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Subterranean millionaires. This is what it’s come to in Toronto’s wildly unbalanced and increasingly wacky housing market.

This week Toronto city council adopted a motion introduced by Coun. Jaye Robinson (Ward 15, Don Valley West) to assess the impacts of so-called iceberg houses in the city, “single-family detached dwellings,” the motion reads, “with large, multi-storey underground basements that protrude significantly beyond the surface footprint of the building.”

Essentially, bat-cave mansions for rich people who — having been told they can’t build upward — decide to build multiple storeys deep underground.

Picture a cavernous underground gym, games room, swimming pool and maybe even a lair for an adult child who can’t afford his own above-ground dwelling.

Iceberg homes are the product of “people who want to stay in their neighbourhoods but they can’t build the footprints they want,” says Karen Chapple, inaugural director of the School of Cities at the University of Toronto. “It’s a phenomenon of the superrich and inequality.”

Perhaps you read about iceberg homes in London, England, where for years the massive basements dug out beneath residences in the neighbourhoods of Kensington and Chelsea yielded disastrous results. From the Guardian in 2013: “Excavation work under Goldman Sachs director Christoph Stanger’s mansion has caused shifts in the foundations, forming cracks and trapping neighbouring residents in their flats behind doors that no longer open.”

It’s precisely these kinds of structural and environmental nightmares residents of Toronto’s wealthy Hoggs Hollow neighbourhood want to avoid. Though iceberg houses are uncommon (according to a spokesperson from the Building Industry and Land Development Association), residents of Hoggs Hollow, represented by Robinson, are angry about one iceberg development in particular: a project that according to Robinson will boast “an extended underground basement that includes a multi-car garage and sports court.”

According to Robinson’s motion, the project’s approval by the committee of adjustment, “resulted in the loss of nine trees, including a mature sugar maple tree estimated to be roughly 250 years old.”

Residents are not only angry about the felled tree, they’re worried such a deep build will be vulnerable to major flooding, especially in a flood-prone region like Hoggs Hollow. It’s a valid concern.

“Building deeper underground may destabilize the ground during construction,” says Phil Pothen, of the Canadian environmental organization, Environmental Defence. The risk with iceberg houses, says Pothen, is that “what looks like soil on the surface is actually impermeable concrete. When you get a few feet down all of the water that should be percolated can’t be absorbed. It pools on the surface causing flooding in the neighbourhood, running out into the street, into neighbours’ property.”

What’s more, according to a recent paper by U of T researchers, concrete basements are a leading driver of material use. In other words, if a builder wants to reduce their carbon footprint, they should scrap the basement from their plans — and they should certainly scrap a sprawling luxury basement.

“Single-family ‘iceberg houses’ aren’t providing additional density, and the environmental impacts are well-documented in other jurisdictions,” Robinson told the Star this week.

“We should be applying an environmental lens to all new builds.”

Indeed, we should. In fact, we should be applying an environmental lens to everything in Toronto if we want to prepare the city for the devastation of climate change.

But something city councillors and tree-hugging residents everywhere in Toronto might want to consider is that applying an environmental lens to new builds means more than taking issue with mansions built deep underground. It means saying yes to affordable and modular housing built high into the sky. It means saying yes to subdividing large, single-family homes into several units and welcoming the people who move into them.

It means saying yes more often than saying no.

In Pothen’s view, barriers to intensification and density are a much bigger threat to Toronto’s environment than a bizarre phenomenon like iceberg houses.

“The biggest issue is that Toronto has created a situation where it’s easier on a given piece of land to build one 3,000-square-foot house than it is to build three or four 1,000-square-foot houses. So each of the homes that isn’t being built here [in the city] is being built farther out where people are dependent on cars.

“If we’re going to be allowing environmental impact we should be maximizing zoning rather than blowing it on someone’s fantasy McMansion.

“NIMBYism in Toronto, and sprawl in the greater Golden Horseshoe are two sides of the same coin. If you care about protecting farmland, natural heritage and tackling climate change, you have got to show up in support of intensification in your neighbourhood.”

In other words, go ahead and say no to bat-cave millionaires. Say no to chopping down mature trees in the service of a subterranean sports car stable.

But if you really want to benefit Toronto’s environment, be prepared to say yes to more neighbours — lots of them — below you, beside you and above you.

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