2025, Toronto
Toronto Tower Demo: High Carbon Sites
Mapping the environmental impacts of large-scale demolition
Understanding The Problem
While demolition has been a prevalent part of North American city-building since the mid-century, in the last decade we’ve seen a significant increase in the demolition of large-scale buildings. In Toronto, the city is witnessing demolition proposals for numerous 10+ storey urban towers. And this large scale of building waste increases when including the many buildings experiencing 85% demolition as part of the rise of facadism. This premature loss of towers results in “high-carbon sites”, raising significant environmental sustainability concerns, as well as concern for the concept of heritage value as we begin to lose our mid-late-century architecture before it has a chance to be called “heritage”.
Over the last decade, there has also been a focus in the city-building industry on sustainability initiatives such as net-zero targets, specifically improving the operational energy of the new buildings replacing those demolished. However, significantly less focus has been placed on embodied carbon, landfill waste, and the relationship of this successive demolition-development cycle in relation to the climate crisis.
What has led to this creation of the “high-carbon site” in Toronto? One significant factor is rigid and restrictive land use policies – the “yellowbelt” zoning of the city excludes single family home neighbourhoods from new higher-density development, forcing housing development pressure into a relatively small and historically significant part of the city.
To bring attention to this, Giaimo has started mapping large scale demolition in Toronto: see map here. For smaller scale demolition and redevelopment that leads to site intensification, solutions such as deconstruction and material salvage can be explored; however, the large scale of tower demolition is especially problematic, as demolition of just one tower is equivalent to many hundreds of “typical houses” in Toronto.
By undertaking a high-level embodied carbon analysis of these proposed demolitions and redevelopments, we have found that not only does tower demolition result in substantial landfill waste, but the new construction buildings replacing the existing towers have an incredibly high carbon footprint compared to other typical building types.
For example, using 25 St. Mary Street as a case study, the scale of demolition of this 24-storey building is equivalent to the waste produced by the demolition of 640 “typical houses,” while the site area is only the footprint of 23 average “house sites”. If we consider the upfront carbon of the new developments as the total carbon of the new construction AND the lost embodied carbon of the existing building being demolished, the total upfront carbon is incredibly high at 56 million kg CO2e. While the new development does increase the number of residential units on the site, the carbon footprint of each individual unit is over 3 times higher than the carbon footprint of a “typical house” in Toronto. If this project was allowed to be built in the site of 23 houses, instead of demolishing a 24-storey tower, there would be a 30% carbon reduction. Despite the appearance of our industry becoming “greener”, we’ve managed to allow for the development of the highest-carbon footprint possible for a single residential unit.
What can we do?
By understanding the significant environmental damage this is causing, we can better inform future policies around demolition, circularity, reuse, decarbonization, and embodied carbon. Giaimo also works with property owners to develop more resilient solutions for their existing buildings through adaptive reuse, retrofits, and restoration; with rising construction costs, reuse is not only an environmentally sustainable approach, but also financially sustainable. We also need to recognize that Toronto is growing, more housing is needed, and thus there is a need to reform our current zoning and land-use planning policies which unintentionally contribute to encouraging demolition and redevelopment of towers.
While this research focuses on environmental concerns, there are also negative impacts from a social and cultural perspective. A number of the towers being demolished are apartment buildings, displacing hundreds of tenants during a housing crisis. Groups such as No Demovictions are doing important advocacy work to this end: “at a time when we need more housing, not less, it is vital to grow rather than destroy the stock of affordable housing. While in many cases demovictions will build more units in the re-development, it is also removing up to 5,000 units of housing at the same time. With a vacancy rate of 1.7%, tenants are being displaced and forced to fight their neighbours for a very limited number of rental units in their price range.”
Ongoing Research
This research builds off sustainable reuse ideas already well-established by Canadian researchers and thought-leaders including Waste Heritage by Susan Ross and Upfront Carbon by Lloyd Alter, as well as international movements that embrace a circular economy including the Architects’ Journal RetrofitFirst! Campaign and HouseEurope! initiative advocating for “the Right to Reuse” and renovation over demolition.
While Giaimo continues to develop this research, these preliminary findings were presented by Giaimo Associate Mitchell May at the 2024 joint National Trust for Canada and Association of Preservation Technology Conference in Montreal, and will be discussed at the upcoming To Build Law Screening hosted by Toronto Society of Architects, Canadian Centre for Architecture, and Azure during the panel discussion with Creative Director Stephanie Mah.
Notes on assumptions
Proposed building calculations are based on tall building average of 520 kg CO2e/m2, per research conducted by Ha/f Climate Design in 2023. Proposed below grade parking structures are included in calculations. Existing building calculations are based on CAGBC average for buildings of 400 kg CO2e/m2., from the 2022 Embodied Carbon: A Primer for Buildings in Canada white paper. Existing below grade parking structures being demolished are not included in calculations. Single family house calculations are based on EMBARC study average of 189 kg CO2e/m2 for heated floor area, based on median Toronto house floor area of 141 sq m.
All calculations are high-level estimates to get a snapshot of the larger issue, as opposed to undertaking detailed whole life carbon analysis of each individual property. This research is less of a critique on individual redevelopments or property owners, and more focused on understanding big-picture city-building trends related to land use planning and decarbonization policies in Toronto.
