Reuse of cargo containers as building blocks in a small Seattle hybrid commercial building helps contain costs and speed construction.
As a result of the big American trade deficit, millions of surplus cargo containers have collected in or near large U.S. seaports. With a dearth of goods with which to fill return shipments to Asia, it has been more economic to build new containers in Asia than to bear additional costs to return empty ones. These stable, watertight structures can support more than 60,000 pounds (27,000 kg); have sturdy wooden floors and durable walls; can easily be transported by sea, rail, or truck; are interchangeable in dimensions with other containers; and can be interconnected with containers through simple, standard locking devices.
Less than a mile (1.6 km) from the Port of Seattle—through which millions of containers pass each year—a dozen surplus cargo containers have been used as building blocks from which to suspend floor, roof, and glass panels to form a new showroom and office for an interiors firm across from the Seattle Design Center in the increasingly trendy south Seattle Georgetown industrial area.
Because of the surplus supply, a 40-foot- (12-m-) long, eight-foot- (2.4m-) high, 320-square-foot (30-sq-m) used container can be obtained for less than $4 per square foot ($43 per sq m). Taller 9.5-foot-(2.9-m-) high containers were purchased for $3,000 each from a Seattle fabricator for the city’s first commercial cargo container project, says Jay Stark, developer and owner of Seattle-based DA Stark Interiors.
These containers have significant liabilities for conversion to buildings, the principal one being that they are narrow. Most rooms need to be at least 12 feet wide (3.7 m) wide to avoid making occupants feel claustrophobic. Cutting and fitting containers to open them up for light, air, and width adds significant cost and complication. Yet if the container structures are combined with floor, roof, and glass wall panel systems, efficient hybrid buildings can be created that are spacious and filled with light and air. “Our thesis is that containers do some things quite well, like providing shear strength and structural support, and structural insulated panels [SIPs] do what panels do best, which is to span,” explains architect Joel Egan of Seattle-based HyBrid Architecture, the firm that conceived the buildings.
The art is using containers to provide structure to support the spanning panels and to function as service spaces for such purposes as office modules, libraries, office equipment rooms, file rooms, bathrooms, kitchenettes, utility cores, mechanical rooms, and storage. Rather than cut into the containers to make them what they are not, panel systems can be used to expand the building to its maximum open potential. In the Seattle project, architects suspended the center floor bar joists between the containers by bolting the ends of the bar joists to ledgers that were installed by the container fabricator so that the container carries the weight of the center span as well as itself.
The hybrid of the container/panel system is what led to the maximum cost savings for the 7,200-squarefoot (670-sq-m) project. In one afternoon, a crane placed the 12 containers supporting the Seattle hybrid structure on a 7,000-squarefoot (650-sq-m) lot, and the building was completed five months later. The 16-foot-(4.9 m-) long SIPs were placed in less than two days. The short time frame sharply lowered the interest costs for servicing the construction loan obtained from a local bank, First Savings Bank NW of Renton. Despite the use of containers, the bank wrote a 25-year mortgage for the project.
Even larger cost savings resulted from the judicious sizing of the building to fall below the 5,000-square-foot (465-sq-m) threshold of the International Building Code (IBC) that would trigger many expensive upgrades.
The project was divided into two three-story buildings, each having a footprint of 1,440 square feet (135 sq m). Between the containers on the top level, a 20-by-40-foot (6-by12-m) floor span is suspended, supported by steel bar joists. On the bottom level, a mono-pour concrete slab on grade with a grade beam supports the containers and levels the floor between them. Bolted connections of the containers to a thickened reinforced slab, coupled with spot welding at container connections, were adequate to provide seismic stability even in the liquefaction zone on which the project sits. In the middle level, a fourby-20-foot (1.2-by-6-m) mezzanine bridge connects the two containers and reinforces the double height of the main retail floor.
The bottom level is retail space, the top level is office space, and the middle level is a half-floor mezzanine that allowed the building to be classified as a two-level building, thereby avoiding the necessity of installing a sprinkler system in the building. In addition, HyBrid Architecture designed the building with a single staircase and no elevator because the code allows for one staircase for commercial buildings at this scale, with a wider handrailto-handrail clearance than normal, provided occupant loads are less than 30 people and the distance is no greater than 75 feet (23 m) to the exit. Seattle permitted the buildings as Type V construction.
The various efficiencies of the design and construction reduced the construction cost by up to 40 percent of an equivalent commercial steel building built with conventional techniques, Egan says. “We’re able to build what’s basically a steel-framed building for the price of a wood-framed building,” observes building owner Jay Stark. He intends to use one of the buildings for the DA Stark Interiors showroom and offices, and lease out the other, which is its mirror image, to a design firm for rents in the low $20-persquare-foot ($215-per-sq-m) range.
The forms and aesthetics of the containers are preserved and exposed. The entire mass of the containers is visible both from the exterior and interior. While the end walls in the containers are furred out, insulated, and covered with sheetrock, the interior walls are left exposed on both sides. Seven feet (2.1 m) of the floor in the midlevel containers was removed to create a double-high space for the retail showroom below.
Reusing containers is far more environmentally friendly than using recycled steel because all the embodied energy both to make the original steel and fabricate the containers is retained and reused. For the balance, the project uses about 80 percent recycled material, by weight. The building is insulated with R-46 rigid foam construction panels that are 20 percent over code requirements and has high-efficiency windows, low volatile-organic-compound (VOC) paints, and carpets containing a high level of recycled content.
The wood floors of the containers are made of deep walnut-colored 17-ply, 1.25-inch- (3.2-cm-) thick Brazilian hardwood that has been refinished and reused. The building captures water that falls on the site with a planted green roof and a rain garden at ground level. Permeable pavers and grasscrete vegetated drive aisles feed rainwater into the ground. HyBrid Architecture processed the project through Green Factor, the Seattle Department of Planning and Development’s local version of the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system. The project achieved a Green Factor rating of 9.7 on a scale of 10; the baseline for a Green Factor designation is 3.
The two three-story buildings are Seattle’s first commercial buildings made from recycled cargo containers, according to both Stark and HyBrid Architecture. Egan notes that the container and panel system could be disassembled relatively easily and the buildings moved. The virtue of that, he says, is that a developer could build a container/panel building at a lower density than the site could ultimately support economically—of particular value in the current economic climate. When the market allows greater density at the site, rather than lose its capital investment, the developer could relocate the building to another site and construct a building at greater density at the original site. In the meantime, the container/panel building income could offset the carrying costs of the land, thereby preserving its appreciated value potential when the market matures.
“Relocatable, subcode-threshold, placeholder container/panel buildings are the 21st-century future for underused lots,” predicts Egan. The developer earns money, the neighborhood gains value, and the city gains density and tax revenues, he points out.