Let It Rain, Let It Rain, Let It Rain by Aaron Seward
Credit: Barbara Karant/Kohn Pedersen Fox Associates
Rainscreen section, Ross School of Business, Kohn Pedersen Fox Associates
Payette used a terra-cotta rainscreen system to cover the entrance face of the Meditech Computer Science Building. In addition to offering a contemporary riff on the areas historical architecture (mills built from stone), the terra-cotta absorbs the sun’s heat, insulatating the interior with an R-value of 12.5.
Rainscreen section, Meditech Building, Payette
Credit: Robert Benson Photography
Terra-cotta rainscreen systems have been in German façade manufacturers’ catalogs since at least the 1980s. But this marriage of an ancient material with a more contemporary construction methodology has only really caught on in the United States over the past decade. In that relatively brief amount of time, however, this nation’s architects have put the system to good use both in solving project-specific design challenges as well as in foiling one of the chief enemies to a building’s longevity: water infiltration.
The traditional way to keep water out of a building has been to seal the envelope, generally with caulking. This has one major fault. Caulking materials inevitably deteriorate. Weather causes them to expand and contract, and eventually crack, while UV rays corrode them. Meanwhile, wind, or the inevitable pressure differential between interior and exterior, causes water to worm its way into the exterior.
Rainscreens, of whatever material, answer this problem by doing away with caulked façade joints and replacing them with a vented cavity between the cladding and insulation, where the final weather barrier is established. This eliminates the pressure differential and allows the water that does invade the system to be harmlessly vaporized.
A multitude of materials can be employed in rainscreen systems, including woods, metals, and masonry. Terra-cotta, however, offers a relatively affordable way to achieve a durable finish, with a wide spectrum of design possibilities. The material can be manufactured in almost any color imaginable, and in extrusions limited only by physics and the architect’s imagination. The three projects that follow are examples of designers using terra-cotta rainscreen systems to develop a contemporary response to built environments dominated by brick and stone.
Ross School of Business, University of Michigan
Kohn Pedersen Fox Associates, 2008
When the University of Michigan hired Kohn Pedersen Fox Associates (KPF) to design a new 281,000-square-foot home for its school of business in Ann Arbor, Mich., the architects found themselves facing the challenge of integrating their building into a context of revival styles. The project sits diagonally across from the neo-gothic William W. Cook Law Quadrangle. “The client had an inclination to use a material that would enable the building to be perceived as a good neighbor to the campus’ traditional buildings, and a material that would last with a high level of elegance over the life span of building, but we didn’t want to do brick or gothic, exactly,” explains William Pedersen, FAIA, the design principal for the project. “A terra-cotta rainscreen seemed perfect. The modular nature of its construction lends it a certain modernity, and it blends well with a masonry context. It also goes well with glass and stone.”
The architects used the terra-cotta in two different applications: as larger surfaces with no fenestration, and as vertical punctuation elements on the glass-and-aluminum curtainwalls. Only the unpunctuated surfaces employ a true rainscreen system. The tiles hang from aluminum clips attached to metal stud-framed walls. From interior to exterior, the wall sandwich is assembled like this: metal studs, gypsum sheathing, bituminous sheet waterproofing, 3-5/8 inches of mineral-fiber insulation, an air barrier, a 1-3/4-inch vented air space, and, finally, the terra-cotta cladding. “We wrapped the mineral-fiber insulation with an air barrier in case any wind-driven rain got behind the terra-cotta,” says KPF senior associate principal Phillip White, AIA. “In Europe, they typically don’t add that, but we did because when insulation gets wet, it loses its value.” The architects subjected the system to a battery of performance testing and believe the wall to provide an R-value of 16.
While the terra-cotta’s red-brown color is vibrant on its own, the architects took full advantage of the sculptural properties of the material to add texture to the surfaces of the building by using vertically fluted tiles. In half of the fluted pieces, the flutes point slightly to the right, whereas in the other half, they point the same degree to the left. These ridged tiles are alternated on the wall with the flat tiles, giving the otherwise planar surface an interesting texture. The tiles—which vary in size but are, for the most part, roughly 1 foot by 2 feet 5 inches—were also hung oriented vertically (most terra-cotta rainscreen systems feature horizontally hung tiles). This allowed the crisp joints between tiles to further strengthen the lines of the building.
The sculptural tiles did add cost to the system, but KPF worked with the manufacturer to reduce the number of extrusions to 10, thus keeping the price tag within reason. The wall was stick-built on site and cost approximately $70 per square foot—far cheaper than the project’s curtainwall, which rang in at around $120 per square foot.
Meditech Computer Science Building
Medical Information Technology, or Meditech, is a healthcare software developer, one of the industry’s leaders in hospital records database management. When commissioning a computer science building for its new 17-acre campus on the northern shore of South Watuppa Pond in Fall River, Mass., the company wanted to embody its high-tech culture and yet nod to the area’s historical architecture. In the 19th century, Fall River was a center of American textile manufacturing, and many of the old mills—constructed from local stone—still dot the landscape. Boston architecture firm Payette looked to these structures for inspiration when designing the 120,000-square-foot building, a strategy that led the architects to clad half of the facility in a terra-cotta rainscreen system. “Although terra-cotta is a very ancient material, its application in a rainscreen offered a way to reinterpret the mills in a contemporary way,” says Payette associate principal Jeff DeGregorio, AIA.
The terra-cotta rainscreen clads the entrance face of the building and is outfitted with punched windows set in a pattern much like that found in the local textile mills. This relatively closed façade stands in contrast to the opposite face: a floor-to-ceiling glass curtainwall that allows Meditech employees to take in views of the water and the landscaping. In addition to establishing an open and closed dynamic, the opposing façades are oriented optimally for sun exposure, with the terra-cotta and its superior insulation values accepting the lion’s share of the summer sun and heat. The punched windows are triple glazed for the same reason. The terra-cotta features an R-value of 12.5, whereas the windows have R-values from 4.5 to 5.6 in the summer and 4.2 to 5.5 in the winter.
To add variety and texture to the terra-cotta façade, the architects designed a stripe pattern in the chalky white tiles, which are 3 feet 4 inches wide by 14 inches high. The pattern was accomplished by extruding each tile with a 2-inch-wide horizontal stripe of honed finish at the bottom and the remainder of the tile with a corduroy pattern. “We went through a long process with the manufacturer and looked at 70 to 100 different samples of terra-cotta to get to the right coloring and texturing,” DeGregorio says. “There was no amount of rendering or computer modeling that could tell us if the building was too stripy or not stripy enough. Terra-cotta offered us the flexibility to actually mock-up lots of different pieces and see what worked.”
Rather than stick-build the rainscreen system, Payette had it prefabricated in 30-foot-wide by 14-foot-high panels that were trucked to the site, then hoisted into place by crane and clipped to the floor slabs. This saved time and money on installation and made the process easier in the face of the site’s strong winds. Each panel, from interior to exterior, was made up of 6-inch cold-formed metal framing, 5/8-inch exterior sheathing, an air and vapor barrier, 2-inch rigid insulation, a 1-3/4-inch vented air gap, a vertical aluminum rail that accepts the terra-cotta, and then the tiles themselves, which were shiplapped. The windows were installed later. “We worked hard on the details to make sure the air and vapor barriers were secured and used the cladding to keep as much of the system as watertight as possible,” DeGregorio says. The system was bid at $80 per square foot, not including the windows.
Crimson Hall, Bridgewater State University
DiMella Shaffer, 2007
In designing Crimson Hall, a 130,000-square-foot student residence at Bridgewater State University, Boston architecture firm DiMella Shaffer combined terra-cotta rainscreen, brick cladding, and glass curtainwall to create the building’s envelope. The decision was, in part, one of contextual sensitivity. “The rest of the campus is made up of multimaterial structures that mix brick and precast concrete and things like that,” says firm principal Ed Hodges, AIA. “I wanted to keep our building in that tradition.” The proportion of material to material, however, came down to a matter of cost. Availed of a tight budget and an expedited construction schedule, the architects clad most of the building in brick, saving the curtainwall and terra-cotta for the standout elements of the facility.
DiMella Shaffer used the rainscreen system on about 25 percent of Crimson Hall. A desire to emphasize the mélange of materials guided the architects’ detailing of the terra-cotta. The sandy-colored tiles themselves are 14 inches high by 4 feet long, allowing the terra-cotta surface to pop next to the smaller red bricks.
Construction of the project began in March 2006, with a completion date set in July of the following year. This meant that the cladding would have to be erected during the winter months. In this case, the terra-cotta rainscreen system was a big help to DiMella Shaffer because it employs a dry installation process. The system was built layer by layer on top of metal studs. The wall composition, from interior to exterior, consists of gypsum wallboard, metal studs, sheathing, an air barrier, 2-inch mineral fiber insulation, a 1-3/4-inch air gap, and, finally, an aluminum rail system upon which the terra-cotta tiles were clipped. The windows in the wall were set back at the water barrier and flashed with aluminum and membrane flashing.
At around $50 square foot (in 2007 dollars), the terra-cotta rainscreen system at Crimson Hall was a bargain. Its R-value of 12.15 also helped the project to achieve LEED certification. But the real value may be in the system’s durability. “Because there’s no caulking in the rainscreen system, it doesn’t require a lot of maintenance,” Hodges says, “and that’s crucial for any material you use in a building that’s going to last 100 years.”