In 1964 Deere & Company opened a new headquarters in Moline, Illinois, designed by Eero Saarinen, and its engineers were nervous. The building was clad in Cor-Ten, a steel that U.S. Steel had developed in 1933 for railroad hopper cars, meant to rust on purpose. A farm equipment company that had spent decades warning farmers about rust was about to wear it on the outside!
It was one of the first architectural uses of weathering steel in the country, and it changed what a facade could be. Not a finish applied once and maintained forever. A surface that would keep changing, on schedule.
A wall is a set of clothes
The idea that a building’s skin can be its own thing, separate from its structure, goes back at least to Gottfried Semper, the German architect who published The Four Elements of Architecture in 1851. Semper argued that woven textiles were one of architecture’s primal sources and that a building’s cladding, its dressing, carried more meaning than the frame behind it. He called it the principle of cladding.
Modern construction made him right in a way he couldn’t have pictured. Most contemporary walls are layers: structure, insulation, a weather barrier, a ventilated gap, then a rainscreen of whatever the architect chooses. Because the outer layer isn’t holding anything up, it can be swapped, mixed, patched together from different materials on different faces of the same house.
Which is the opportunity, and also the trap.
Three materials, three clocks
The reason wood, metal and stone show up together so often is that each one ages at a different speed, and good architects use that.
Unfinished wood turns silver. Ultraviolet light breaks down lignin at the surface, rain rinses it away, and within six to twelve months dark fungi move into the cellulose that’s left. Then it erodes, slowly. Research summarized by Philip Evans at the University of British Columbia puts the loss at about 12 millimeters per century for western red cedar facing south, roughly 6 for denser Douglas fir. The Japanese technique of yakisugi, charring cedar boards before they go up, dates to the Edo period and gives wood a carbon skin that sheds water and deters insects. Terunobu Fujimori’s Yakisugi House in Nagano, finished in 2007, has charred boards that warped in the fire and gaps filled with white plaster. It’s striped like a zebra! We love it.
Weathering steel stabilizes. Its rust layer forms through cycles of wetting and drying, then slows to almost nothing. The catch is everything below it. The early, loose rust runs off in the rain and stains pavement and stone in umber streaks, which is why careful detailing keeps the water off the concrete. And in salty sea air the patina may never settle down.
Stone barely moves at all. When Peter Zumthor built the thermal baths at Vals in Switzerland, opened in 1996, he stacked layer on layer of Valser quartzite quarried nearby and set the building into the hillside under a grass roof. The stone isn’t cladding there so much as the whole idea.
When mixing goes right, and wrong
The project we’d send anyone to first is Dominus Winery in Napa Valley, Herzog & de Meuron’s first American building, completed in 1997. Its walls are gabions, wire cages packed with locally sourced basalt. Light comes through the gaps, so the interior is lit by a wall that looks solid from the road. The stone moderates the temperature inside, warming slowly and cooling slowly. From a distance it could be a retaining wall in a vineyard, and that modesty is part of the design. It’s one material, used in two densities, and it reads as both rough and precise. That’s the lesson. Mixing works best when the materials are doing different jobs.
The version that doesn’t work is everywhere in new suburbs. A strip of fake stone at the base of the front wall only, wrapped around the corner by about eighteen inches, then vinyl. A band of horizontal metal on one bay because a rendering needed contrast. Materials stop at the corner like stage flats, and the house gives itself away the moment you see it from the side. A facade is three-dimensional. It gets read from the sidewalk, the driveway and the neighbor’s yard. Stone has weight, so it should sit low and carry the eye down to the ground. Wood should go where people touch it and see it age. Metal is best at edges, roofs and the places where water needs to leave quickly.
The material that wins, in the long run, is the one whose aging you planned for. Saarinen’s Deere headquarters is still there, the color of the woods around it, and still unpainted.
For more skins worth a close look, see a Cor-Ten house in a Ukrainian forest, a woven steel facade in St. Petersburg that Semper would have enjoyed, and the timber tower now rising over Sydney.
