How dense is too dense?

For city planners and urban designers, that question represents an essential predicament of the times: the challenge of building more compact, green living spaces that don’t swamp infrastructure or sully communities with untenable congestion.

It also reverberates in the debate over the grandiose triple-tower development proposal on King St. W. that’s being pushed by theatre magnate David Mirvish and renowned architect Frank Gehry. Toronto’s chief planner, Jennifer Keesmaat, has expressed “serious concerns” over how the already jam-packed downtown strip can handle an influx of people living in three new 80-storey towers.

“I don’t think we as a city have an obligation to absorb this much density,” she recently told the Star’s Christopher Hume.

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And yet, many agree — including Keesmaat — the city must get denser; the question of how, and how much, is vital to shaping the Toronto of tomorrow.

“There are good ways to do density and there are bad ways to do density, and a big part of the difference is design,” said Keesmaat in an interview Monday, citing access to light, privacy and quality public space as important factors.

“This is a critical question for the city. We need to figure this out, and this is key to the work we’re doing.”

Urban density has become a hot-button issue in cities around the world, particularly as awareness of climate change has amped up pressure to curb the use of fossil fuels, said Tribid Banerjee, chair in urban and regional planning at the University of Southern Californian’s Sol Price School of Public Policy.

There’s a widening consensus among urban planners, Banerjee said, that the postwar suburban boom, wherein the “American Dream” was defined by wide lawns and family drives on open roads, isn’t feasible anymore.

“The urban sprawl has basically become unsustainable,” he said. “The whole issue of global warming and climate change has put a new emphasis on the compact city argument.”

That emphasis has spawned a slew of policy discussions, studies and debates around how best to build 21st century cities. Among the focuses of the field is the balancing act between public and private space, ensuring room for affordable housing and studying the psychological affects of living in closer proximity with one’s neighbours.

Vishaan Chakrabarti, former director of the Manhattan office of New York City planning, believes there’s no prescribed formula for urban density. But he argues in his recently published book, A Country of Cities: A Manifesto for an Urban America, there’s a general sweet spot that should be targeted: 30 dwelling units per acre, which he calculates is just enough to justify building transit such as subways or light rail, so that denser neighbourhoods don’t get clogged by a glut of car traffic.

“It’s not about density for density’s sake,” he said. “I focus on that minimum that you need for that sort of urban condition.”

Part of the challenge, therefore, is ensuring density doesn’t outstrip the capabilities of infrastructure such as transit, sewers and electrical supply. The pace of densification has to take such physical frameworks into account, as well as the “social infrastructure” of schools, hospitals and access to green space, said former Vancouver city planner Larry Beasley.

He said Toronto, with its boom in downtown condo construction, could do better with ensuring new residents have the social and physical amenities that make increased density bearable.

“You haven’t kept up,” he said.

Keesmaat doesn’t take issue with this; hence her focus on increasing Toronto’s density through midrise developments on what she calls “the avenues” — stretches of St. Clair Ave., Bloor St. and others where city planners determine there’s room for more people without straining the existing infrastructure.

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“They can accommodate density in a way that one might argue is much more gentle,” she said.

And when it comes to big-scale projects such as the Mirvish-Gehry proposal, Keesmaat said the city needs get better at making sure public space isn’t compromised as an area becomes more tightly packed.

“I think we’re struggling with this,” she said.

“We’re seeing the density, but I think we’ve yet to master ensuring that we have the spectacular accompanying public realm. And those two things have to go hand in hand.”

Mirvish has argued that replacing the existing warehouse buildings with his project would widen the sidewalk and improve the flow of pedestrian traffic, creating a “cultural corridor” in the entertainment district.

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