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I like the shine, lift and futurism of numerous glazed residential towers that have dotted Toronto's downtown cityscape in recent years.

That's not saying all of these buildings measure up uniformly to high artistic standards. But it is saying that even the less imaginative ones often show what a beautiful, luxe and urbane material contemporary glass has become.

Nor, as I found out a couple of weeks ago, have developers run out of ways to apply glass solutions to the outfitting of high-rise buildings.

Take, for example, what is happening at Sixty Colborne, a glassy new inner-city condominium project by Peter Freed just east of Yonge Street. Four ample units stand at the corners of the complex, each with an area between about 1,000 square feet and 2,000 square feet. (Prices range from just under $705,000 to over $1.4-million.) The problem: At those prices, prospective home-owners would probably want a balcony, and none of the suites has one.

To remedy this lack, Mr. Freed is offering (for about $50,000 on top of the unit price) to modify the glass walls of the suite so they can be slid aside. The result, when the wall is fully open, will be a gap 16 feet wide and extending from floor to ceiling, which should transform a corner of the apartment into a balcony-like space.

This modest move – which I've not seen in high-rises elsewhere – will attractively blur the normally firm line between outside and inside, city and home. With Mr. Freed's innovation in place, house-owners can have the pleasure of a terrace (when they want one) without paying for a balcony they only use a few months of the year.

But despite the facts about its celebrity and versatility – manufacturers are churning out new products all the time, consumer demand for glazed apartments is high, developers and architects continue to come up with interesting things to do with it – glass has been attacked far and wide in recent years.

To cite just one local instance: CBC Toronto's popular Metro Morning website advises us that "building scientists have known for a long time that glass-walled structures are less energy efficient than the stone and concrete buildings that were put up forty or fifty years ago … [I]ndustry insiders warn that as energy costs climb, glass towers may become the 'pariah' buildings of the future."

The same series of witheringly critical articles and broadcasts quotes high-profile researchers who have weighed in against the cladding of tall towers with glass. One of them is Ted Kesik, an engineer and professor of building science at the University of Toronto, who has separately published his findings and remarks on the Web. (His article can be easily located by Googling the author's name.)

The current real-estate boom, Mr. Kesik writes, has created a generation of towers wrapped in glass systems that will probably fail after only "15 to 20 years," and that are, from the outset, "thermally inefficient compared to curtain walls or punched windows."

"There is no villain in this story," he says, but virtually everyone with any connection to the world of real estate – developers, manufacturers, architects, agents, consumers – has "collectively contributed to the present situation." Which, by Mr. Kesik's accounting, is or soon will be a bad situation indeed.

"Preposterous" was the word Peter Clewes used, when I asked him last week to characterize the apocalyptic scenarios sometimes forecast by the anti-glass faction. (Mr. Clewes is the architect of Sixty Colborne and nearly 20 other glass-clad towers in downtown Toronto.)

"Conventional double-glazed units," he said, "whether they are in punched windows in a fancy Rosedale house, or in a cheap, cheap condominium in Scarborough, have a life expectancy of between 35 and 40 years. After 40 years, the seal around the perimeter starts to break down, and you can get some moisture."

Like a roof or floor, "glass has to be ultimately replaced. That has to be built into anyone's maintenance budget," he said.

Mr. Clewes attributes the durability of contemporary glazing systems to industry advances over the past few decades. "We built throwaway buildings in the fifties and sixties, with single-glazed sliding windows that leaked like a sieve. We know how to keep water out now. We have solved the big technical problems. What we are into now is refinement. How far do we want to take energy performance, for instance?"

The answer to that question will be determined by the tolerance and expectations of the marketplace. Mr. Clewes advocates high energy taxing as a proven way to encourage personal conservation and good public policies – and a much more effective way than preaching at people to be "greener."

"Once we stop the moral rhetoric, and start taxing energy," he said, "then we will quickly have a more sustainable city"

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