Prefabrication experiments - 65 - Concept Environment inc: the «modern» doublewide

Dimensional coordination and modularity of construction materials can be attributed to transportation standards or measures. This standardisation is especially true of modular buildings and shaped the emergence and proportions of the mobile home. The standard eight-foot wide trailer home could be pulled behind the average automobile. This dimensional optimization lacked spatial versatility and evolved to ten and twelve-foot versions enhancing versatility and adaptability as transportation capacity progressed both in terms of vehicles and infrastructure.

The eight, ten and twelve-foot singlewide caravan was deemed inflexible. Furthermore, its employment as temporary housing connoted a substandard quality.  To dispel mediocre undertones and further enhance three-dimensional adaptability of the modular home, the doublewide proposed the siting and stitching of two juxtaposed singlewide modules. The doublewide became a typical version of today’s manufactured homes including the familiar accessories such as a pitched roof, covered canopy and window shutters. The majority of manufactured home producers acquiesced this model of production to rival traditional construction by building traditional facsimiles.

Fringe experiments challenged standard production and strived to link factory production with a progressive aesthetic. Concept Environment inc’s take on the doublewide embodies the dream of linking housing manufacturing and modern architecture. This «modern» doublewide incorporated the elements of mid-century modern: horizontal sightlines, floor to ceiling windows, and open living spaces. The two twelve-foot wide modules were supported on thick, vertical plane, foundation walls rising from the site elevating the modules one storey off the ground. Freeing the ground plane was reminiscent of LeCorbusiers five points of a new architecture.

The kit included factory-finished modules delivered for assembly with site services, infrastructure and foundations arranged on-site. The wood framed «truss» modules employed platform framing: two by four walls and floor joist construction for the floor and ceiling. This version of modern modular proposed a potentially different path for prefab architecture; one of simple modern aesthetics. In general, the traditional aesthetic gained a foothold that it did not relinquish. Concept environment inc’s unique non-traditional design showcased modular construction as a versatile construction strategy both in the factory and for a diversity of placement features. The isolated living spaces above the ground plane could be a site specific or site indefinite architectural device in one simple gesture.

Concept Environment inc. double wide 1969

Prefabrication experiments - 64 - Monolithic thin shell domes

The relationship between industrialisation and building was founded on three principles: repetition, efficiency and quantity. The search for efficiency and innovation was weighed against traditional wood or masonry construction. Although industrialization offered speed and new methods, building culture related and still relates to slowly evolving trades, materials and methods. In order to rival traditional techniques and crafts, industrialization aimed to lower costs either by repeating processes, components and assemblies, by producing progressive experiments or by challenging traditional shapes and architectural types.

The classic dome or circular arch structure prompted experiments in almost every material: pre-cut geodesic skeletal or panel structures, fold-up domes, assembled shell segments and sprayed domes.  The dome’s legacy as a robust form resistant structure was conducive to prefabrication; it could be engineered simply. Wallace Neff’s bubble houses are an example of domes used for housing. Neff’s Domes were cast over inflatable plastic moulds known as bubbles. Each dome could be a single housing unit or juxtaposed to form an aggregated cellular housing structure. The inflatable moulds were light, transportable, generated no waste and required few man-hours to erect.

Neff’s techniques were further developed and commercialized by David South.  South’s monolithic thin shell dome structures employed and some still employ an inflatable polymer-based form or shape. Similar to the earlier Neff experiments, air pressure keeps the dome’s shape in tension during the moulding or spraying process. The domes are produced by spraying either thermosetting resins, light air-entrained concrete, polyurethane expanding foam or both a urethane layer and a concrete layer. The thin shell hardens and cures to a strong thermal resistant half-sphere. This type of monocoque dome employed one trade and simplified the complex procurement process that came along with building a traditional structure.

The interior surface could be finished with a cement-based coating or painted while the exterior surface of the dome could be covered with a UV protector or also finished with a cement-based coating. Available in multiple diameters, the domes were built in any context and for a diversity of uses. The dome has crossed eras and has proven to be a highly flexible structural system, however it has had less success as housing. The prismatic shapes of classical, medieval and modern architecture have anchored an aesthetic for dwelling that is difficult to sway from.

Left : Wallace Neff's bubble domes ; Right David South's patent drawings

Prefabrication experiments - 63 - Tunnel forms for poured concrete

Achieving visual quality, structural efficiency and long term durability in Concrete construction relies on three interrelated factors: the mixture and ingredients’ appropriate proportions, quality formwork and a monitored hydration process. An imperfection in one of these elements impairs the finished product, which is only revealed after it is complete. This makes quality control in concrete important but somewhat of a hit-or-miss. Conceivably the most demanding of the three constituents is quality formwork, as it is dependent not only on precise, robust and informed shapes and materials but on the workmanship of carpenters and steelworkers.

Developments in formwork, from vertical slip forms, to collapsible forms to tunnel forms and reusable forms, industrialized the production of concrete structures and made on-site construction more efficient. Although industrialization frequently connotes building in a factory, in the case of concrete construction, the construction site often becomes the factory. Particularly in slab and panel structures the site’s flexibility eliminates obstacles such as transportation and plant dimensions. Furthermore, hydration and curing time requires large spaces and produces a logistical issue in the factory or on the factory’s site.

Tunnel forming is a particularly efficient process as walls and floors are poured in one single step. This type of formwork came into productive use during the second half of the twentieth century, notably in relation to France’s concrete building culture and its important social housing projects. Tunnel forming uses an inverted u-shaped rectangular prism. Juxtaposed form-units generate inhabitable shelf-like spaces. The U-shape allows for vertical and horizontal planes to be poured at once. Rectangular Spans vary from 5-6 m in width to 10-12 m in depth with an approximate thickness of 200mm. Once preliminary hydration is completed and the concrete reaches necessary strength, the tunnels could be moved, raised or glided into their new position.

Patented in 1974 by the Societe Outinord-St-Armand (US 3979919 A), their system for a mobile a prismatic form combined the advantages of slip forms with tunnel forming to produce repetitive units transferring the advantages of mass production to the construction site. Although this repetitive building was not what modernity sought out for it to become, an answer to society’s problems, it did however influence an on-site factory model for concrete construction.

Patent drawing from patent US 3979919 A

Prefabrication experiments - 62 - Sekisui Chemical's Sekisui Heim M1

Japan's early production of prefabricated houses somewhat mirrored the prefab housing industry’s developments in other nations. Daiwa's prototype production of the «pipe house» in 1955 or its light steel framed «midget house» in 1959 was based on frame systems similar to 19th century British Iron house kits or American wood panel kits. Stimulated by an urgent need, Japan’s post-war housing programs encouraged both industrialization of housing and mechanization of production methods and established Japan as a major innovator in the industrialized building sector. Along with government support, the traditions of wood frame joinery, post and beam construction, and modular grid compositions both tatami and timber-based, combined to create a fertile context for prefabrication. This context was further augmented by mechanisation and a culture of renewal, creating one of the most advanced prefab building cultures on the planet.

Japan is recognized for its innovative production methods: from lean construction to mass customization strategies, to factory automation and to the industrialisation of building methods. The flagship producers such as Daiwa, Misawa, Panahome and Sekisui Chemical have contributed to the industry’s evolution from post war mass production to today’s high quality fabrication combining efficiency and customization.

Sekisui chemical produced its first modular light steel frame box-unit in 1971: The Sekisui Heim M1. The box-unit’s commercial success contributed to lowering its construction costs and an increased production capacity and addressed the continuing modern dream of a factory-produced house (over 18 000 were sold). The basic module unit was a rectangular prism composed of light-gauge steel framed edges, which were infilled with walls, floors, ceilings and service cabinets. Multiple cabinet organisations were offered demonstrating the early stages of mass-customization strategies. Each box-unit could be juxtaposed or stacked with complete box-units or with partial units (2/3 of a complete unit). The coupling of structural edge members simplified the stitching of adjacent units.

The 2.4m x 4.8 m box-units were based on a 2:1 ratio reminiscent of a tatami floor mat. Each house included a special tatami room relating to traditional Japanese housing. The system’s suppleness, in plan and in section, challenged the mass production paradigm that defined most prefab construction systems. Sekisui’s combination of industrialisation, variability and tradition prompted a new era for prefab architecture.

Box unit axonometric from Sekisui Chemical's advertisement