Canada’s housing crisis stems from two major gaps: affordability and supply. The prevailing wisdom is that we can build our way out of both. The logic of the Carney government’s Build Canada Homes, for example, is to increase supply to make housing more affordable. But what about the homes we already have?

As architects and principals at ERA Architects, my colleague Graeme Stewart and I have spent years studying the apartment buildings that reshaped Canadian cities in the decades after World War II. The population increased dramatically during this period as veterans returned home, baby boomers were born and millions of immigrants arrived. The government’s response to the resulting housing shortage was to expand its role in the market through the Central Mortgage and Housing Corporation, offering mortgage insurance and low-cost loans to reduce risk and spur large-scale residential construction. In the 1950s, ’60s, and ’70s, Canada built its way out of a looming housing crisis. Thousands of apartment towers rose across the country, many developed by the private sector with public financing. Now, more than half a century later, those homes are aging out.

For one thing, their insulation and ventilation systems are no match for Canada’s new climate. Many are heated through gas furnaces—dating back to a time when gas was affordable—and insulated to far lower standards than today. Summers were cool enough that we didn’t need air conditioning. But extreme weather is now a part of daily life. This July, Toronto experienced some of its worst air quality in recent memory as smoke from northern wildfires drifted south. If someone is living in an older, poorly ventilated apartment and can’t open their window on a hot day because of the toxic outdoor air, they’ll overheat. In the winter, a lack of insulation can make homes a lot more expensive and carbon-intensive to heat, while the disparity between indoor and outdoor temperatures creates condensation on windows that later leads to dampness and mold. All of these inconveniences reduce overall quality of life over time. In the Greater Toronto Area alone, we have a million people living in high-rise housing in need of modernization.