A proposal to tear down the 25-storey former headquarters of The Toronto Star to build two even larger towers has put the spotlight on climate concepts known as embodied carbon and more sustainable “circular” construction ideas.
Pre-application consultation documents reviewed by The Globe and Mail show Vancouver-based real estate developer Pinnacle International Realty Group is exploring an option to demolish a 53-year-old concrete and glass office building to raise a 90- and 95-storey towers on the same site on Toronto’s waterfront at 1 Yonge St.
But experts say cities are increasingly grappling with the environmental cost of demolishing old buildings particularly as new construction is a major source of new carbon emissions (as much as 10 to 15 per cent of Toronto’s total emissions).
“It takes a lot of emissions to create concrete, to create steel. Those are emitted during the production phase. … It’s really important to prolong the life of materials we’ve created, as we’ve already invested the carbon into those and anything we can do to maximize those materials is a great carbon decision,” said Ryan Zizzo, an engineer and CEO of Mantle Developments, who has consulted with the city on incorporating the concept of embodied carbon into its green development standards he said.
Mantle did a life-cycle assessment case study of six buildings in Toronto, Edmonton and Vancouver and found that retrofitting or building onto existing structures led to 26 to 70 per cent less carbon emissions for the life of the building by 2030 – compared with demolition and new construction – and 11 per cent to 58 per cent by 2050.
He notes that beginning in 2024, New York published guidelines for “Circularity Audits” that review existing buildings for potential adaptation and reuse, and in 2020 the European Union began piloting such audits in a seven cities.
The Residences of 488 University Avenue.Amexon Developments
In Toronto, Mr. Zizzo says, an example of adapting an older building into a new taller structure can be found at The Residences of 488 University Avenue, where Joseph Azouri’s Amexon Developments took an existing 18-storey office tower built in 1968 and added 37 more floors on top, creating a new 55-storey building with residential condominiums.
The height of the new buildings also ties into the carbon discussion, according to Kelly Alvarez Doran an adjunct professor of architecture at the University of Toronto and CEO of Half Climate Design.
“We need to build more housing and we have to address the climate crisis,” Mr. Alvarez Doran said. “New super-tall buildings are absolutely not the right thing to do from the climate perspective. There’s a few studies out there that show that over a certain threshold – over 40 storeys – it really gets more carbon intensive. You get so much lateral force due to wind loads that you add so much more [carbon-intensive] material to the base, so there’s a diminishing return over a certain height.”
A study into different building types, by planning and architecture professors James Helal, André Stephan and Robert H. Crawford, suggests making such tall structures slimmer actually increases the carbon emissions, because of the materials needed to support taller heights. Residensity: A Carbon Analysis of Residential Typologies, a book published in 2022 by Adrian Smith + Gordon Gill Architecture, presented research that showed the carbon emissions necessary to build super-tall buildings are double that required for high-rise or mid-rise buildings.
“Tearing down a 50-year old 25-storey building only to build 100 storeys is basically building 75 storeys at the embodied carbon of 125,” said Mr. Alvarez Doran
Mr. Alverez Doran argues the economic distortions of restrictive zoning contribute to islands of superdensity amid an ocean of low-rise housing as seen in Toronto’s infamous “Yellowbelt.”
“If land value was tied to emissions, we wouldn’t do this,” he said. “We don’t have the incentives to push that density further out, so we end up with tall buildings replacing tall buildings. Why are we taking down 25 storeys, when that density you’re trying to add, it might want to be somewhere else?”
Even if you set aside carbon questions, Mr. Zizzo notes there can be construction cost and timing benefits to reuse.
“Often there’s a little bit more upfront design cost, but I think it can be cheaper because you don’t have to pay for demolition or the new materials,” even the permitting and construction process can end up being faster he said.
“We’re not getting rid of these buildings because they are structurally unfit,” Mr. Zizzo said. “It just needs a little bit more innovation and thinking instead of the lazy approach.”