The Kootenays Low Carbon Homes Pilot highlights importance of embodied carbon

The municipalities of Nelson and Castlegar, BC are positioning themselves as leaders in the realm of embodied carbon research with their recently published Benchmarking Report and Material Carbon Emissions Guide

This March, in partnership with Builders for Climate Action and 3West Building Energy Consultants, the two communities published two groundbreaking reports to support the accounting of embodied carbon in home building as part of a Low Carbon Homes Pilot.

Embodied emissions are a critical component in conducting holistic carbon footprint analyses of new builds. As we revealed through PBC’s EMBARC report, also completed in partnership with Builders for Climate Action, new home builds in the GTHA contain roughly 840,000 tonnes of carbon–equivalent to the emissions from more than 183,000 automobiles.

This new work has been led by Natalie Douglas, Nelson’s Climate Resilience Planner. Douglas told me the communities were motivated to advance embodied carbon accounting out of both interest in moving to require Step 4 of the BC Energy Step Code for Part 9 residential homes (i.e., more stringent energy efficiency requirements), and concern for the significant emissions associated with building materials–especially in highly energy efficient buildings, such as passive houses.

Indeed, their concerns and interests are well matched. As shown in the Benchmarking Report, 70% of dwellings that were above average in material carbon emissions were homes achieving higher energy efficiencies in the BC Energy Step Code (Steps 4 and 5). This is not to say that higher energy efficiency homes inherently have greater carbon footprints; the analysis from Builders for Climate Action is clear that it is the choice of materials that impacts embodied carbon. Regardless, this highlights the importance of this accounting for embodied carbon in designing and regulating new builds and sustainable homes.

The more difficult challenge–but worthwhile–will come with trying to regulate Carbon Use Intensity, one of two key metrics shaping the Benchmarking Report. To understand the carbon emissions of newly built houses operating over time, Carbon Use Intensity is used as it combines material and operational carbon emissions and examines them over a time period. So, CUI30 is the total operating emissions plus material emissions over 30 years.

Material carbon emissions must become a standard consideration if we are to curb the impacts of climate change. Even the most well-intentioned and energy efficient home could take decades of operation to offset the emissions created in making the materials for the home. In the Kootenay study, it was found that it would take 23 years before the cumulative amount of operational emissions associated with an average new home in Nelson or Castlegar would match the current average amount of material carbon emissions at the time of construction. This finding is critical because we have a limited global carbon budget, particularly if we want to limit global warming to 1.5℃, and material carbon emissions enter the atmosphere immediately, as compared to the gradual increase with operational emissions.

Graph comparing material carbon emissions with operational carbon emissions over time, extracted from Benchmarking Report.

The second key metric that Douglas advocates to use is Material Carbon Intensity by Function (specifically, by a function of Density). This additional analysis works to discourage large empty homes and promote other municipal policy goals such as densification. To calculate this, they used: (# bedrooms/house volume in m3) * (1,000/material carbon emissions). Use of the metric is displayed in the figure below.

Comparison of Material Carbon Intensity by Density, extracted from Benchmarking Report.

Similar to PBC’s work through EMBARC, and discussed in detail in the Material Carbon Emissions Guide, they found that in Castlegar and Nelson, concrete, insulation, and cladding are the largest contributors to embodied emissions. Douglas asserted that this knowledge opens up some “quick wins and low-hanging fruit that won’t require much change from standard building practices in Castlegar and Nelson.”

Easy solutions could be choosing “lower carbon concrete mixes and carbon storing insulation types (i.e., cellulose).” For more significant changes, Douglas recommends, and pointing to the “Targeted Insights” section of the Benchmarking Report:

• “Design[ing] homes to minimize concrete with the lowest possible [material carbon emissions];

• Minimiz[ing] the amount of uninhabited floor area by eliminating or reducing the size of garages and unfinished basements;

• Consult[ing] the Material Carbon Emissions Guide to get a general idea of what materials have the most emissions associated with their extraction and manufacturing;

• Consult[ing] [Environmental Production Declarations] where available and advocat[ing] to material manufacturers to produce [them] if they’re not yet available.”

Visualization of embodied carbon emissions by building material type, extracted from Materials Carbon Emissions Guide.

When asked for recommendations for policymakers looking to advance similar work in their communities, Douglas advised, “be willing to fail and learn to do better, [...] collaborate efficiently and compassionately–we can’t wait for perfect.”

Articles on the PBC website reflect the views of the author and not necessarily those of PBC.
Raidin Blue is a summer technical writer for PBC. He earned his MES at York University and B.Sc.Hon. from the University of Saskatchewan.
Cover image: "Nelson" by Steve Schmidt licensed under CC BY 2.0.