Prefabrication experiments - 112 - Structures - 3 - The Butler Frame

The production stages linking resources, materials, component manufacturing, structural systems and quality control underly the principles of Offsite construction and industrialized building systems. Simplified on-site assembly of pre-engineered components require a rational design, engineering and production process. Steel construction and frame structures have typified this relationship.

Steel frame construction is a straightforward assembly of hot or cold rolled structural profiles in assorted shapes and sizes. Each component is manufactured and catalogued and can readily generate skeletal structures that offer flexible planning and perform according to their engineering.  Steel construction has related to off the shelf assembly since the early 19^th century. Henry Robinson Palmer patented rolled corrugated iron in 1820, which became a staple of many dry construction kits exported to several British colonies.

In the vast field of steel construction, the Bulter rigid frame depicts steel's relationship to pre-engineering. Patented in the early 1940s by the Larkin brothers, owners of the Butler manufacturing company, the frame structure became the basis of the company's large line of engineered building kits. Their objective was to offer a manufactured hangar type building to supply a growing need for industrial structures.  Somewhere between a portal frame and a gable frame, a series of aligned frames composes a simple shelter. The pointed arch structure employs rigid connections at each junction reducing and countering beam deflexion associated with large span buildings.

The moment/rigid connections between column and rafter counter lateral loads and create an open space that could be organized in plan and section with little restrictions and without bracing. The chamfered vertical columns along with the chamfered rafters express material rationalization: a schematic of structural efficiency. Greater spans are achieved by simply increasing material sections.

The rigid frame is anchored to standard strip foundation walls. The streamlined shape is still available from Butler Manufacturing in various sizes and spans from 60 – 300 feet. A metal building insulated panel complements the easy to erect Butler frame kit. Engineered buildings remain popular within industrial and commercial applications, but rarely for any type of architectural use. The pre-engineered prototype offers high value as it is both pre-manufactured and pre-engineered optimizing a potential quick maneuver from product request to on-site assembly.

Butler Frame undergoing laboratory testing

Prefabrication experiments - 111 - Structures - 2 - Form resistant structures : the thin shell

A shell structure or a thin shell structure is an organizational system that uses its shape or form to optimize its capacity to withstand external loads. Based on similar principles, the classic arch in building construction or the egg in nature, distribute material outward throughout their surfaces in order to counter external loads. The catenary arch as an inversion of tensile structures toward purely compressive shapes invokes the basic ideas of form resistant structures: shape or profile opposing load.

Emblematically used by Felix Candela, reinforced concrete shells’ mathematically informed curvatures harnessed tensile and compressive stresses as the basis of structural integrity. Reinforced concrete was the flagship modern material for thin shell construction and helped produce avant-garde works of art. Although concrete has been employed both on-site and off-site, the use of polymer composites has entertained the most recognizable relationship between prefabrication and shell structures. From the Monsanto experimental plastic house to Arthur Quarmby’s experiments on railroad service buildings, the thin shell has complemented plastic composites to exemplify lightness, form resistance and a tangible capacity to be easily manufactured and assembled on-site exemplifying a type of commodity architecture.

Matti Suuronen is unquestionably the most notorious of the many architects that have explored the glass reinforced plastic thin shell structure in regards to its potential industrialization for mass produced architecture and housing. The composite shell synonymous with this type of architecture was made up of a glass-fibre reinforcing textile encased in a hardened polyester resin. Analogous to fiberglass boat hull production, the interior and exterior glass reinforced layers usually covered a hidden layer of expanded polyurethane foam insulation, which gives the shell its insulating properties. These types of shell envelopes have been used in diverse settings as they are both light and flexible. Suuronen’s UFO house and his Venturo house are prime examples of thin shell structures applied to mass-produced architecture. Less monumental then their counterparts in concrete, the plastic shells are nonetheless prototypical. The Venturo house further explored the thin shell volume as a plug and play component of community building as its plastic modular parts and overall shape could be easily assembled to create multiple housing organisations.

A potential combination of three Venturo houses

Prefabrication experiments - 110 - Structures - 1 - The A-frame

Whether early post and beam, industrialized balloon framing or recent developments in engineered wood systems, timber has a tangible relationship with prefabrication as pre-cutting, boring, notching and defining members before their use is as old as building. Along with traditional woodworking, pitched log structures defined early timber framing and vernacular architecture in many forest-rich nations.

The simple dry assembly of vertical members into form resistant structures has given us the humblest examples of inclined roofs and maybe the most notorious associated with cabin building during the 20th century: the A-frame structure. Advantageously utilizing the stability of a triangular arch as the basis for a simple skeletal form, the A-frame is composed of two oblique members (legs), forming a simple isosceles or equilateral triangle. The legs are then joined, nailed or bolted at their vertex angle and retained at their center by a horizontal cross member or a tie beam, completing the «A».

Spread out and axially aligned along their vertex, a series of A-frames organize a simple and flexible unidirectional space with open gable ends. Employed as a prototype of the secondary home its simplicity still seems to fascinate designers, architects and self-builders; it is a structurally effective, aesthetically pleasing, and straightforwardly built structural system. Habitually braced by horizontal members or purlin beams each oblique portion of the triangular based prism is anchored to ordinary foundation walls. Clad in wood planks, metal laminates or even asphalt shingles the structural advantages of the a-frame were nicely complemented by potential costs-savings, as the pitched wall was at once wall and roof. 

The A-frame components can be easily transported and adapted to any context or topography. A-frame cabins popped up in diverse snow-capped and mountainous regions of North America exemplifying the era's fascination with both leisure and flexibility. The A-frame is a lasting version of an easily deployable dwelling. Self-builds, manufactured made to measure or made to order kits integrating the simple the A-frame continue to define simple prefab and relate this simple timber structure to the fundamentals of dwelling – a simple base or ground plane, a pitched roof structure and transparent gables that open to magnificent views.

Red A-frame, Far Meadows, California

Prefabrication experiments - 109 - The atrium house by Bengt Warne

The courtyard house as a prime example for single-family dwelling has endured. Arranging living spaces around a garden creates an intimate oasis positioning family life around a nature centric focal point. As was the case for the Roman atrium dwelling, the central garden can be used for gardening or socializing and can provide passive summer cooling using a central water element. The modern central patio prototype was proposed by architects such as Mies van der Rohe (court houses) and Jørn Utzon (Kingo Houses) and even Walter Segal’s courtyard houses as a pattern for densely aggregated individualized mass housing. This central courtyard model inspired an audacious proposal by Swedish architect Bengt Warne relating an archetypal space to industrialized building systems.

Designed as a luxury dwelling, Warne’s design, presented in 1961, combined prefabricated prismatic volumes around a central void covered with an articulated glass roof. The organisation was based on a 4 meter square grid which defined an 8 x 8 meter square patio. Prefabricated in a re-deployed shipyard the perimeter box volumes were structured by steel profiled edges. The four 12m x 4 m x 3m tall enclosures were fitted together on standard foundations and stitched together on-site as all other finishes were completed 700 km away by the AB patio company. On site assembly lasted only a few hours including the electrical connections for the mechanical roof canopy. Exterior infill panels and glazing reduced potential thermal bridging of the steel mullions. Simply organised, the heroic element is the electrically controlled articulated petal roof spanning the central void. Driven by 4 hydraulic jacks the triangular deployable roof transformed the interior space into an outdoor terrace.

The prototype was built as a 256 square meter single family home and was to evolve through mass production into a smaller 144 square meter version at an affordable cost. The major difference between the original prototype and the mass produced model was a reduction from 16 meter square to 12 meter square. As with many modern prefab experiments, the mass production of the atrium house never took off but it nonetheless activated a career-long exploration by Warne into a series of ecofriendly homes.

Photograph of deployable roof