To build greener buildings, look to the past

Steel, cement and plastic are just a few of the carbon-intensive materials used to create the homes people live in and the buildings that populate skylines across the world. But it hasn’t always been that way, and experts say we can take lessons from the past to decarbonize today’s building sector.

On Tuesday, the United Nations Environment Program and the Yale Center for Ecosystems and Architecture put out a new report, Building Materials and the Climate: Constructing a New Future. In it, the authors say governments across the world need to decarbonize building materials for the sector to reach net-zero emissions by 2050. While materials like steel rely on coal, and cement manufacturers doubled their carbon dioxide emissions over the past two decades, materials like wood and bamboo sequester carbon.

“The shift to biobased materials may seem daunting, but up until the mid-20th century, the vast majority of building materials were locally sourced, low-carbon and specifically designed with climate conditions in mind,” reads the report.

The new analysis follows a 2022 report released by the UN, which found the building and construction sector’s carbon emissions had reached an all-time high.

According to the International Energy Agency, direct emissions from buildings (heating, cooling and electricity use) make up over 26 per cent of global energy-related emissions. Most climate action for buildings targets those emissions and leave out much-needed action to draw down “embodied carbon” emissions from the full life cycle of materials used to create buildings, explained co-author Naomi Keena, an assistant professor at McGill University’s Peter Guo-hua Fu School of Architecture, in an interview with Canada’s National Observer.

“As more and more cities start to decarbonize their grids, then the operational phase will be pretty good if it's relying on clean energy,” said Keena.

“But we still have that problem with the materials. So this is one of the things that we see going forward: that buildings still need to decarbonize their materials if we're going to think about how to decarbonize the whole building sector.”

Around 11 per cent of global emissions come from the embodied sector, which includes the production of building materials such as cement, along with the construction process. The UN report suggests three urgent pathways to reach net-zero emissions for the sector by 2050.

According to Keena, Canada is well positioned to capitalize on those possibilities, the first being to avoid producing building materials to begin with and taking advantage of recycling and repurposing existing products.

The report includes an analysis of Montreal, where the authors looked at the life cycles of materials currently used specifically in residential builds in the city. It considered three scenarios: one, where all the waste from that housing stock went into the landfill when it reached its end of life; two, where there was a mix of recycling and landfill; and three, where everything that could be repurposed for other builds was and the rest went to recycling.

“We found that in Canada, if selective demolition was used in how we deal with our housing at end of life … we could save carbon emissions by 63 per cent as opposed to going to a landfill,” said Keena, noting her report examined housing but the same applies to other buildings as well.

When buildings are demolished, they’re typically broken down into a big pile of debris, which can’t be reused, and Keena says Canadian governments will need to incentivize or mandate contractors to deconstruct buildings. One municipal government in the United States is already making some headway: Portland, Ore., now requires homes built before 1940 to be deconstructed, not demolished. Vancouver has a similar rule, which applies to builds from 1910 and before, along with heritage properties.

Shift and improve

The other two areas the report highlighted are “shift” and “improve,” which refer to changing the types of building materials we use to low-carbon products and reducing the carbon content of conventional materials, such as steel, as we eventually transition away from them.

Bamboo was highlighted as a fast-growing renewable resource: “With a tensile strength close to steel and a compressive strength twice that of concrete, bamboo is used for structural columns and beams, foundation, flooring, roofing and walls,” notes the report.

And while using cleaner building materials is necessary, it won’t happen overnight, and won’t always be viable, said author Barbara Reck, a research scientist with the Yale School of the Environment. She said blending cement with lower-carbon alternatives, using low-carbon sources rather than coal to produce steel, and making production more energy-efficient across the board are ways to reduce emissions from the sector.

As far as Canada goes, Keena said there needs to be a push towards using local low-carbon building materials and a more circular economy-based approach, where materials are reused, repaired and recycled.

“A lot of the building stock in Canada is already built,” said Keena, who said we should think about existing buildings as assets, “banks of material, rather than problems” when considering recycling, building and renovation options.