Prefabrication experiments - 472 - A Perfect Storm for Mass Timber

 

Selected materials and construction strategies embody the era they are invented in. Pozzolanic ash concrete provided Roman builders with an artificial stone to erect vaulted and domed structures that still stand today. Industrialization harnessed new energies for steel and concrete elevating construction capacity for edifices of scopes, sizes and heights impossible to imagine before then. Reinforced concrete, a robust and intrinsically fire-proof material, came to represent the modern industrialized housing block. Casting this malleable and resistant material into shapes reformed onsite construction as surface elements for floors, walls, roofs, and other required components like stairs or balconies could be precast in quantities offsite, delivered and easily assembled onsite. The precast large panel blocks of postwar France epitomize the marriage of a material's properties and overwhelming demand for its use. 

 

Today, critical decarbonization of building activities to reduce construction’s environmental footprint, increasing urbanization and a demand for quickly built housing is stimulating the demand for another twentieth century material:  engineered laminated timber. Both glulam and cross laminated timber are embraced as eco-friendly as their low carbon footprint when compared to energy intensive materials like steel or concrete has unveiled a competitive edge in the age of rapidly evolving climate change. 

 

Engineered laminated mass timber is relatively simple to produce, and components can be fashioned in any geometry and precisely cut as customizable offsite produced kits for building. Parts, slabs, panels, columns can also be normalized or standardized according to spans and dimensional requirements of reproducible building types. The Sylva scalable timber construction system by European forestry company Stora Enso demonstrates the straightforward mass timber approach: post and beam glulam is complemented by cross-laminated elements for bearing or spanning elements. Along with their school kit, Stora Enso produces components ranging from simple linear elements to comprehensive modular volumetric building sub-assemblies to be stacked into multiple configurations. Along with sequestering carbon during their lifespan, if the timber is protected adequately and its joinery designed for disassembly, components can be deployed over multiple lifecycles, making mass timber perfect for low embodied energy building.

School ConstructionComponents by Store Enso

Préfabrication experiments - 471 - From assembly lines to trucks, ships, trains and helicopters

Manufactured dwellings are idealized for efficiently supplying homes delivered from a factory to any site. Mobile homes built on standard-sized steel trailers were designed, robustly built to be pulled over roads and adapted to common towing devices. Modular volumetric buildings use similar manufacturing principles, without the mobile substructure, and require flatbeds to carry the volumes to their site, where they are lifted to be set into their final position. Cranes equipped with spreader beams, used to strap the modules, make easy work of modular assembly. Both approaches, a steel mobile trailer or an independent volume, are defined and constrained by transport loads and dimensional parameters.

 

Getting these factory-produced buildings to remote locations sometimes requires more complex logistics; Cargo ships can be used for intercontinental transport. Stacked on ships, they can be rolled off or craned onto barges to be brought to ports and then trucked to their final destinations. Rail is also possible, however it is considered less convenient as the modules would have to be lugged to and from rail lines as manufacturing facilities are not necessarily located in proximity to railway networks. 

 

Another form of modular transportation has been imagined to get houses to any location. While impractical, complex and expensive, the dream of flying a house is connoted in many prefab experiments. But is it really feasible ? High-capacity helicopters, such as the Sikorsky S-64 Skycrane, Boeing CH-47 Chinook, and the Russian Mil Mi-26, are known for their exceptional lifting capacities. These helicopters are specifically designed for lifting and carrying loads exceeding 20,000 pounds (9,072 kilograms). A standard modular volume 12feet x 40feet can easily weigh up to 20 000 pounds. While lifting and delivering one unit is certainly possible, assembling a building in this way is unfeasible. 

 

Whether truck, rail, ship or helicopter, modular volumetric construction is regulated by its factory manufacturing on an assembly line which also determins maximum width as in all cases the module will have to be trucked from its production area to a staging area before its final transport. 

Sikorsky S-64 Skycrane (above); Boeing CH-47 Chinook (below)

Prefabrication experiments - 470 - Soft densification and pre-approvals

 

Industrialization has certainly sped up production of every commodity and reduced their cost per unit. In an era of urgency, housing promoters were inspired by advances in manufacturing. In the wake of World War 2, the subsequent population growth and economic boom of the «Trente Glorieuses», suburbanization and development were linked to the automobile’s democratization. Bedroom communities planned with small uniform houses sprouted using assembly line principles. Along with housing, strip malls, and schools deployed similar modular planning methods in a generalized sprawl of mass-produced built form. 

 

Vast building initiatives consumed resources and quickly reorganized the live-work relationship around commuting. The current climate crisis reframes postwar suburbanization's dwelling provision strategies as wasteful and is providing a context for these bedroom communities to be reimagined as land reserves for soft densification in response to the need for affordable housing. As was the case in the first act of suburban building, communities are again turning to industrialization to quickly provide replicable housing types. To skip over some of the time-consuming permitting and planning associated with one-off projects, catalogues of preapproved designs that add-on, retrofit, or provide accessory units on existing tracts are an attempt to increase housing supply and curtail uncontrolled sprawl.

  

The town of Collingwood in Ontario, Canada has initiated a streamlined ADU (accessory dwelling unit) permitting process based on pre-approved designs, financial incentives, and landlord support tools for ADUs marketed as rental units. ADU’s can be delivered to backyards, attached to an existing structure, or included within the main dwelling unit. The designs are intended to ease design decisions and procurement. One of the preapproved designs is a a 516 sq feet modular volumetric unit, a design by Habitat 28 and Attimo Homes, engineered-to-order and delivered to any site circumventing the usual permit process. A streamlined procurement timeline includes client, permit department, fabricator and builder; this type of integrated supply chain of actors can certainly decrease housing supply challenges using industrialized building systems geared toward repurposing underutilized land resources.

Plan of the P50 by Habitat28 and Attimo Homes

Prefabrication experiments - 469 - Platform theory for scaling efficiencies

 

The current affordable housing crisis is driving policies for change in the construction industry and its supply chain sectors. Necessary steps toward efficiencies include reducing bureaucracy, increasing productivity and performance; Performance framed by climate change, requires low-carbon building solutions while increasing supply. Factory production using materials and methods that harmonize quality, quantity along with reducing construction's wastefulness and environmental footprint is promoted within the future of construction road maps toward decarbonization in many countries.  

 

Manufacturing principles can be deployed to increase efficiencies and have proven their worth in all industries with building construction lagging. Industrialized building has had some successful applications in architecture; modern timber, steel and concrete construction systems were directed to solve the housing crises of the interwar and postwar years. 

 

Timber framing used in tract housing, most notably in Levittowns, is a case in point where sawn lumber was dimensioned consistently and deployed to an incredible number of houses using similar spans, plans, and elements. Dimensional consistency within a well-established and understood supply chain is what made timber framing so scalable. The same type of scalable normalization was used in steel buildings for large hangars or storage facilities. Panelized reinforced concrete also used material normalization to become a formidable, industrialized building system in Europe. All three construction methods can be described as «platforms» geared to particular types; small spanning timber for houses, large-spanning steel for industrial buildings and fireproof concrete for multiunit buildings. 

 

Still, the one-off nature of the construction industry impedes the scalable standardization in supply chains required by manufacturing.  Industrial production applied to building calls for a comprehensive transformation toward an integrated process with platform theory at its core. Using the same platform - type relationship that led to the above-mentioned successes in processes and designs should be directed toward consistency in building design and production. Further cross-sector collaboration between manufacturers should be based on normalization to share challenges and offer opportunities for best practices to be streamlined throughout the industry. This would allow one-off singular projects to be based on repeatable details, components and manufactured elements - developing a mass-customizable approach in construction. 

Top left: Levittown mass production; bottom left: Typical concrete panel block; Right: a platform for combining residential spaces into diversified designs (Resolution 4 architecture)

Prefabrication experiments - 468 - Flexibility of on and offsite reinforced concrete

Whether cast on or offsite, reinforced concrete construction was generalized for collective housing in a relatively short period between the end of the 19th and the middle of the 20th century. Prized for its rapidity, strength, flexibility and fireproofing, the malleable material also sustained the invention of new industrialized building systems and their architectural potentials. Slabs and columns could take rationalized form-resistant shapes and heights difficult to achieve in conventional timber or masonry construction. Further, the open plans based on a rigorous grid of distanced posts or columns generated horizontal arrangement fields free from the structural constraints of customary bearing walls. Massive postwar rebuilds throughout Europe contributed to understanding the possibilities for these systems to be mass-produced and modulated for any context. 

 

In Italy during the late 1960s and early 1970s many collective housing blocks were erected by fostering the advantages of reinforced concrete with precast elements. Italian architect / designer, Angelo Mangiarotti planned a series of collective dwelling blocks which showcase the shared knowledge maturing in multiple countries. Born on February 16, 1921 in Milan, Mangiarotti graduated in architecture from the Milan Polytechnic in 1948. He met modern masters Frank Lloyd Wright, Walter Gropius, Mies van der Rohe and Konrad Wachsmann as a visiting professor at the Illinois Institute of Technology in Chicago in the early 1950s, where prefabrication was extensively seen as the future of architecture and construction. 

 

After returning to Italy, Mangiarotti founded a studio, and investigated a building system that combined onsite cast concrete flat slabs with a modular precast curtain wall system hung from the perimeter of the concrete floors. Based on a strict modular grid, factory-made opaque or transparent vertical panels would simply slide and suspend from a horizontal modular lintel block anchored to the main structural slabs. A compositional interplay of vertical panels and windows varied the arrangement according to any customizable layout within the adaptable open plan. This hybrid onsite and offsite system was stacked to 8 stories at Monza from 1968-1975 and 5 stories in Arosio contributing to the rebuilding of Italy and defining the country as a locus for the study of flexible open prefabrication.

Edge detail of the suspended curtain wall

Prefabrication experiments - 467 - On and off-site Supply Chain Overlaps

Supply chains in building construction involve multiple project stakeholders, trades, and contractors charged with completing a building. Offsite construction implies harmonizing two diverse supply chains that overlap through final assembly. An electrical contractor hired for wiring and finishing a building chunk in the factory is often organized differently from the contractor that is then mandated to complete connections and coordinate the work on site. 

 

Trade duplication and imbrication can increase costs associated with sitework even if factory production is optimized. This is just one example of the complexities associated with harmonizing onsite construction culture with factory manufacturing. Professionals, suppliers, general contractors, inspection firms, specialized trades are contracted on a project-by-project basis, at worst chosen according to a lowest bid system or at best employed from project to project to harness some iterative traction. Moving from this type of fragmented ethos to an integrated manufacturing process argues for replication and product standardization: Deploying similar products, people, coordination and spreading costs over multiple projects.

 

Successfully reaching time and cost savings is contingent to bulk purchase orders for everything from surface materials like ceramics or drywall to plumbing pipes, sinks and fixtures. A scalable supply chain tuned to an ascertained output is the basis of industrialized production and should inform onsite construction management. Normalized grids, patterns, designs and details can facilitate and maintain a symbiotic relationship codifying assemblies and tasks.  

 

Occasionally compared to automobile manufacturing, furniture production or even shipbuilding, building is distinct from these products in its durable (50-100 years) anchoring to a particular site. This implies at the very least differentiated connections to infrastructure, foundations and structural specificity determined by locus criteria; constraints that impede complete reproduction as is the case of other commodities. Fine-tuning these two fields of production with their underlying supply chains remains one of the greatest challenges to prefabrication’s uptake; Contemporary design tools and digital twins are facilitating information exchange an important element for increased collaboration and potentially streamlining supply chain decisions. 

Clyde, Shu and alt. (2024) Offsite Construction Supply Chain Challenges: An Integrated Overview. 

In Journal of Construction Engineering and Management

Volume 150, Issue 7

Prefabrication experiments - 466 - Transport challenges

 

Archigram’s flying house, blending a mobile home with a high-capacity military grade helicopter, and Paul Rudolf’s classification of the mobile home as American vernacular define the complex relationship between the industrialized production of homes and architecture’s evolving perception of the low-cost factory built dwelling archetype. Architects have generally understood and promoted the arguments for manufacturing architecture in a streamlined, quality-controlled setting, delivering a 99% complete fabricated house to a client, however, transportation constraints and normalized outputs have been criticized for their inflexibility.

 

Modular volumetric construction seeks to reform this long-lasting friction by stacking premade customizable boxes, using the manufacturing lessons learned from the mobile home to make large-scale unique buildings. 

 

Whether mobile, manufactured or modular, the same underlying constraints that led to the 12’-wide homes and progressed into 14-foot and even 16-foot-wide modular boxes requiring special permits and chaperons, transport is the number one design criteria limiting modular volumetric’s formal diversification. Large scale chunk delivery limits spans, codifies metrics, and requires structural redundancy to make the large volumes robust enough to withstand rolling and bumping over long distances. 

 

Once delivered to their final destinations, the factory-finished boxes also imply large staging areas and cranes to set them in place to be stitched and weatherproofed. Long distances can also be prohibitive, remote locations, or even dense urban environments, all requiring increased logistics and special permitting for temporarily blocking traffic in tightly packed urban settings. Volume height is equally limited by overpass clearances making anything over 8-foot interior tricky without using low-bed vehicles. Notwithstanding these procedural challenges, the factory-finished large boxes sometimes up to 60’ long make quick work of any residential building as 12 x 60-foot modules can be carried on flatbed trucks requiring no special permits.

 

Transportability has long been highlighted as a central narrative in prefab architecture representing the freedom afforded by the moveable house able to adapt to any context, brought to site by road, sea or air supplying buildings as commodities ready to be used without the headaches of conventional construction.

top left: House 19 (Korteknie Stuhlmacher) ; top center: Sikorsky Sky Crane delivering a home ; right: UFO house carried to its site ; bottom left: The Flying House ; bottom center - modular buildings on a barge

 

Prefabrication experiments - 465 - Factory building and Buildings

Currently, making building chunks in a factory deploys all manner of numerically controlled cutters, routers, cranes, panel bridge nailers, butterfly tables, and conveyors to increase offsite construction's capacities and value. Uptake in all sectors of construction’s industrialization is being stimulated and directed by these digital tools and techniques along with their underlying data. The principles of factory production applied to architecture can reduce waste at all levels of the building process functioning in a climate and quality-controlled environment. The invisible hand supporting factory production is standardization. Replicable elements and processes increase scalable efficiencies. Cutting, organizing, assembling, and packing in a covered space stresses how Fordisms and Toyota-isms (lean construction) can be arranged for producing edifices. 

 

While the tools have been updated with the objective of increasing productivity, the primary elements of a factory remain the same.  The Ford Motor Company factories as designed by Albert Kahn at the end of the 19th and beginning of the 20th centuries promoted an open system, with spanning elements supported by small and vastly spaced vertical bearing elements. Reinforced concrete, steel and timber examples all traced a similar path; the roof or covering plays a fundamental role in orchestrating a malleable choreography of materials, machines and people to achieve a streamlined process from receiving components to the delivery of value-added assemblies. Logistics are comprehensively protected from climate and other contextual difficulties imposed by conventional job sites. 

 

The factory can be permanent or temporary (flying factories) structured by the posture of protection and an ideal of adaptability. While the interior arrangement of equipment can change, the building system itself is a generic support structure where a robust slab supports floor equipment and robust beams or girts suspend tools, creating ideal horizontal planes delineating a secure manufacturing environment. The architecture produced in these environments is normalized and of greater quality than projects built onsite as systems, details, assemblies are perfected gaining knowledge from product to projects. Cleanliness, organization, process geared spaces of production are an important part of construction culture, whether prefabricated or site built; iconic temples of mass production hangars protect and generate efficiencies for better buildings.

Ford Motor Company Long Beach Assembly Plant, Assembly Building, 700 Henry Ford Avenue, 

Long Beach, Los Angeles County, CA

Library of Congress Prints and Photographs Division Washington, D.C. 20540 USA

 

Prefabrication experiments - 464 - Catalogues and pattern buildings

 

As housing demand increases and supply festers because of aggravating construction challenges, policy makers are surveying offsite construction as a quick fix to a systemic problem. Housing provision is not only related to productivity but should also address changing lifestyles, demographic fluctuations, and affordability which require comprehensive governance beyond design and production. The catalogue of housing types and the pre-approved pattern building have been proposed as potential avenues for boosting supply. 

 

The catalogue was explored by Canadian housing authority (CMHC) in the 50s and 60s and led to the construction of many homes responding to the post war baby-boom. Architects were given an opportunity to contribute archetypes for the nuclear family in a suburban setting. Articulated to house similarities private industry developed high levels of standardized designs and construction strategies. While not prefabricated, the catalogue certainly pushed low value-added industrialized components in every suburban tract; the timber platform frame was abundantly used. 

 

Similar normalization and socialist policies in post-war Europe deployed reinforced concrete precast panels as the system of choice for replicable collective blocks. The «pattern» large panel edifice was an exercise in standardization akin to the single-family dwelling but with the added value of serializing a kit-of-panel elements to be used en-masse. Both systems, lightweight timber and reinforced concrete, were made affordable by their large-scale use. The catalogue and the typical block directed straightforward solutions to housing supply - repeatable designs that could be patterned and predetermined to harmonize supply chains economically federating all required materials and methods. 

 

Critiqued over and over, today this regularity, while not a comprehensive solution to the current housing crisis is being promoted once again arguing that housing provision is slowed by design and approvals; remove architects from the planning process, simplify permitting, its associated delays, offer model buildings, and housing will go up quicker. This type of short-sighted planning is partially what killed prefab’s potentials through enduring prejudices.  Supporting creative initiatives toward innovative and affordable solutions for contemporary needs, may take more time to develop, but the current crisis requires a holistic approach to avoid offsite bearing blamed once again for systemic challenges. 

Left: CMHC catalogue design by R.T. Affleck ; Right: Pattern large panel blocks for a new town (USSR)

Prefabrication experiments - 463 - Lessons from the mobile home sector

Critiques of the mobile home industry range from suspect construct quality to cookie cutter inferior design and to trailer parks denoting less than ideal living conditions. While these assessments have been debated, the production of these untethered shelters on an assembly line can certainly relate expertise about dwelling affordability. 

 

The self-built inhabitable trailer and the manufactured house, a progression of the mobile home, share the chronicles of building a whole or half of a house on a mobile steel chassis. The chassis, a movable foundation platform onto which the home's structure is attached, also facilitates rolling the structure in the factory from one production station to another. The mobile home differs from modular volumetric building chunks which are usually produced without the steel wheeled base, installed on a permanent foundation, carried on a truck and stacked multiple stories high. Both share the benefits of completing most building tasks in a climate-controlled setting.

 

For a typical onsite built house, labour can represent up to 50% of total costs; factory workers' reduced wages, automated manufacturing, assorted aids such as hoists, jigs, automated machinery and gantry cranes can reduce labour costs by as much as 30%. The repeating patterns of mobile homes also make it possible to make bulk purchases for everything from wall board to kitchen cabinetry and plumbing fixtures. With all these cost rationalizing measures, the mobile home industry still represents a successful segment of home production accounting for roughly 9% of all homes built in the US. 

 

One of the important lessons of the inhabitable trailer is the in-factory optimization integrating experience from home to home reducing task times and waste at every step of the process. When compared to onsite construction, quality control in the factory and inspecting recurring designs and organizations is simpler - fostering clear procedural practises. Founded on the strengths of mass production, most companies offer predetermined designs with some options for customization, however product seriality whether based on linear or cellular manufacturing lines is the formidable lesson that can be learned from mobile homes. 

Star Mobile Homes advertisement