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A rendering provided by Sidewalk Labs shows a courtyard, part of a proposed redevelopment of Toronto's downtown waterfront.Supplied/Reuters

Karim Khalifa wants to show me some nuts and bolts. “Do you know what a rabbet joint is?” asks the director of building innovation at Sidewalk Labs. As he speaks, he unscrews a piece of hardware holding together two huge chunks of laminated Douglas fir.

A rabbet joint, it turns out, is a channel cut into a piece of wood – into which you can insert some hardware to hold a structure together. We’re in the company’s Toronto office, where their vision of an all-wood neighbourhood is being demonstrated with an assembly glue-laminated wood and mass plywood panel. More than a set of pretty drawings, it’s real.

Or is it? The Google sister company’s effort to build an entire urban neighbourhood out of “mass timber,” or engineered wood products, has been inching closer to reality since it was announced two years ago. But there are basic questions still to be resolved, and the end result – while interesting – will be much more prosaic than the marketing suggests.

Wood is a central part of the Sidewalk Labs pitch in Toronto. The company’s effort to build an innovative urban neighbourhood has faced all sorts of complications; in particular, its ambitions to use “urban data” have raised privacy and intellectual property concerns. Wood buildings, on the other hand, are easy to love.

So Sidewalk is shouting “Timber!” It wants to build about six million square feet of offices, homes and retail space, using engineered wood components that have been precut and partly assembled in a factory that Sidewalk promises to build in the area. “Wood is efficient to ship,” Khalifa says, “and quite easy to manipulate with machinery and, especially in today’s world, with robotics.”

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Wooden columns and beams are one of the innovative design and building features of the proposed Quayside development.Fred Lum

It’s an exciting and ambitious vision. But it rests on a large assumption: that Sidewalk, essentially a startup company, is able to quickly design and build a production line that works technically and economically.

If it succeeds, the promised gains are considerable. First, sustainability: Wood is far less carbon-intensive than steel or concrete. Second, it looks amazing. And third, it could be cheaper to produce.

There’s little debate about the first point. But the second and third come with big question marks.

First: what you’ll see. The handsome drawings Sidewalk has released of its proposed new neighbourhoods by Heatherwick Studio – purely conceptual – show a woodsy paradise, mid-rise treehouses with wooden beams crisscrossing above a sunny street and balconies in which fingers of timber reach up to embrace their inhabitants.

This is almost certainly a fantasy. Wood does not do well when exposed to the elements, particular in a climate as prone to extremes as Toronto. This is especially true for softwoods such as pine and Douglas fir, which are inexpensive and from which mass timber is predominantly made.

Khalifa is willing to admit to some spin. “All renderings are sexier than the reality,” he says with a grin, “and I’m not saying we aren’t taking part in that.” Those Heatherwick drawings could be realized, he suggests, with a mix of hardwood. The balconies could be made of Accoya, a commercially available product made from softwoods that are chemically treated. “Would we actually end up building as much as is shown there?” he asks rhetorically. “Probably not.”

If you dig into the company’s more detailed plans – not included in the 1,500-page printed version that it released in June – they suggest this prosaic reality. Three architecture firms, Heatherwick, Snohetta and Michael Green Architecture, designed out what the first piece of the development would look like.

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The columns and beams of the main floor are designed for a ten-storey structure. As the floors rise, the columns and beams would get smaller as there would be less load on them.Fred Lum

The proposal from MGA, which has by far the most experience building with mass timber, actually puts much of the wood behind glass. Mass timber columns rise up from the ground, and after about 10 feet or three metres, are partly sheltered by a glass curtain wall. “We’ve left the wood exposed where we can reach it,” Khalifa says. That’s important, because wood will probably need to be sanded and refinished every three to five years.

Such details matter. Russell Acton, a Vancouver architect whose firm Acton Ostry has been a pioneer in mass timber, suggests Sidewalk and its consultants haven’t yet resolved the details of production and building maintenance. “If they get down to those tough decisions about detail and operations budgets,” he says, “they may find it doesn’t work so well.”

Khalifa rejects that suggestion. “We have an excellent team of engineers, architects, cost consultants,” he says, “and we’re confident that we can solve these problems.” In other words, there’s work that they aren’t releasing to the public.

Fair enough. But the multifaceted Sidewalk Labs proposal has been in the works for two years now, and yet – despite releasing a forest’s worth of verbose and vague documents – they haven’t yet put forward the kinds of detailed drawings that allow their proposed buildings to be scrutinized in detail.

The same vagueness applies to the numbers. As with any idea in architecture, their mass-timber-prefab thesis has to work both technically and commercially to have an impact. Sidewalk’s dual promise was to create buildings that are both very tall and cheaper than other means of construction – and, so, to create a market in North America for mass timber, and to produce “value” that will subsidize affordable housing.

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Sidewalk Labs hopes to achieve economies of scale in its own mass timber factory, reducing the cost of the material, which is more expensive than steel or concrete.Fred Lum

But what will mass timber cost? Khalifa acknowledges that mass timber construction is currently more expensive than steel or concrete structure. But the company’s stated promise is that with economies of scale in Sidewalk’s own factory, this will change.

Thus Sidewalk says it needs approval to build about six million square feet of buildings in mass timber. That’s more than double what they were asked to do by the government agency Waterfront Toronto. Wood, and its economics, are baked into the plan. And the economics of that plan are murky.

If this sounds complicated, it is. Architecture is never only about aesthetics; it’s also about business and science and politics. The very complexity of the Sidewalk Toronto proposal, including its tech and regulatory aspects, turns the usual puzzle of development into five-dimensional chess.

Which means, I think, that it’s a mistake to focus too closely on the nuts and bolts I saw this week. Mass timber holds much promise, and Sidewalk has hired some brilliant architects to take advantage of its possibilities. But what they’ll actually build is another question: one that’s exciting but, as yet, unresolved.

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