In much of North America, houses are built with concrete basements that are often delivered as unfinished spaces used for storage. And if they are finished, they are often second-rate spaces with low ceilings, tiny windows, and poor air quality. It’s a big load of concrete and foam that nobody sees, that lies beneath the surface, contributing to the upfront carbon emissions that may sink us all.
That’s why I was surprised, once again, by a recent post where Builders for Climate Action calculated that 35.5% of the carbon emissions from homes were from the concrete that forms the footings, foundation walls, and slabs that make up the basement and hold up the house. Another 15% is in the insulation, much of which is rigid foam wrapping the basement. As much as 50% of the carbon footprint of the house is unseen, below grade. An earlier EMBARC study of houses in Ontario, Canada, put it at 60%.
Even more egregious is the situation in high-rise buildings, especially the modern green mass timber ones like the new Apex Center designed by William McDonough + Partners. Its concrete parking structure ends up being the vast majority of its upfront carbon. Because the building is all-electric and powered by renewables and designed for disassembly, that concrete parking structure ends up being almost the entirety of its full life-cycle emissions. I concluded, “As always, it is the cars that are killing us.”
This is what Vancouver-based designer and builder Byrn Davidson and Seattle-based architect Mike Eliason have called “the embodied carbon iceberg” that lies beneath the surface of our greenest buildings. In fact, the greener the building, the bigger the impact.
In an earlier post, “How Homes for Cars Can Emit as Much Carbon as Homes for People,” I quoted Kelly Alvarez Doran, then a visiting professor at the John H. Daniels Faculty of Architecture, Landscape, and Design at the University of Toronto (my alma mater), who noted the impact of the underground parking. Alvarez Doran said, “Foundation works, underground parking structures and below-grade floor area have disproportionate impacts on a project’s embodied carbon. For mid-rise and high-rise structures, between 20% to 50% of each project’s total volume of concrete was below grade.” For buildings with wood above grade, it hits 90%.
Alvarez Doran told Treehugger at the time that we have to change the way we think about buildings and even the way we teach architecture and design.
I am not the first to notice it is particularly galling that we are building all these fancy mass timber green buildings for people and loading them up with what Vancouver building scientist Monte Paulsen calls “carbon bombs” that are housing cars.
The University of Toronto’s Shoshanna Saxe gets it too. Whether they are on the road or in the garage, cars are killing us with their upfront carbon emissions.
Buildings take years to design and years to construct, and of course have a lifespan that goes on for years after that. Every single kilogram of carbon dioxide (CO2) that is emitted in the making of the materials for that building—the upfront carbon emissions—goes against that carbon budget, that ceiling that we can’t break if we are going to stay under 1.5 or 2 degrees Celsius. So do the emissions from every gallon of fossil fuel used to drive to that building.
There are a number of things that could be done to shrink the carbon iceberg. The quickest and easiest being the elimination of parking requirements; one could also reduce the parking requirements to the point that it can be done with surface parking, as they did at Timber House, a building we recently covered. One would also need to make it possible to live without a car, with a good bike, e-bike, micromobility, and transit options.
In the residential sector, there are also many options, including simpler building form factors, multistory designs that have fewer basements per unit of floor area, or simply eliminating basements altogether. I have also admired homes that are built on stilts.
However, the best way to reduce the amount of concrete for housing is to put more units in each basement by building rowhouses or plexes and sharing the concrete among more units. This will also get the density up to the point where you won’t need as much parking.
The embodied carbon iceberg from concrete in basements and parking structures really is like the iceberg that sank the Titanic. Most of it is invisible, it’s bigger than we know, and yet we just cruise along, enjoy the ride, and ignore the risk. It will not end well.
