By Chris Magwood
The focus of green building has long been on reducing impacts… doing “less bad” to the planet and ourselves by shrinking our ecosystem, chemical and climate footprints through conscious design and material selection. But when it comes to our current climate crisis, doing less bad is simply not going to be good enough. The climate science is clear: we collectively need to get to net zero emissions as soon as possible AND remove carbon from the atmosphere in order to meet the targets in the Paris Accord1. The building industry is now tasked with doing “more good” by reducing net emissions to zero and actively contributing to carbon drawdown.
Fortunately, there is a clear roadmap for the building sector to move from being a leading cause of climate change to becoming a key part of the solution. Unlike many sectors, climate change does not force builders to face an existential crisis because it is possible for buildings to become a climate positive industry.
The starting place on the roadmap is for all designers and builders to understand the nature of the issue. Collectively, we’ve done excellent work to address the operational emissions from buildings and have helped move the bar on better codes and created a proliferation of voluntary systems to achieve near zero emissions from high performing new buildings and renovations.
But operational emissions are only part of the problem. A building that achieves zero emissions during its operation is an important step. The other half of the problem now needs to be addressed: material-related emissions.
By recent estimates, the production of building materials accounts for approximately 21% of all emissions globally. We cannot adequately address climate change through operational improvements alone; we cannot “net zero” our way out of this. The “embodied carbon” side of the equation needs equivalent focus and action. We need to take responsibility for all the emissions we cause through harvesting, manufacturing, transporting and installing building materials because of the sheer scale of these emissions.
Tackling these “material emissions” may be easier than you think. The data and tools available to make carbon-smart materials choices is growing rapidly and the evidence of the emission reductions that can be achieved is encouraging.
In a study I completed in 2019, a small (930 m2) multi-unit residential building was modelled with a range of different materials that are all comparable in terms of code compliance, cost and practicality. Material selection was found to have a remarkably broad range of potential results (See graphic top of page 59).
The model with the worst results was responsible for over 240 kg of emissions per square metre of floor area. There is no way that climate change is going to be adequately addressed if new buildings are adding emissions to the atmosphere at that rate.
Some simple material swapping reduced this carbon footprint by over 60%, getting it down to 90 kgCO2e/m2. This is an excellent example of our ability to do “less bad,” and to do so with minimal effort and no undue cost or scheduling issues.
But we can do better. A model for doing “more good” also emerged from the study. It resulted in no net emissions from its materials, but instead recorded a small amount of net carbon storage. At the end of construction of this building, there would be less CO2 in the atmosphere than before it was built.
How is it possible for a building to have net carbon storage? To get to the answer, we need to understand a bit about the global carbon cycle. Every year, the earth’s plants draw down billions of tonnes of CO2 from the atmosphere and through photosynthesis absorb carbon and release oxygen. In a natural cycle, the carbon thus stored in plants is released back to the atmosphere when the plants die and decompose or burn. (See graphic next page.)
Builders can interrupt this carbon cycle by taking carbon-rich plant material and locking it up in buildings, preventing its return to the atmosphere for the lifespan of the building. We have been doing this unintentionally for millennia, incorporating wood and other biofibers into buildings. Conventional building practices include a range of widely available and affordable plant-fiber materials, including products like cellulose insulation, wood fiberboard and many kinds of timber products. By combining these carbon-storing materials with other low-emission materials, results like the 11 kg/m2 of net stored CO2 from the MURB study are entirely feasible with no disruption to the design process, supply chain or construction methodologies.
The use of biogenic materials in buildings can be increased and our carbon positive impact on the climate further improved. There are biogenic material options for every part of a building’s enclosure and finishes. By intentionally choosing appropriate biogenic materials, the amount of net carbon can be amplified so that buildings can actually become a measurable carbon sink on the planet.
The final model in the study (graphic top right) used this approach and was able to offer over 130 kg of net CO2 storage per square metre. None of the materials used in this model are unattainable and all can (and have) met Canadian building code requirements, but many of these are unconventional materials and not currently available through typical supply chains. There is work to be done to make this kind of change, but the result would be a construction industry that actually helps the climate to heal.
Chris Magwood is a director at The Endeavour Centre in Peterborough, ON, which offers two full-time, certificate programs: Sustainable New Construction and Sustainable Renovations and hosts many hands-on workshops annually.
Hi Chris, I enjoyed your article and would like to update you on some significant changes related to closed cell spray foam. It is true that spray foam and other insulation types, such as XPS, that use a HFC blowing agent, have high GWP or carbon footprint. The new versions of spray foam that use a HFO blowing agent have a GWP that is approx 80% less than HFC types. In addition, these new versions (BASF WALLTITE CM01) have a GWP that is appprox 50% of the GWP of products percived as being sustainable.
The good news is that HFC blowing agent foams will be banned in Canada as of January 1, 2021 and products that use HFO blowing agents will replace them. Please consider including information about this in future papers and let me know if you would like me to send you some additional information.