a nonstarter. Nonetheless, I have for the past few years been telling my colleagues, somewhat playfully, that the best thing they could do to move us toward a more sustainable built environment is to slow down. The suggestion garnered a few wry grins and an occasional chuckle. That idea also seemed a nonstarter.
However, I’m sitting in my home office in mid-April writing this in the midst of the COVID-19 lockdown. I’m astonished at the breathtaking speed with which the entire world downshifted. I would have never thought it possible. It’s hard to talk about this experience positively; it’s just too painful for far too many. But in some ways, the virus is forcing us to do things that we should be doing proactively to prevent the looming catastrophe of climate change. Hopefully we will learn and carry much from this experience forward.
Whatever you do, keep your eyes open for the next potential disrupter. The architectural glass and curtain wall industries, and indeed the entire building industry, are ripe for disruptive change, and COVID-19 has demonstrated just how fast that can happen.
The National Glass Association developed a resource to help industry officials navigate building life cycle measurements, including embodied energy.
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