Metal With Pizzazz
"Audacious curves." "Cool coatings." "Vibrant colors."
These are not phrases typically attributed to metal roofs. But they represent a new look to an industry that is still perceived by many in design and construction to be as Plain Jane as it gets.
"To this day, there are people who think metal roofing can be nothing but unpainted metal," says Scott Kriner, technical director of the Metal Construction Association, Macungie, Pa. While the bare metal roof of yesteryear continues to play a key role in the construction industry — from high-end architecture to warehouse and industrial buildings — new products and processes have expanded the applications for metal roofing, especially in the steep-slope market.
"Metal can duplicate almost any other roofing product available," even asphalt and wood shingles, says Kriner. Most metal roofing vendors can meet virtually any custom color request, and you don't have to worry about fading. "You can get products today that have a 30-year warranty against any noticeable fade in color," he says.
The latest step in metal roofing, says Kriner, is the integration of infrared reflective pigments that give dark-colored metal roofs higher levels of solar reflectance and infrared emittance, resulting in lower roof surface temperatures. IR pigment and coating vendors, such as Valspar Corp., Minneapolis, are partnering with metal roofing manufacturers to offer "cool" color products. Almost all metal roofing manufacturers are coming out with cool color palettes, says Kriner.
That means architects can specify darker colors, like earth tones, and still meet the solar reflectance and infrared emittance requirements set by EPA's Energy Star and similar standards. For instance, forest green, brown, and blue meet Energy Star's solar reflectance requirement of 0.25 for steep-slope roofs, while providing infrared emittance of 0.90. Lighter colors, such as almond, sandstone, and white, can achieve solar reflectance of 0.50-0.73, meeting Energy Star's standard for low-slope roofs.
Kriner says the green building movement and increased concern for urban heat island effect have spurred a sizable market for cool roofing, especially in the South. But even northern cities like Chicago have adopted cool roof requirements to reduce heat island effect. (See BD&C, February 2003, page 64.)
The Cool Metal Roofing Coalition, a trade association formed in 2002, is working with the U.S. Green Building Council to advance metal roofing's standing in next version (LEED 2.2) of the council's Leadership in Energy and Environmental Design green rating system. The current version of LEED limits the credit that a metal roof can achieve.
Undulating and curved metal roofs, such as the one that tops the five-story Barton Skyway IV office complex in Austin, Texas, are among the top aesthetic trends of metal roof designs.
CMRC is also working with the state of California on the next version of its newly adopted Title 24 energy code. Under the current version of Title 24, unpainted metal roofing does not meet the prescriptive requirements for cool roofs, according to Kriner. Bare metal roofs inherently have high solar reflectance — between 0.60-0.70, according to a research by Oak Ridge (Tenn.) National Laboratory — but very low infrared emittance (under 0.10).
While coated steel holds the lion's share of installed metal roofing, titanium, zinc, stainless steel, and aluminum are gaining acceptance among architects in the U.S.
Zinc, for instance, has what Kriner calls "tremendous corrosion-resistance." It corrodes by forming an oxide on the surface that "tends to wash away," and it has a dull, gray appearance that designers like San Francisco-based architect and University of California, Berkeley, professor Stanley Saitowitz find desirable. "It's metallic, but not shiny," says Saitowitz, who specified zinc roof and wall panels for a three-story apartment complex in San Francisco. The material was formed into standing seam panels that transition from the vertical wall to an elliptical roof.
Stainless steel and titanium, made popular by the undulating designs of Frank Gehry, have similar corrosion-resistance properties. The metals can also be colorized through metallurgical processes that involved creating a titanium oxide or chromium oxide layer that "interferes" with light, says William Zahner, president of architectural metal designer A. Zahner Co., Kansas City, Mo. The company developed the stainless steel façade for several Gehry projects, including the Experience Music Project in Seattle.
Improvements in coatings and pigments for metal roofs allow manufacturers to offer long-term warranties against fading.
"By changing the thickness of the film, you can change the way light reflects off that surface in the base of the metal, kind of like an oil slick," says Zahner. There are no dies or pigments within the metal itself, so it is virtually impossible for the metal to fade.
Through other metal-working processes, the Zahner firm can alter the patina of metals like copper and zinc to produce unusual colors — orange instead of green in copper, for instance.
Looking ahead, Zahner says his company is planning to develop a method for adding form and texture to metal façades and roofs, using laser technology. He points to a San Francisco museum the firm is currently working on where an image of light coming through trees is being "formed" onto the 400-foot-long copper exterior by "pushing and pulling" aspects of the metal.
"We're not using lasers yet, but we are converting the image through a computer algorithm to machines that form the surface of the copper façade, canopy overhang, and tower," says Zahner.