How Homes For Cars Can Emit as Much Carbon as Homes for People

A study of the sources of upfront carbon emissions yields some surprising results.

Enterprise Centre
The future of architecture: wood frame, thatch cladding.

credit: Architype Architects

It started as an exercise at the John H. Daniels Faculty of Architecture, Landscape, and Design at the University of Toronto led by visiting professor Kelly Alvarez Doran, asking the question “How do we halve the greenhouse gas emissions of Toronto’s housing stock this decade?” It ended with a dramatic demonstration of the importance of the upfront carbon emissions (more commonly known as embodied carbon) from making cement. These emissions are unregulated and are not taken seriously by many people, but understanding their significance changes the way you think about making just about anything.

The biggest driver of emissions:

"Cast-in-place reinforced concrete was the largest driver of emissions across all projects. Low-rise projects that employ wood-frame structures above a concrete foundation have roughly half the embodied footprint of projects that use reinforced concrete for the project’s entire structure. The lowest-carbon mid-rise project employed a steel-and-hollow core structural system, which resulted in dramatic reductions to total volumes of reinforced concrete per square metre." 

That result will be no surprise to Treehugger readers; we have often suggested that all low-rise buildings should be wood. The next biggest driver is also no surprise: avoid cladding systems that include foam insulations, especially extruded polystyrene. This is happening anyway because of its flammability. And despite the aluminum industry's protestations that their product is benign because so much is recycled, Alvarez Doran says "aluminum’s sourcing and smelting is also extremely energy-intensive, resulting in relatively high embodied emissions compared to other metals."

Housing Cars Can Be Half the Carbon

Below grade embodied carbon
Below grade embodied carbon. Towards Half: Climate Positive Design for the GTHA

But the most remarkable finding of the study was the amount of carbon released into the atmosphere making the materials that are not even for housing people above grade, but that is for storing cars below grade.

"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 percent of each project’s total volume of concrete was below grade."

So as much as half the embodied carbon emissions in our buildings goes into storing the machines that create a quarter of the operating emissions, how silly is this? Doran has a few recommendations: "Reduce/limit on-site parking requirements or allowances, review how sub-grade floor area is accounted for in coverage calculations, and incentivize the reduction of sub-surface floor area." If parking floor area was included in building area, it would disappear pretty quickly.

Complexity Causes Carbon Emissions

Building Section
Complexity Causes Carbon Emissions. “Towards Half: Climate Positive Design for the GTHA,”

Another thing we keep going on about on Treehugger is what we learned from engineer Nick Grant, about the importance of simplicity. But in Toronto where this study was done, buildings are often complicated by setback requirements where the building abuts residential areas to minimize the shadows on all the single-family houses next door. Parking spaces are also not the right width to get efficient apartments, so complicated transfer structures are put in to mediate between the parking grid and the residential grid. Both of these complications increase carbon footprints. Recommendation: "Review embodied carbon impact of step-backs and weigh against other impacts."

The size of the upfront emissions from the parking garage surprised me, as it did Doran, who tells Treehugger:

"I did not anticipate underground parking being such a big driver... but this is why we do research in academia isn't it? Ask the questions the industry hasn't bothered to ask as yet. I did anticipate foundations as a whole however and think that the basement as a Canadian assumption needs interrogation."

He notes, as I often do, that embodied carbon is not well understood, not discussed much, and until recently, not even taught in schools. "I did anticipate foundations as a whole however and think that the basement as a Canadian assumption needs interrogation."

"[It's] proof that architectural education needs to look outwards to empower the next generation of students. The sustainability I was taught a decade ago has proven to be flawed and incomplete... solely focused on reducing energy consumption and employing whatever means and materials required to do so. Hoping this moves us all to a holistic, whole-life carbon view of things."

The research is published in Canadian Architect Magazine as an open letter to "Canadian Municipalities and Associations of Architects, Engineers, and Planners" but is relevant everywhere. They should also look at the work being done in the UK by the Architects Climate Action Network (ACAN) (covered in Treehugger here) where they are calling for regulation of embodied carbon, demanding that building regulations include limits on embodied carbon. (read more and download their report at ACAN)

This Is Already Being Done in Denmark

Proposed Danish Regulations
Proposed Danish Regulations. via Passivehouse Plus

The concrete and masonry people will be fighting this, but it is inevitable; rules are already changing. According to PassiveHouse Plus, the Danish government is already rolling out regulations to achieve a 70% reduction in carbon emissions by 2030.

"The policy sets out a staged phasing in and tightening of targets combining embodied CO2 emissions and operational CO2 emissions for buildings, including separate requirements initially for larger and smaller buildings. "

We Have to Start Dealing With This Today

Nobody wants to think about embodied carbon, the implications are too vast; no electric cars, no demolition, none of Elon Musk's silly tunnels – and especially right now, fewer concrete buildings. I wrote earlier about the global carbon budget, and how every kilo of carbon we emit goes against it.

"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 CO2 that is emitted in the making of the materials for that building (the upfront carbon emissions) goes against that carbon budget, as do operating emissions and every liter of fossil fuel used to drive to that building. Forget 1.5° and 2030; we have a simple ledger, a budget. Every architect understands that. What matters is  every kilogram of carbon in every building starting right now."