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Nearly a third of Canada’s greenhouse gas emissions come from structures we build: houses, commercial buildings and infrastructure.
That’s a good reason to choose building materials with the smallest carbon footprints and to be innovative with materials so that our country can meet its emission reduction targets.
Currently, governments and industry use a tool called a life-cycle assessment (LCA) to measure a building’s carbon footprint. This analyzes greenhouse gas emissions (GHG) from each building component in a structure – the wood, steel, concrete and so on – during each phase of its lifespan.
An LCA would analyze the concrete in your home by adding the estimated carbon emissions created when the concrete was first produced, then adding emissions it releases for as long as your house stands, plus emissions when your home is one day torn down. Then it would analyze your home’s wood. Then the metal…
This analysis tool is influential. It informs Canada’s national building codes as well as some provincial purchasing policies. It is the best tool available for evaluating the GHG performance of alternative building products and designs.
It does have limits. Policymakers, building designers and the public should be aware LCAs have challenges and uncertainties that should be considered if we’re going to reduce our buildings’ carbon emissions.
Policymakers could be misdirected
First, existing LCAs can produce widely different results, even for similar buildings, if people conducting them accept data gaps and use different assumptions.
Second, LCAs tend to discount significant regional differences in the GHG emissions of different materials. For example, wood harvested, manufactured and disposed on the West Coast may have a very different GHG profile than wood on the East Coast. LCAs typically ignore this variability and use average national, continental or global data.
Third, LCAs can exaggerate the importance of one stage of a product by ignoring or discounting other stages. An LCA may emphasize how much carbon a building material stores when it’s produced. That would ignore how much carbon the product gives off when the building is operational, how it impacts the building’s energy efficiency, and how much carbon it emits when it winds up in a landfill.
Used in isolation, these results can lead to decisions that are too narrow in scope, harming chances of taking more comprehensive action on reducing our buildings’ GHG emissions.
These uncertainties and variations are especially significant when considering biogenic carbon – carbon found in our plants, trees and soil. For example, current LCA practices can be uncertain about how much carbon is emitted or stored by wood building products at different stages in their use. A recent IISD study, Emission Omissions: Carbon accounting gaps in the built environment, suggests these omissions could represent up to 72 per cent of total life-cycle emissions.
Despite tremendous progress on building efficiency, our research also suggests operational energy consumption remains the most important source of GHG emissions from a building over its life. For this reason, material choices need to be made on a building-by-building basis. It’s not good enough to pick products by their individual footprints; we need a holistic understanding of the role different materials play enhancing the structure’s “whole life” environmental performance.
Three ideas for a smaller carbon footprint
To ensure Canada’s building sector helps us meet our Paris Agreement goals, there are three recommendations our policymakers and builders should strongly consider.
First, improvements in energy efficiency, durability and developing new low- or net-zero-energy buildings offer the highest GHG mitigation potential. Policymakers should focus on promoting building resilience and longevity paired with deep efficiency improvements.
Second, LCAs remains the right measuring tool, but more data, transparency and robust standards are needed. Policymakers and building professionals looking to decarbonize buildings should use caution when making decisions that prefer one building material over another. Uncertainties, assumptions and omissions in LCA studies – particularly with respect to biogenic carbon – suggest comparisons across building materials are fraught with complexity.
Third, Canada should focus equally on material efficiency and rewarding decarbonization across all material manufacturing sectors. Most Canadian buildings use all three primary building materials (concrete, steel and wood) to some extent. It only makes sense to focus on policies, strategies and technologies that can reward GHG reductions in each building material sector.
Deep emission reductions, on the order of 60 to 80 per cent, are required for Canada to meet its long-range emission reduction targets. For the buildings sector, this will require large-scale investment in new low-carbon technologies and practices.
In the wake of the Canadian government’s report noting rapid temperature rise across our country, the need to look more deeply at building materials as sources of – and solutions to – climate change is clear. Greater transparency and robust standards are needed for our main measurement tool if we are to get decarbonization right.