The City of Nelson has published a guide for home builders to help them choose low-carbon construction materials.
“Its author, the City’s Climate Resilience Planner Natalie Douglas, says using low-carbon building materials to build highly energy-efficient homes could result in substantial greenhouse gas emissions reductions
But how to do this, and what materials to use, is an emerging science.
After a year of research, the city’s Material Carbon Emissions Guide came out in March, accompanied by another document, the Benchmarking Report. Douglas presented them to council at its May 24 meeting.
“This is novel and timely work,” she said. “We are one of only a handful of Canadian communities that have conducted localized embodied carbon research. This is a topic that is already transforming the building industry.”
The guidebooks are intended to help builders and the city grapple with the problem of embodied carbon – the greenhouse gas emissions arising from the extraction and manufacturing of building materials such as concrete, foam insulation and steel.
The conventional way to measure the carbon footprint of a building is to analyze its energy efficiency after it is built and is lived in. Those emissions, created by the heat that leaks through the building envelope, are known as operational carbon emissions.
But counting those emissions misses the significant footprint in the building materials, or embodied carbon emissions.
Nelson Next, the city’s climate plan, names low embodied carbon in buildings as a priority. Douglas’s work is managed by the City of Nelson and funded by FortisBC.
The Benchmarking Report contains the results of work done last year by Douglas.
She analyzed the amount of embodied carbon in 34 houses in Nelson and Castlegar, concluding that these homes had, on average, 28.8 tonnes of embodied carbon emissions associated with the build before anyone had even lived in the home.
The study highlighted some of the highest carbon-emitting building materials based on data from the 34 houses. These included various kinds of concrete, insulation and exterior cladding. The results also include details on alternate types of concrete, insulation and cladding that have lower footprints.
The work was done using a specialized tool developed by the group Builders for Climate Action in Ontario.
The Benchmarking report can be found at https://bit.ly/38Eum8J.
Material Carbon Emissions Guide
The Material Carbon Emissions Guide contains new work completed since the fall.
It offers an analysis of eight materials: concrete, insulation, cladding, interior surfaces, windows, framing, roofing, and structural elements (steel and wood posts and beams).
Of those materials, concrete accounts for the highest total average material carbon emissions per house at 35 per cent, based on the homes in the study. The majority of the emissions associated with concrete comes from the production of one of its main ingredients, cement. The report gives details on the emissions attached to different types of cement, including alternative lower carbon types.
Similar analyses are applied to the other seven material types listed above, with product rankings.
Douglas told council that, in writing the report, she engaged with about 50 builders and other building professionals in Castlegar and Nelson in the fall of last year, “and we had a great response, they responded with intrigue and enthusiasm.”
Douglas said the two publications are already being used by other municipalities.
“It’s been really exciting to see our content actually being used beyond Nelson,” she said, adding that the provinces and the federal government could one day regulate embodied carbon as a method of substantially reducing emissions.
“Getting ahead of it is really good for our building community,” she said.
Douglas explained that embodied carbon emissions can be calculated before construction of a building. Using an example of a house with 28 tonnes of embodied carbon, she said her work shows that it would take 23 years of operational carbon emissions to equal that 28 tonnes.
“By focusing on high-emission and high-volume materials, we really can make significant reductions today. Some builders in our community are already doing this. I am obviously a keener and a nerd on this, but it is great to know that I am not the only one.”
The emissions guide can be found at https://bit.ly/3MdAthL.
At the May 23 meeting, Councillor Jesse Woodward, referring to this embodied carbon work and a presentation at the same meeting about Nelson’s collaboration with UBC to evaluate the cost-effectiveness of promoting e-bikes as a climate solution, said, “I am in awe that this is happening, at such a refined level, that we have people digging into this. As one city, the impact would be negligible, but if 1,000 towns were doing this kind of work, it is really powerful.”