The New Age Steel

"The New Age Steel" published in Design Today, August 2011



Cor-Ten steel, also known as weathering steel given its distinctive rust covering when exposed to the elements, is more popular today than ever in architecture. This comes even as the United States Steel Corporation, the trademark owner of Cor-Ten, asserts that the steel should not be used in architectural applications, such as roofing and siding. Yet large buildings of all sorts around the globe can be found covered in the rusty steel. Some recent ones of note include the Echigo-Matsunoyama Natural Science Museum in Japan (2003), designed by Tezuka Architects with load-bearing walls and a roof of Cor-Ten steel; the Santa Mónica Church (2008) in Madrid, Spain by Vicens + Ramos, which features a stunning periscoping façade; and Feilden Clegg Bradley’s Broadcasting Place (2009) in Leeds, UK, a 23-story mixed-use tower that was the recipient of the Council on Tall Buildings and Urban Habitat’s 2010 Best Tall Building award, winning over much taller and more well-known Burj Khalifa in Dubai.

In residential architecture, as will be seen, the use of Cor-Ten is no less interesting, but it’s worth taking a look at a brief history of the material’s use in art and architecture to understand its effects and appeal. In the 1960s the material was popular as a cladding for Modernist office buildings in the United States, most notably the John Deere World Headquarters in Moline, Illinois by Eero Saarinen (1964), the Ford Foundation Building in New York City by Kevin Roche John Dinkeloo (1968), and the U.S. Steel Tower in Pittsburgh, Pennsylvania by Harrison, Abramovitz & Abbe (1970), built as a showcase for the client’s own Cor-Ten product, still fairly new at the time.

Contemporaneous with these buildings were large-scale public sculptures, many occupying plazas in front of Modernist glass-and-steel high-rises. Pablo Picasso’s 1967 cubist creature, known as The Picasso, in Chicago’s Daley Plaza is an early example. Yet it is the abstract sculptures of Richard Serra in the ensuing decades that are immediately associated with the material. His Cor-Ten steel constructions litter public spaces and museums from Bilbao to New Zealand.

In both realms of art and architecture, Cor-Ten steel produces a monumentality that, in the case of architecture, gives weight to the otherwise light and transparent Modernism, and in art it gives abstract art a texture and color that situates it in opposition to the surroundings, be it natural or manmade. Monumentality and contrast are but two apparent traits of Cor-Ten steel, regardless of form or composition.

So what exactly is Cor-Ten steel? In Victoria Ballard Bell’s indispensable book Materials for Design (Princeton Architectural Press, 2006), it is defined as “an alloy metal in which a small amount of copper and other elements are added to steel…[so] the exposed surface quickly oxidizes in the atmosphere, forming a dense, shallow, passive barrier against further corrosion.” Therefore Cor-Ten steel is used almost exclusively for exterior applications, though it can be brought inside if the oxidation occurs before installation.

On facades, the typical application of the material, the rust barrier that forms does have the disadvantage of staining adjacent materials through precipitation. Concrete sidewalks, for example, will turn reddish-brown, unless an integral channel and drain funnels the stained water, as some buildings from the 1960s took into consideration. Another way to deal with the inevitable is to choose a surface material—brick is a good one—that will not exhibit the staining like gray concrete. Some architects also promote using a clear varnish after the rust has formed on the steel, so rain will shed off the facade without staining.

While Cor-Ten steel is by definition a weatherproof barrier that is basically maintenance-free, another disadvantage is cleaning the surface to remove graffiti. A townhouse completed in 2002 in San Francisco's hip yet gritty South of Market area was overhauled by architect Jim Jennings when his original front of Cor-Ten steel was repeatedly tagged. Removing the paint meant removing the rust, which resulted in a splotchy appearance that could not be remedied by painting the bare steel beneath; a stainless steel facade following the original perforated design has since been installed.

Such will not happen at 700 Palms Boulevard in Venice, California, a corner where a 2003 house prominently clad in Cor-Ten steel sits behind a perimeter wall, keeping taggers at bay. Designed by Steven Ehrlich with “raw, honest materials appropriate to the grittiness of Venice,” this steel façade overlooks the intersection as well as the owner’s lap pool. A rectractable awning with orange fabric complements the rust-colored wall while shading the pool. This awning also shades the Cor-Ten steel wall itself, important since the material has low solar reflectivity, meaning it stores heat during the day and releases it at night. This ventilation works well in climates with large day-to-night temperature swings, but it also contributes to the urban heat island effect. In general this points to considering the orientation of any facades with the material and the extent of its use. Minimizing the material may actually be aligned with the perception of the weathering steel as something special that stands in contrast to other materials, be it brick, wood, glass, concrete, or another metal. At 700 Palms, the Cor-Ten steel cladding sits beside concrete blocks and wood siding in a carefully considered composition.



A much smaller use of Cor-Ten steel can be found on the front of a townhouse in New York City’s Meatpacking District, about a block from the popular High Line elevated park. Matthew Baird’s 2005 design (photos above) recalls the sculptures of Richard Serra, because a single piece of 1-1/4” (32mm) thick weathering steel, 14 feet wide by 34 feet high (4.25m x 10m), hangs in front of three floors of the glass façade. The piece is so big, that in order to truck it into Manhattan from New Jersey a portion of one of the George Washington Bridge had to be closed! Raised above the ground floor’s entrance and garage door, the slab of Cor-Ten steel is an imposing presence on a narrow building between its historical neighbor to the south and a much larger building to the north. The townhouse stands in contrast to both of its neighbors, while it also recalls the industrial past of the area, if in an abstract and artistic manner.

In the American Midwest, about halfway between Baird’s and Jennings’s East and West Coast townhouses, there is a house with a skin of Cor-Ten steel, designed and built in 2001 by architecture students at the University of Kansas. Studio 804, headed by architect and professor Dan Rockhill, focuses on affordable housing in marginalized communities. The Random Road project shows that Cor-Ten steel can be utilized even with a low budget; it is not only for clients who can pay to close major urban thoroughfares. Affordability comes from using 0.1-inch (2.5mm) thick steel plates applied like a rain screen and overlapped like shingles, instead of going for Serra-esque effect with thick plates. Since the Cor-Ten is installed as a rain screen, furred from the weathertight wall behind it, the shingles project in front of the concrete footing and therefore don’t stain the concrete.

One last example of recent residential architecture incorporating Cor-Ten steel illustrates that even the effects of monumentality and contrast can be overcome when treated carefully. The 2005 Planar House, designed by Steven Holl for a desert site in Arizona, uses the material sparingly, next to tilt-up concrete panels that comprise the majority of the house's exterior. Cor-Ten is used for the garage door, but it is perforated to admit light in both directions—the lantern-like effect after sundown is stunning—and make the material lighter in appearance. Carried into the courtyard, the perforated steel panels angle to follow a ramp, and a steel door cut from the wall provides access to the courtyard's pool. The monumentality associated with the weathering steel disappears in its treatment as a canvas for abstract cuts and in its relationship to the more solid and thicker concrete walls. In concert with the tilt-up concrete—often associated with warehouses and other industrial applications—the Cor-Ten steel is colorful but complementary, as if they belong together.

Cor-Ten steel is quite an interesting material in the realm of contemporary architecture: It presents a striking monolithic appearance with subtle differences in browns and oranges; it offers a low-maintenance cladding for buildings; and in the way that it rusts Cor-Ten steel is like a living façade, changing quickly and then slowly over time. This small sampling of rusty residential architecture hopefully illustrates the appeal of this material and the various ways it can be implemented. These houses make it clear that architects can use Cor-Ten steel above the objections of its trademark holder U.S. Steel. Nevertheless architects willing to incorporate the material in a project should take care with the detailing, installation, and if possible the maintenance, so the inherent corrosion of the steel does thin it out to the point of perforation or breaking. When considered carefully the effects are sublime, creating standout buildings in any context.