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

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.

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This is an important topic. I would emphasize converting steel production from coal and gas to low emission electricity, either using electric arc furnaces or electrolysis. And reshoring that production from China and elsewhere. Yes, the steel would be more expensive until mass production can ramp up adequately, but then you're employing Canadian workers who pay taxes and buy stuff they wouldn't without employment in the green steel sector.

It's not just about materials either. One has to look at urban design and architecture as well. The Passive House model is an answer to super energy efficient buildings and they can be precision mass produced in factories under controlled conditions, trucked to the site in segments, and put together quickly, like a kit. Passive houses and similar buildings do not spend a lot of time being exposed to the elements while under construction. Multi-family apartments have fewer surfaces exposed to the outdoors and are therein more efficient to heat and cool than single family detached homes.

One can only hope that our cities will one day break their resistance to fee simple, freehold rowhouses and townhouses, essentially ATTACHED single family homes. It stands to reason that row houses can maintain freehold ownership and not be subject to strata title if some basic key criteria are met, such as no shared load bearing walls or underground services, no common property with the neighbours and the privacy, fire resistance and sound attenuation features are codified. Look to the commercial sector on streets with continuous sidewalk retail for a model. Stand alone commercial buildings are commonly built with a small gap between separate load bearing walls. Why can't the same apply to rowhouses or side-by-side non-strata townhouses?

In regard to recycling, yes it's possible to dismantle and recycle existing materials in older buildings, but that adds significantly to the cost of housing in many cities that already have an affordability challenge. Nonetheless, anti-demolition / pro-recycling rules are getting stronger in cities that are severely challenged to also build more affordable housing.

This is where a city can and should do more. If a builder or a home owner wants to subdivide or add infill that will require removal of an existing structure, then, based on an assessment, a city could bend the floor area and/or lot coverage zoning bylaw requirements to allow more square footage in units, or possibly allow an extra unit to offset the builder's cost of recycling vs. far cheaper demolition and landfilling of existing structures. This will require a change in zoning to Comprehensive Development which allows more flexibility. Intelligent and reasonable oversight are necessary, of course, and CD zoning could be subject to vocal opposition by the neighbours. Maybe these are risks worth taking because the results would benefit everyone.

Is maximum floor area a real thing? It seems unlikely that it exists in Toronto, looking at some of the Monster Homes built recently, some of them taking in what used to be a multiple residence footprint.
Passive buildings depend on access to sun. That's not available with really dense building, absent planning that specifically provides for it. One tall building destroys any capacity for growing food on several properties around it.
There needs to be ready access to outdoor spaces: plenty of people just can't get to places out of the immediate neighbourhood.
Something also needs to be done about the toxic laundry exhaust near to ground level in those big apartment blocks. My personal recommendation would be disallowing sale of those products. Can't tell you how many people I've known with asthma and/or eczema, who'll say, "I *love* my ~~~~ (insert name of popular fabric softeners)," not even dreaming it might be the cause of their ailments, and their kids' trouble learning.

I lived in a small row house (c. 1890) in Toronto for many years and couldn't agree more.

Operational emissions are not “looking good”. In TorontoIt’s about 50% of emissions. We are not on a path to reducing that by 50% by 2030. That needs to be addressed.

Embodies carbon is important (though a lot of emission go into building roads, not buildings), we are going to hit our ecological limits for all materials, bamboo included. The reuse of materials is worthwhile research, but is not a cheap or easy path. Reusing buildings as a whole and adapting them to new uses is the most economical. Right now, in Toronto at least, we are knocking down mid.size buildings to build bigger ones, and protect the low rise neighbourhoods.

The elephant in the room is growth. No, we can’t keep growing our population and our cities at the same rate of consumption per person simply by switching materials. The math will not work.

There's a good argument to be made for limiting populations of specific urban areas.
But the matter of world population is looking after itself. Look up "Hans Rosling" on YouTube, to understand why. Hint: it doesn't depend on famine, flood and disease decimating populations in given areas.
The wonderful thing about bamboo is it can be grown densely; but just as with softwood lumber, its strength might depend on growing conditions -- the "re-forested" single species plantations reach mature size quickly, at the expense of density of the wood itself, which determines the strength.
At this point, we should probably have a complete moratorium on clearcutting and renewal or new timber-harvesting licenses, along with a mixed-species replanting requirement that doesn't mean you can go back and cut again when the "wood patch" matures, to make forests carbon sinks once again.
The removal of plastics and petroleum-based adhesives would also make for healthier homes, and lower healthcare costs.
When people stop having any children at all, there are other problems, including who cares for them as they age.
That, too, is looking at "the past."