Noah, Harper, Ava and Michael have typical Canadian childhoods: they hang out at the pizza joint, try not to get kicked out of the swimming pool, get into trouble for trying to smuggle a purloined Barbary sheep into their home. The mountain-bred sheep was an ideal pet, they had thought (though their parents very much disagreed), because they live on the 30th floor of a 47-storey apartment building.

In other words, the characters in Jackie Burns's book, The Condo Kids, are very much part of this country's norm. This generation of Canadian children is growing up in homes with balconies and elevators. Yet, Ms. Burns realized, reality is almost absent from our country's self-identity: Of the thousands of kids' books, she couldn't find one that was set in a home above ground-level.

Apartment-owners, renters and dwellers are already the majority in Montreal and Vancouver – in both cities, more than six in 10 homes are in multiunit buildings – and a plurality in Toronto, where 44 per cent are. And they are growing in number: Between 2001 and 2016, the number of apartment homes in Toronto increased by 180,000, or 40 per cent; in Vancouver by 65,000, or 78 per cent.

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But you wouldn't know it. Canada suffers, almost uniquely in the world, from a priggish middle-class animus against homes in the air. The word "condo" is deployed as a derogatory badge of sterilized and inauthentic living, or wielded as a residential pitchfork by the detached-home elite. In too many Canadian neighbourhoods, multiunit dwellings are viewed as threats to be fought and appealed, not as new neighbours to be welcomed.

In Europe, apartments have long been the middle-class norm. Apartment-dwellers are the majority in Italy, Germany, Switzerland, Greece and Spain (where almost seven in 10 live in an apartment). Most of those apartments are owned by their middle-class residents. More than eight in 10 Spaniards own their dwellings, as do the majority in every country except Switzerland and Germany.

By joining the rest of the world, Canada will improve its ecology, economy and quality of life by filling the empty, inhuman dead spaces that blot its cities with a lot more condo kids.

We need to apartmentize ourselves a lot faster. The price of housing in cities has risen far faster than incomes. Home ownership has been key to the Canadian dream: It is the reason why immigrant integration has succeeded, and why poverty rates have fallen. A shortage of housing supply (both rental and owned) jeopardizes both.

That crisis of supply is rooted in the low population density of large parts of Canada's largest cities. In Toronto, Vancouver and Montreal, there are huge swaths containing only single-family homes, their density too low to support public transportation or full-fledged urban life. Too many Toronto subway stations and Vancouver SkyTrain stations are surrounded, not by dense clusters of apartment housing, but by wasteful low-rise neighbourhoods.

This is changing too slowly: It is far too easy for inefficient, low-density residential districts to oppose or severely delay the addition of apartments into their housing mix. (Ontario this week took a step in the right direction by eliminating the Ontario Municipal Board, which facilitated such appeals). As a result, cities have fallen victim to urban sprawl rather than life-improving density increases.

And the low density of our cities and our fixation on single-family dwellings leads, in turn, to an ecological crisis. Canada's two largest sources of greenhouse-gas emissions are transportation (mainly from private automobiles) and heating (especially from inefficient single-family homes); together they make up almost 40 per cent of our carbon output. New multiunit housing is vastly more energy-efficient than even the greenest single-family homes, and its density makes possible the green transportation systems that our cities are too sparse to support.

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Canada's big cities will at least double their populations this century. If they are to be liveable, pleasant, efficient places, they need to keep that growth within their sensible borders: The Urban Containment Boundary in Vancouver, the Greenbelt in Toronto, the metropolitan boundary in Montreal. As a country, we need to grow up, not grow out. We need to welcome a generation of condo kids.