Some Assembly Required

Five firms explore the potential of prefabrication with digital tools, a diversity of materials, and varying degrees of on-site labor

Joann Gonchar, AIA

Like a strange, transplanted suburban subdivision, five single-family houses have sprouted on a 17,000-square-foot empty lot in Midtown Manhattan. The homes, which include a tiny cube intended for short stays, an elegant spruce box assembled like a piece of Ikea furniture, and a four-story structure wrapped in transparent plastic, are part of the exhibition Home Delivery: Fabricating the Modern Dwelling at the Museum of Modern Art (MoMA) through October 20.

Inside the museum, just next door to the lot, is a crash course in the history of prefabrication in domestic architecture. With drawings, models, film clips, full-scale reconstructions, and other artifacts, Home Delivery traces prefab's early roots with objects such as the portable cottage that London carpenter H. Manning designed for British colonists settling in Australia (1833) and Thomas Edison's Single Pour Concrete House system (1906). The exhibition follows developments in Europe and America in the 1920s and '30s, with work from architects including Buckminster Fuller, Walter Gropius, and Le Corbusier. It explores the post−World War II years, when burgeoning demand for housing prompted mass-produced solutions such as the Lustron Corporation's steel-framed and enamel-panel-clad houses, and continues into the 1960s and '70s with the work of the Metabolists, both fanciful and realized. The exhibition also shows how recent technical advances in digital design and fabrication are fueling experimentation with objects such as a wall fragment designed by New York City−based Jesse Reiser, AIA, and Nanako Umemoto, who have perforated a sheet of steel to create a diaphanous and undulating scrim.

 

Photo © MOMA/Richard Barnes

 

But it is outside, on the adjacent lot, where visitors get a real sense of the current potential of the prefabricated dwelling. The houses installed there demonstrate how prefab can be deployed not only to deliver shelter, but also to provide more environmentally responsible, higher-quality buildings, constructed faster, and in some cases, at lower cost. The outdoor exhibition also shows that prefab no longer means a one-size-fits-all, cookie-cutter approach, but instead makes possible adaptable, custom-tailored solutions.

For this part of the exhibition, the museum commissioned houses from five architects after inviting proposals from 21 firms. The completed buildings respond to very different programs, ranging from a vacation house to a one-room cottage for displaced residents of New Orleans. The goal was "to get five very diverse positions," says the show's curator, Barry Bergdoll, MoMA's chief curator of archtitecture and design. They also needed to be commercially viable. "Even if they were prototypes, they had to be absolutely feasible," he says.

The museum announced its selection in early January, leaving the firms about 6 months to finalize designs and coordinate fabrication and installation-a process that each team was required to document in an online journal (www.momahomedelivery.org). And though they each received a stipend of $175,000, the architects were responsible for raising the needed funds in excess of that amount.

 

The Cellophane House (at left above) is a transparent interpretation of a Philadelphia row house. Acrylic interior partitions, walls, and ceilings seem to glow with the help of integrated LED lighting. Photo © MOMA/Richard Barnes

 

 

All wrapped up

Of the five houses on the MoMA lot, the one that is the most outwardly futuristic is the four-story house designed by Stephen Kieran, FAIA, and James Timberlake, FAIA, of Philadelphia-based KieranTimberlake Associates (KTA). With its exposed structural frame, transparent envelope, and translucent floors and stairs, the Cellophane House may lack the privacy that most home buyers desire, but it "is intended to be more provocative than practical," explain the architects.

The Cellophane House has an energy-generating double-skin envelope. Photo © Peter Aaron/Esto

 

Cellophane's structure is composed of logical and transportable "chunks." Photo © Albert Vecerka/esto

The project continues the investigation into building-supply chains and prefabrication processes that the architects explored with their Loblolly House, a second home for Kieran's family on Taylor's Island, Maryland, completed in late 2006 [architectural record, November 2006, page 185]. As at Loblolly, Cellophane's structural frame consists of extruded aluminum, off-the-shelf components typically used for factory and temporary-structure applications. These members are attached with the manufacturer's standard fittings, along with custom steel connectors and braces designed to handle shear and wind loads. Since the frame relies on "dry joints," rather than welded connections, the house can be readily disassembled, and individual components can be reused or recycled.

To speed on-site work, KTA divided Cellophane into 14 logical and transportable modules, called "chunks." Each is composed of the aluminum structure with the floor and some perimeter walls attached. The chunks, assembled in Lebanon, New Jersey, by modular fabricator Kullman, were delivered to the site individually on flatbed trucks over three days in late June in the order of their assembly sequence. Other elements, such as most interior wall partitions, were installed after contractors hoisted the chunks into place.

Much of Cellophane is enveloped in a transparent material that KTA has been developing since 2002 and calls SmartWrap. The thin-film skin consists of an outer layer of the plastic polyethylene terephthalate (PET), and integrated photovoltaic (PV) cells. An inner skin includes a film that blocks ultraviolet light and helps mitigate heat gain. Between the two layers is a cavity designed to trap heat in the winter and vent it during the summer in order to reduce energy expended on heating and cooling.

Although Cellophane's structure and envelope are unusual, the project's larger innovations are process oriented. Because KTA designed the house in three dimensions with a building information model (BIM), the architects could assume many of the tasks typically performed by a construction manager, such as developing shop drawings, generating lists for ordering parts directly, and tracking data such as costs and weight.

A decorated shed

The one-room house designed by a team from the Massachusetts Institute of Technology (MIT) benefited from many of the same digital processes behind the Cellophane project, but with a completely different result. Instead of a Modernist dwelling of novel materials, Digitally Fabricated Housing for New Orleans is a pitched roof cottage made largely of plywood and adorned with a decorative frieze.

The 350-square-foot dwelling's form and its traditional ornament were controversial among faculty members at MIT, according to Larry Sass, an assistant professor in the school's department of architecture and the leader of the project team. "When I first showed my ornate models to a few colleagues, some were appalled that my work did not reflect the Modern movement in architecture," he says.

For Sass and his students, however, there was no requirement that a prefabricated house conform to a particular language. "This delivery system and digital process is not limited to one architectural style," says Daniel Smithwick, one of Sass's research assistants. "It can produce a Modernist cube just as easily as a Victorian mansion," he says. 

 

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A team from MIT developed a house for New Orleans (1) with a digital model (2 and 3) and a series of physical models and full-scale prototypes. The resulting structure is composed of bilateral ribs, largely of plywood, with some high-density polyethylene elements (4). The pieces were assembled on-site with rubber mallets (5 and 6) and are held together by friction, rather than nails, bolts, or other mechanical fasteners. Photo courtesy Larry Sass/MIT

 

 

The MIT prototype has a structure of bilateral ribs made of more than 4,500 pieces milled from plywood with a computer numerically controlled (CNC) cutting machine-one that relies on digital information to direct the selective removal of material. Over three weeks, the installation team of Smithwick and fellow research assistant Dennis Michaud put the house's notched pieces together on the MoMA lot with rubber mallets. Friction between the elements' tabs, slots, and grooves holds them together, rather than bolts, nails, or other mechanical fasteners. They also applied glue to key joints, though it is not critical to the building's structural integrity, according to Michaud. "It was a concession to the engineer," he says.

Sass and his students developed the "snap-and-fit" assemblies with a combination of parametric modeling and BIM. The resulting digital model described the geometry of the house's components, but also took into account criteria such as material behavior, manufacturing processes, and the sequence of assembly. Along the way, they tested and adjusted the digital model with a series of small-scale physical models and full-scale prototypes made through laser cutting, CNC-milling, and 3D printing. With the refined digital model, they then cut the building's actual components from 600 sheets of plywood at a lumber yard in Exmore, Virginia.

Once the components were delivered to MoMA in mid-June, assembly proceeded relatively smoothly. However, the interface between the prefabricated foundations and the traditionally constructed slab-on-grade presented a slight glitch. Although Sass and his team had accounted for irregularities in site conditions by designing base blocks that allowed adjustment, they did not know in which direction to move the blocks until several days into assembly, when some parts were not fitting correctly. At that point, they needed a forklift to nudge the already constructed portions of the house together. Almost all of the teams had similar difficulties, according to Jay Gorman, project manager for F.J. Sciame, MoMA's construction manager. "Meeting the ground is one of the challenges of prefab," he says.

A house unfolds

All of the houses on the MoMA lot have very rectilinear geometry, except for the project called BURST*008. Raised on steel pilotis, it has a C-shaped section, one completely glazed elevation, and a bleacherlike stair connecting the living area with the ground. Designed by New York City−based architects Jeremy Edmiston and Douglas Gauthier, BURST*008 is made of 725 nonidentical plywood ribs attached to each other with steel X-clips. The resulting cagelike lattice is clad in structural insulated panels (SIPs)-a sandwich of rigid insulation between two sheets of oriented strand board.

 

BURST*008 (1) is made of 725 nonidentical plywood ribs joined with steel clips to form a latticelike structure (2 and 3). The ribs and clips were assembled off-site and packed in three tightly stacked piles (4) for transport to MoMA. There, contractors unfolded the stacks like an accordion (5) and secured them to an already-installed steel piloti system. Installation of the exterior skin of SIPs (6) completes the BURST*008 structural system. The panels were CNC-milled and cut with grooves to accommodate the underlying ribs precisely. The ribs lock the skin in place and hold it taut. Photo and drawing: courtesy System Architects and Gauthier Architects (2,3,4,5)

 

 

In a process similar to that of the MIT house, the ribs were CNC-milled at Associated Fabrication, in Brooklyn, New York. With specialized nesting software, the company determined how to distribute the rib pieces on the fewest number of standard 4-by-8-foot plywood sheets. But for the MIT project, the layout of the individual elements on the plywood sheets was organized according to the order of assembly. "We had to balance assembly efficiency and waste," explains MIT's Michaud. 

The Burst team's choice to nest the irregular pieces meant labor-intensive sorting of all the components. "While this process was time consuming and required attentiveness and many hands, it did not require any specialized building expertise," point out Edmiston and Gauthier.

The two had built a version of the house three years before on the east coast of Australia as a vacation home for a young family. For that house, the architects sorted the pieces on the construction site. But at MoMA, they did not have the requisite layout space. So Gauthier and Edmiston rented a Brooklyn warehouse, where their assembly team organized the plywood ribs and attached the steel clips. Contractors transported these preassembled ribs in three tightly packed piles to Midtown on a flatbed truck, and then unfolded the stacks accordion style before securing the lattice to the house's waiting steel pilotis.

The final step of the assembly process was installation of the SIPs floor and cladding, which serves not only as the building skin, but also as an essential part of the structure. Like the ribs, the cladding was CNC-milled and also precut with grooves that accommodate the ribs precisely. The substructure locks the skin in place and holds it taut like a drum, explain the architects.

Of the five houses, Burst had the longest on-site installation process-about five weeks. Given the amount of hands-on assembly required, Gauthier and Edmiston concede that the term "prefab" may not be an entirely appropriate label. "It might be more accurate to call BURST*008 a kit home, but even that is not entirely accurate," they say. "It is all about controlling smaller pieces."

Packed and ready to ship

In contrast, the team responsible for the house called SYSTEM3 reduced on-site assembly almost to its absolute minimum. Designed by Dornbirn, Austria−based architects Oskar Leo Kaufmann and Albert Rüf, the house is an elegant spruce box 38 feet long, 15 feet wide, and just over 8 feet tall. It arrived at MoMA from the fabrication site in Reuthe, Austria, in two halves, each in its own shipping container. One container transported the completely preassembled "serving" unit, which provides the house's infrastructure, such as mechanical and electrical spaces, the kitchen, and the bathroom. The second container held only planar elements, including the floor, the roof, and walls. These components, flat-packed with the necessary fasteners and assembly tools much like an Ikea bookcase, were put together on-site to form SYSTEM3's "naked" space-the half of the house defined only by the inhabitants' furniture and devoted to activities like sleeping and dining.

 

The SYSTEM3 House (above) was shipped from its production facility in Austria (below) in two containers. Photos © Adolf Bereuter; diagram: courtesy Kaufmann/Ruf

 

 

The exterior walls of the serving and naked units are made of single slabs of 4-inch-thick engineered wood. Although the slabs had been CNC-milled to tolerances within 1 mm, Kaufmann and Rüf had concerns that the elements would not fit together once they arrived at MoMA. They worried that changing temperature and humidity levels during the trans-Atlantic voyage might cause the slabs to warp. And they worried that such deformation would cause collateral damage, such as cracking of the factory-installed windows. However, the containers arrived at the site at 6:30 a.m. on June 23rd with their contents in pristine condition. And by early afternoon, the last element, the SYSTEM3 roof, had been hoisted into place. "It was almost like they practiced in Austria," says Gorman.

 

One transported the completely preassembled "serving" unit, which includes mechanical and electrical spaces, kitchen, and bath. The other container held flat-packed planar elements. The assembly team joined the two types of components on the MoMA lot, completing installation in just a few hours. Photos © Adolf Bereuter

 

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High-tech cocoon

 

In the 75-square-foot Micro Compact Home (foreground), every space performs double duty. The bed folds down over the dining area (below), and with the door closed, the entrance becomes a shower. The unit incudes a kitchen, a toilet, LED lighting, and flat-screen TVs. Photos: © Dennis Gilbert

 

The only house that was faster to install was the diminutive Micro Compact Home, or MCH, for short. At just 75 square feet and 2.2 tons, the timber-framed, aluminum-over-plywood-clad MCH [record, April 2007, page 165] was transported from its Uttendorf, Austria−based manufacturer by container ship and then by pickup truck to the MoMA lot. The installation team secured the unit's three-legged base to its foundations and connected it to a power supply in less than four hours.

Horden envisions a vertical village of MCH units. Photo courtesy Tim Wessbecher

The cocoonlike MCH is intended to provide "short stay, smart living" for one person, or 1.5 people counting the occasional guest, according to Richard Horden, a principal at London-based Horden Cherry Lee. Horden, along with Munich-based Haack + Höpfner Architects, designed the house.

Inside the MCH, every space performs double duty. For example, the bed folds down over the dining area, and when the door is closed, the entrance morphs into a shower. The house also includes a kitchen, a toilet, and two flat-screen televisions.

The 8-foot-8-inch cube not only has a minimal physical footprint, but also a small carbon footprint. Taking into account appliances, LED lighting, air-conditioning, and heating, the unit would require about 86 square feet of PV panels and a small wood pellet stove in order to operate off the grid in Central Europe, according to Horden.

The MCH is already commercially available for about $78,000, and 15 units have been produced to date. Seven are being used for housing at the Technische Universität of Munich. Horden, who teaches at the school's department of architecture, stays in one two nights of each week.

The MCH could be grouped or clustered to form a high-rise or a Family Compact Home (FCH). For the single-family version, Horden suggests that children have their own units, complete with kitchen. "So that they learn to manage on their own," he says, reminding us that the cute cube has a serious agenda. "There are social implications," he says.