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Solar Memory

As history shows, harvested daylight is a rich resource on even the most constrained sites

04/2007

C. C. Sullivan

Like the tools used to simulate outdoor light, blue-sky thinking is vital to sustainable building design. Yet capturing useful sunlight is hard enough even when conditions are ideal—new construction on a greenfield site in central Arizona, for example, is as close as one gets to perfect uniformity and consistency. Most situations are far less than perfect, which clouds our vision. What happens when the building constraints are severe and envelope and orientation aren’t negotiable? Good daylighting relies on a mix of ingenuity, muscle, and technology, whether it’s for urban infill or a fast-growing college campus, or for a suburb’s first stab at high-density development. More critical, say experts, is the ability to reconnect with history: relearning what a century with electricity has let us forget. With that in mind, consider the following lessons.

Photo Courtesy Pg&E, Pacific Energy Center
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1. Beg, borrow and steal.

No matter what the limitations, every building site has daylight assets, says Victor Olgyay, principal of the Rocky Mountain Institute and co-author of architectural lighting. “A real analysis of the resources available tells you where the opportunities and issues lie,” he says. “Then you can match those up with the building program, relating resource and need.”

Adds Tom McDougall, vice president of the Weidt Group in Minnetonka, Minn., and author of daylighting design, smart & simple, “spaces that need daylight must have access to the sky vault. If the angle from the window to the tops of adjacent buildings is 30 degrees, for example, you’ll need 70 percent window-to-wall area.” For skylights and toplighting, says Olgyay, “apertures can be oriented depending on your light source and tuned for the space’s needs.”

Creative building designs tap into neighbors’ exterior reflecting surfaces—a significant source of borrowed light. The north-facing courtyard side of a new gym for St. Francis College in Brooklyn has translucent panels because its neighbor is clad in Mylar-filmed glass, which throws ample sky brightness at the gym all year, says Murray L. Levi, project architect for Helpern Architects in New York City. Used carefully, even sidewalk light can help. “Ground-reflected light can be a huge extension of the building itself,” says Olgyay. “But it can compromise privacy, and sources below eye level can cause glare.”

Project teams can use tools such as the heliodon or simulation programs such as Radiance to evaluate exactly how much useful daylight a site has, although the latter requires user training and careful manipulation to ensure reliability. “With physical modeling, you don’t get the light leaks that digital models may have if polygons aren’t completely closed,” says McDougall. “But with building information modeling in the future, the digital side will just become more common.”

2. Study history.

Daylighting tools may be advancing, yet many of the materials and design strategies were invented long before cheap, plentiful electricity robbed our collective solar memory. “We’re repeating a lot of the history now, rediscovering old products that addressed light, heat, and view,” says Matthew Tanteri, a New York–based lighting designer. Translucent and optical materials, such as glass block and sawtooth and prismatic glazings, are making a comeback, as are refractive and flashed opal glazings and glass panels with white louvered shelves.

Century-old daylighting tricks still go a long way. At St. Francis College, the low roof of an existing structure deemed an “obstruction” by codes was covered with glass block, and the double-height basement below was captured as a light-filled library. “This was very common in the 19th century, often using ‘patent glass,’ ” says Levi. Applications ran from glass pavers over city sidewalk vaults to Turkish baths toplit by iron plates dotted with round glass lenses. In those days, design guidelines also mandated air shafts to boost ventilation, which were often painted a light color to improve daylight penetration.

To bring light deep indoors, historic structures commonly featured such light wells, as well as “finger plans,” atriums, and courtyards. Seminal examples range from cruciform 19th-century hospitals to doughnut office blocks such as Burnham and Root’s 1888 Rookery Building in Chicago. “Take a look at any old hotel in New York, Chicago, or San Francisco,” says Abby Vogen, senior project manager with the Energy Center of Wisconsin. “The fingers maximize the perimeter, bringing in as much natural light and ventilation as possible.”

The challenge today is balancing the natural amenity against reduced square footage. In fact, developers have found that sun-brightened spaces and operable windows command higher rents—a business case for more perimeter wall surface. “We used to do it, so we know it’s not impossible,” Vogen says.

3. Go long on tech.

Though historic landmarks sport proven technologies for bending and focusing light, recent years have added new fiber optics, plastics, special coatings, and even “active” glazings such as electrochromic panels that can be adjusted for variable illuminance levels. Other glass products incorporate louvers or triangular prisms that throw light deep inside floors or up at ceilings, with some customized for latitude and climate.

Proponents of new-wave materials include artist James Carpenter, whose architectural works deftly manipulate sunlight by means of novel lenses, mirrors, and specialty glazings. His 2002 Solar Light Pipe employs a roof-mounted heliostat and a prismatic glass cone to draw sunlight 140 feet down an 8-foot-wide sliver atrium in a Washington, D.C., law office. (At night, a xenon searchlight replaces the sun.) More recently, he and partner Davidson Norris used heliostats to brighten an outdoor space: Teardrop Park in Lower Manhattan.

“There’s no question these tools serve a very positive purpose,” Carpenter says. “Not just for visual impact but to adjust light levels or drive light into spaces where none existed previously. There are definitely calculable advantages,” such as improved productivity and occupant satisfaction.

4. Let the sun yield form.

The trendy glass box, while sexy and oh-so-minimal, is largely unsustainable. True daylight-driven designs respond to the variability of sunlight. “On most projects, the north and south facades are exactly the same, and that borders on criminal,” says Levi. Vogen agrees: “Each facade should have different window-to-wall ratios, and unique visible light transmittances.”

Contemporary clichés of daylighting design, such as the ubiquitous light shelf, should be employed thoughtfully, not as advertisements of green ideals. “I’m not convinced about the light-reflecting aspect of most light shelves,” says Mark McVay, design principal with SmithGroup in Los Angeles. “Yet they can be highly effective for shading.”

In this arena, McVay and others take inspiration from older and vernacular building types, such as the sawtooth roof forms of early 20th-century factories. “It was also common practice then to have higher floor-to-floor heights on lower floors to increase daylight penetration,” Levi notes. “On Georgian townhouses, with their graduated floor sizes, it’s very graphically clear.” Older structures offer other benchmarks. McDougall studied libraries built by Andrew Carnegie in the late 1800s and found room proportions that optimize solar illumination. “The typical reading room depth was no more than two times the window head height,” he says, conditions perfect for sidelit spaces. Another revelation: Wherever possible, bring in light from two sides.

“At the turn of the 20th century, daylighting was a real amenity and a real form-giver for architecture,” says Tanteri. “While we lost it with the International Style, there’s hope we’re returning to it today.”

C. C. Sullivan is an author and communications consultant specializing in architecture and technology.

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This article appeared in the April 2007 print issue of GreenSource Magazine

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