Newest towers will give S.F. skyline a touch of glass
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Newest towers will give S.F. skyline a touch of glass
John King, Chronicle Urban Design Writer
Monday, November 26, 2007
Architecture has its trends like any other field of design - and in San Francisco, today's changing skyline shows that the glass box is back.
Six sleek towers are under construction, and several more have been approved or proposed. Some are reflective; others offer a voyeuristic peek inside. The colors range from icy blue to smoky green.
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The city planners who approved these translucent high-rises already are having second thoughts, emphasizing that glass towers need to remain the exception, not the rule. But architects say glass is in sync with today's world, a symbol of contemporary life as well as technological innovation.
"In this day and age, society wants to be more transparent," said Ali Moghaddasi of HOK architects, the designer of a recently approved 27-story glass tower near First and Mission streets down the block from 555 Mission St., a glass high-rise that opens next year. "Look at the Internet, where information is free and available to everyone."
Instead of the masonry-clad structures that define other eras, San Francisco's new crop includes the soon-to-open InterContinental Hotel at Fifth and Howard streets. A cross between a glacier and an old-fashioned apartment radiator, the curvy inn's hue is so vivid that it's being marketed as "32 stories of cool blue luxury in the heart of San Francisco."
"I wanted a look that would be fluid, close to water," said designer Alberto Bertoli of Patri Merker Architects. "San Francisco's urban form is kind of sad-looking, solids and concrete or stone."
Five blocks to the east, the milky blue Millennium Tower at 301 Mission St. is not so much a glowing object as a chameleon - a 60-story shaft where the glass serves as a canvas behind thin steel fins that form a diagonal streak sliding up and around the tower's four sides. Viewed straight on, the fins disappear. At an angle, they're as vivid as the mark of Zorro.
"The idea was to create a fragmented crystal with striations that keep shifting," said Glenn Rescalvo of Handel Architects, the designer. "It's more about the shape of the building than the color of the glass."
The difference in these two "blue" buildings shows the design possibilities of glass, which can be manufactured in hundreds of fine-tuned variations. At the InterContinental, the glass lets in 71 percent of daylight and has a "reflectance factor" of only 7 percent, meaning that very little light bounces off. By contrast, 301 Mission's glass repels more of the light that hits it, increasing the mirrored effect.
Aesthetics aren't the only factor that architects take into account when selecting glass.
San Francisco's City Planning Department wants glass towers to be as transparent as possible, fearing that shiny or mirrored buildings might stick out like glitzy thumbs. But ultraclear panels allow unfiltered sun into a building, driving up energy costs because of heat gain and the need for air conditioning. That runs against state mandates on the use of energy as well as the city's desire for buildings that meet high environmental standards.
Glass can be tinted to reduce the heat gain or sprayed with a metallic coating, but then the result can be too dark or too slick.
So architects do a juggling act, helped by manufacturers offering new "blends" that balance transparency and performance.
"Glass is changing rapidly because the demands on the glass companies are changing rapidly," said Jeffrey Heller of Heller Manus Architects, whose firm is on the design teams of several towers. "Sustainability is coming on like a rocket ship."
San Francisco planners face a different challenge: making sure the new skyline doesn't look like it parachuted in from Dallas.
That wasn't a concern when today's towers were on the drawing board. Then, they were a welcome contrast. Millennium Tower sits amid stone-clad towers from the 1980s. As for the InterContinental, "We were really tired of beige precast concrete panels with green-glass windows," said Craig Nikitas, a senior planner with the city. "To get something with its own integrated color seemed like a nice change."
To be sure, glass-clad buildings are nothing new in San Francisco. The Hallidie Building, built at 130 Sutter St. in 1917, wears one of the world's first glass "curtain walls," in which pre-assembled panels are hung into place on a building's structural form.
But as glass-and-steel high-rises recast the skyline after World War II, overtly modern buildings sparked a backlash. The shift culminated in 1985's Downtown Plan, which decreed that new buildings should "contribute to the visual unity of the city." Another rule: "Highly reflective materials, particularly mirrored or highly reflective glass, should not be used."
The planning director at the time: Dean Macris. The planning director today: Macris, who returned to the post in 2004.
While Macris now champions contemporary design, he and Nikitas say the 1985 edict against glossy glass still applies. But the sheer number of sheer towers is causing alarm, as is the fact that the first batch hasn't lived up to planner expectations: "I can't say we've said, 'Aha, there's the perfect solution,' " Macris admitted.
Concern reached such a point this summer that planners almost proposed changing the city's zoning codes to define exactly what percentages of reflectivity and transparency would be allowed. Instead, the department will work to strike a balance case by case, allowing fresh styles but seeking to prevent skyline-marring mistakes.
"Our job is to take the collective view," Macris said. "This city is so overwhelmingly masonry, the balance won't be tipped by the latest crop. But we could be at a point south of Market Street where we encourage the next set of guys to come in with something other than all-glass facades."
In the case of Moghaddasi's Mission Street tower, which will have a tapering shape the architect likens to "a diaphanous candlestick," Macris and Nikitas worried that the wall samples had too green a tint. So they visited a manufacturing yard in Alameda to see a sample wall panel measuring 10 by 13 feet.
"This is an art, not a science," said Macris, who decided the glass passed muster. "We're trying to do our best between all these competing objectives."
On SFGate.com: John King gives a tour of San Francisco's glassy new skyline (Video): http://www.sfgate.com/cgi-bin/object...0SKN52.DTL&o=0
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E-mail John King at jking@sfchronicle.com.
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http://sfgate.com/cgi-bin/article.cg.../MN00SKN52.DTL
Note the bit about the green tint of the glass on 535 Mission--I'm jazzed with anticipation of that.
Last edited by BTinSF; Nov 27, 2007 at 12:06 AM.
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