Prefabrication experiments - 531 - The Modern Long Building

At the end of the 19th century, industrialization, mass production, new materials and housing shortages converged to foster new building systems and types. Light timber housing in the form of balloon frames, steel skeletons covered in glass for tall buildings and intrinsically fireproofed reinforced concrete gave us the collective urban housing block. All three types, framed by construction methods, were also inflected by the broader reforms that were arising in society. New city patterns were shaped by these methods, suburbs sprouted with small houses in balloon and later in platform framing, and perhaps no urban environments were reshaped more than those spawned by the reinforced concrete block or slab building. These included some «mega» examples inspired by perceived assembly-line rationalizations applied to housing. Three examples, in Italy, Germany and France demonstrated the way these new buildings would be developed as autonomous urbanities.

Wartime propaganda led to Clemens Klotz's Colossus of Prora (1936-39) in Germany, (original design of 4,5 km in Rügen near Binz) planned as a leisure seaside retreat to keep the population loyal to the fascist regime through the concept of Strength Through Joy. France's Les Courtillières Serpentine building (1 060 m, in Pantin near Paris) designed by Émile Aillaud broke ground in the 1950s (1957-67) as part of the country's large-scale postwar building program and positioned flats in a curvilinear pattern that could conceivably go on endlessly. Not to be outdone, Italy's 1-km-long example in Rome (Corviale or Nuovo Corviale, 1975-82) designed by Mario Fiorentino was likely inspired by LeCorbusier's Slab buildings. All three express 20th-century modernism relating affordability with densely packed urban slabs, and quality of life with placing these buildings in large public gardens or scenic landscapes. Further their multifunctional infrastructures would generate economies and maximize social interactions between inhabitants.

While certainly an expression of optimized, serially designed dwelling systems, these megastructures came to connote a sameness and alienation. Located far from urban centres with inadequate services made most of these modern structures an argument against this type of dense urban living which and the underlying principles of modernism. Notwithstanding its negative aura, the long building remains one of the most iconic and optimistic representations of allying urbanism, construction systems, and assembly line principles in the pursuit of affordable housing.

left: Colossus (4,5 km); centre: Les Courtillères (1,06 km); right: Corviale (1 km)

Prefabrication experiments - 530 - PSSSHAK « Primary Supports Structure Housing Action Kits »

Separating common structural and infrastructure elements from interior non-permanent spatial systems has been posited by many as a way of providing a flexible framework for adaptable buildings that facilitate changes over time, responding to occupant evolution without destructive and wasteful demolition. The PSSHAK (Primary Supports Structure Housing Action) kit system presented to the UK government by a group assembled by John Habraken in the early 1970s deployed the author/architect's theories in a practical application for the design and construction of affordable housing. 

 

Structural walls supported a centralized organization with kitchens and baths defining interior zones within a rigorous row-house masterplan. The entire system was regulated by a 30cm grid to dimensionally coordinate the production of «kit» components. The grid also framed potential arrangements for users to organize their interiors while respecting overall design parameters, to at once engage occupants and implement coherence throughout the scheme. Linking design with fabrication and construction, the kit of parts strategy was developed to optimize logistics, material supply chains, construction methods, and procurement approaches as multiple projects would use these common elements and their mass production would generate economies of scale. 

 

Habraken underscored housing allocation’s complex process requiring efficiency and purchasing power for the collective while introducing freedom in planning personal systems for the individual or the household. Linking productive master planning and individualized microplanning remains a difficult challenge as the housing industry is dictated by a general-contractor or developer model that, in the name of profitability, will resist the progressive separation of supports and infill which limits their role to either common elements or to providing interior elements on a far more informal basis, cutting their margins. 

 

A system like PSSHAK requires a profound systemic transformation of the housing sector. It has been marginally supported with open building being implemented in theory but has proved to be challenging in practice. Habraken's theories behind the PSSHAK are today reframed by an era in which all housing stakeholders are looking to increase productivity and provide quality affordable housing.

Basic dwelling unit and its adaptable parameters

Prefabrication experiments - 529 - Underlaying modernism

Architectural modernity’s idioms sustained by industrialization envisioned a new formal language seemingly detached from any classical references. One concept perhaps above all others supplanted historic composition considerations and other preindustrial planning traditions: the industrially coordinated grid. Used as an underlayment for form and space creation, grids were deployed to shape uniqueness, detail modern construction and reject conventions. Mass production inspired material criteria as guides for rationalized design.

 

Grid compositions were not specific to modernism, both classic and vernacular buildings used dimensional planning aids to rationalize architectural designs or standardize material use: geometric proportions based on instructions such as the Golden Ratio, or the Ken in Japan predate modernism's fascination with patterns that drive designs. The grid in the modern era referenced industrial parameters or material production more than any other dimensional principle. Efficient factory supply drove many theories of dimensional coordination based on facilitating the conceivable interoperability of building components in a Design for Assemblyparadigm. The 42-inch or the 48-inch grid became the most recognizable canon of modern planning. Other frameworks were also determined by modern material choices: 20-foot spans for flat slab reinforced concrete, 8-foot singlewide mobile home volumes based on their transport requirements or even 16-or 24-inch stud placement in timber framing all related to fabrication logistics. 

 

Education also linked building design to preset mathematics to expedite its organization and to define the modern architect's planning doctrine. Grids used as coordination devices outlined simplified arrangements for everything from structural to spatial and mechanical dispositions. Mies, Eames, Prouvé, and Wright, the same architects who perceived in industrialization a means of reforming of architectural production became the masters of grid use and elevating industry's architectonic potential. Their careful use of square or rectangular grids was masterfully deployed to reveal spatial dynamics - sliding, aligning, juxtaposing or separating spaces. The grid was analogous to a musical score onto which elements were positioned as notes to create rhythm, symmetry or dissymmetry, axes - all classic elements of architectural planning - showcasing modernism’s claim to novel geometry was deep-rooted.

Grid use at Mies van der Rohe's S. R. Crown Hall at IIT (Illinois Institute of Technology) (1956)

Prefabrication experiments - 528 - Modularized mechanical systems

 

Modular volumetric construction requires more planning than conventional construction to reap its potential benefits of time and cost savings. On-site stitching details to guarantee structural and climatic performance are just the tip of the iceberg when it comes to the required systemic coordination. The rigorous design of connections and networks to produce code-compliant electrical, plumbing, and HVAC systems involves upstream, rational modularization. In a typical flat composed of two neighbouring modules, or two stacked boxes, connections to building systems are sectioned and capped, or in the case of electrical systems, cable lengths are provided to connect individual private dwelling systems to collective grids. 

 

Precise planning according to how modules will be positioned on site means that mechanical design and coordination is complexified with teams having to not just plan systems but also understand and manage manufacturing logistics for streamlined production and comprehensive functionality. In the best cases, the entanglement that is synonymous with on-site coordination is avoided or at least minimized as systems are planned as discrete components with efficient clear distributions and links. 

 

Access hatches, loose cable lengths, vertical service stacking, repeating mechanical distribution using corridors as runways and vertical stacked wet cores adjacent to pipe chases facilitate mechanical distribution. All system locations should be carefully noted and catalogued in the factory for onsite and future reference during building construction and operation. Along with professional cooperation and collaboration, strict factory management and control tools as well as DfMA digital software platforms for virtual design of systems networks aid in determining the most efficient paths for pipes, wires, ducts, equipment placement and optimal arrangements for onsite completion, without deconstructing what was efficiently assembled in the factory.  

 

While the upstream planning requires greater synchronization between professionals and builders, a repeating pattern of flats from floor to floor makes it easier to scale these strategies for connecting systems along with confirming all the code-required fireproofing and acoustic performance at specific modular touch points. This comprehensive and coherent modularization has multiple advantages for initial construction, but can also facilitate repairs, retrofitting, and replacement of elements during a building's lifespan. 

Organizing mechanical systems in a factory setting

Prefabrication experiments - 527 - Modular volumetric structural organizations

 

Buildings generated from modular volumetric construction in timber, steel, reinforced concrete, or from hybrid compositions of these materials follow two principal structural strategies: As the modules are self-supporting, the first simply stacks volumes; loads are distributed through their faces from one box frame to another. The second, architecturally iconic, employs a mega support structure onto which the self-supporting boxes are inserted as if carefully placed in a scaffold or on a shelf. The first strategy remains the path of least redundancy as having a mega structure has proven to increase costs, although it becomes necessary in tall modular buildings.

 

Without a secondary supporting rack, gravitational loads are distributed through bearing walls or vertical columns creating paths or grids analogous to those found in post and beam or wall and slab construction. In lightweight timber construction, module corners are sometimes reinforced with columns composed of 2-by stock or by using steel elements. As vertical loads are distributed through modules, lower modules bear the weight of the entire structure. In a six-story building, the lower volumes must be structurally more robust, which also implies a production management strategy to sequence and nuance production according to each module’s placement within the overall structure. 

 

Efficient structures are also contingent to alignment. All elements that are cantilevered or out of alignment, angled, or rotated complexify structural design and particularize the manufacturing of those design elements, which in turn increases costs. To account for horizontal loads and bracing, module walls and floors can be designed as rigid diaphragms active over multiple modules. In skeletal modular structures, in steel for example, bracing strategies vary from rigid connections to conventional X-bracing of each unit and external surface materials that brace adjacent units.  For tall buildings, reinforced concrete cores and complex structural connections between units and cores are designed to respond to seismic criteria.

 

A combination of the two structural archetypes can also be designed. A stack, 3 or 4 modules high (the feasible economic limit without structural reinforcement), is carried by a mega-structure. A tall building can be organized in this manner by providing a specially designed structural floor at every 4 stories as shown in the project shown below. 

TREET project's structural strategy

Prefabrication experiments - 526 - Planning process

 

Along with fragmenting design and building teams, conventional construction takes place in a linear process. Planning (design, financing, and budgets) is followed by construction document production by licensed professionals, open tendering, contracting, building, and commissioning. Tasks are sequenced and managed onsite until the finished building is handed over to its owner, who mandated a general contractor to complete the project as designed by the retained professionals. Within the process, subtrades are also contracted and made responsible for their coordination and adjustments in line with construction documents provided to them, often with little description or explanation. In opposition to this,  offsite construction proposes a process that begins the manufacturing of sub-assemblies in parallel with site work and that includes manufacturing criteria in the planning process. 

 

The overlapping of manufacturing tasks with onsite construction has been clearly established as one of prefabrication’s most notable advantages, as the shortening of a project’s timeline reduces everything from construction management costs and borrowing costs to construction waste, and the number of production days. Handover of the finished product and making it useful for the owners happens quicker than for onsite-built edifices. Project acceleration can also lead to a decreased environmental footprint, as worker-hours travelled to and from the building site are minimized. While these potential advantages are not subject to debate, the cost of ensuring they are realized is greater upfront planning. This planning should include a collaborative framework that puts manufacturers in the design phase of a project for professionals to consider manufacturing logistics and criteria. Good communication is the key with all design stakeholders to predefine and coordinate structural, architectural, and mechanical systems. 

 

Respecting manufacturing possibilities from the start also implies construction documents, drawings and specs, that outline their specificities. Transport criteria can define structural grids, along with modularity, and material supply chains can limit design choices. Material constraints, coordination responsibilities, infrastructure connections, and site versus offsite assignments must all be established upstream. This intensive upfront planning upends conventional construction methodologies, and increases design costs but can lead to efficient and cost cutting timeline compressions in the long run. Repeating this harmonized process and team-based design, while considering manufacturing, adds value to individual projects and for serial production can lead to even greater economies by spreading costs over multiple projects.

Traditional planning versus planning with Offsite construction

Prefabrication experiments - 525 - Making Sense of Modular

 

The latent economies of modular volumetric construction include bulk purchasing aligned with reliable supply chains and predictable demand, reducing waste at every step of the manufacturing process and harmonizing design with fabrication and assembly parameters. Like any other industrial product, the rationalized relationship between standardization and design variants is the baseline for increasing efficiencies and scaling economies. Variants, in architectural design, are necessary to respond to particularized client demands; this customization constrains the overall process toward specificity which has always been the model of conventional construction. 

 

Adapting manufacturing to construction's «prototype» zeitgeist requires conceptual positions that look beyond the historically acquiesced bespoke building. In a modular volumetric construction project, process efficacy is related to reducing the number of unique modules produced for a project. A greater number of individualized units increases per-unit costs, while high levels of repetition can drastically reduce per-unit costs, following the underlying logic of mass production. 

 

A project where each module is a flat, for example in student housing or hotels, modularization can attune the factory to one type of module used in one or even over multiple projects. Collective housing blocks can also include reproducible organisations and parameters where apartments are composed of one module for wet cores and other modules for adjacent spaces. Aiming to synchronize production with design variants is possible by designing modularized replication of subassemblies into projects according to their production criteria - this is basic platform theory. 

 

Minimizing variants and working with catalogued or made-to-stock modules can increase the reproduction factor. A quotient of total number of modules divided by typical modules can explain potential gains in production efficiencies. For example, a quotient of 10 in a project of 100 units indicates 10 typical modules are required to complete and deliver the building. One repeating module is used 10 times, higher numbers indicate greater potential economies - As a quotient of 100 would indicate 1 identical module for the whole building. This can further be optimized by designing the sequence of modules into the building planning to improve just-in-time delivery - this type of DfMA - Design for manufacturing and assembly approach bridges architectural design with process and delivery logistics.

the logic of modular volumetric construction

Prefabrication experiments - 524 - Modlines

 

Completed to high levels in a factory, incorporating the most refined details and according to rigorous quality control measures, modular volumetric boxes are shrink wrapped to protect them during transport and carried on flatbeds to construction sites as giant building blocks. The design-to-delivery process is meticulously planned down to the required staging areas where the convoy’s just-in-time sequence is orchestrated for the boxes to be craned and set into position. Spreader beams carried by cranes provide an augmented lifting surface to account for the width of the volumes to be set.  Faces are juxtaposed and stacked to form what are referred to as matelines (where modules meet or mate) or modlines in volumetric construction. Matelines usually refer to joints or segments where panels meet in planar building systems whereas modlines delineate the gridlines associated with volume edges.

 

Modules are typically stacked with one box’s roof constituting the drop ceiling of a flat or room while the next box's floor structure is strapped and bolted to the previously set volume forming a discrete ceiling and floor connection. A vertical sequence of two boxes in width is piled up to the roof, before going on to the next series. This vertical sequence ensures that roofing is quickly installed to protect volumes during construction as manufactured boxes are delivered without permanent weather protection. 

 

Once set in place, mechanical, electrical and other systemic connections proceed. Systems are either capped off or modularized to facilitate on-site coordination. Access hatches, traps or other facilitating devices are incorporated to be finalized on site. When exterior cladding is installed off site, perimeter edge strips are left unfinished to be weatherproofed, insulated and covered. This approach exposes the modline grid on the finished building. Another strategy is to transport incomplete boxes where weatherproofing and cladding is contracted and completed on site dissimulating modlines behind a continuous cladding to resemble a conventional build. The standalone nature of the stacked factory-made boxes comes with a certain degree of material redundancy (double structure for floor and roof compositions), however this redundancy, when detailed properly, can lead to much greater acoustic performance as compared with conventional builds where two stacked flats share a single floor composition.

Setting of factory-made volumes

Prefabrication experiments - 523 - Standards and In-factory Inspections

 

Buildings erected using factory-made subassemblies or large volumetric modular chunks must conform to the same codes and regulations that apply to conventional construction methods. Fire ratings, means of egress, dimensional criteria, and sound transmission are all defined by prescriptive construction assemblies. These provide the basis for minimal construction quality to ensure the health and safety of occupants as well as a building's stability and durability. Architects, other professionals or authorities having jurisdiction (AHJs) supervise or inspect assemblies on site to confirm conformity with building codes. 

 

The logistical nightmare associated with having to adapt factory finished elements on site argues for their upstream inspection and for any corrective measures to be applied in the factory before they are delivered to site. Industrialized building is effective when it is part of a streamlined and cost-efficient design-to-delivery process. In Canada, the CSA A-277 standard provides an outline for qualifying factories and certifying that modular volumetric sub-assemblies, prefabricated buildings or prefabricated panels meet minimum requirements before they leave the factory.

 

A277 provides requirements for  « a) certification of the factory quality program;  b) certification of the prefabricated product; c) auditing of the factory quality program; and  d) in-factory inspection of the prefabricated product.» First developed for the prefabricated housing sector as an evolution of the still applicable CSA Z240MH which states the minimal requirements for manufactured homes fabricated on a steel chassis, CSA-A277 can apply to all building types and is being used to certify factories producing modules for schools, hospitals and collective housing blocks. 

 

Third party independent inspection agents certify factories and their output.  AHJs and professionals can cooperate with manufacturers, ideally during the design stages to understand their processes and outline the required scope of stakeholder engagement to account for in-factory certifications. As is the case with many other modularized factory-made components, unitized curtain walls, mechanical equipment, kitchen cabinets, and specialized devices, conformity is established as part of a harmonized inspection process.  

 

CSA standard series Z250, Z251, Z252 (not yet referenced in Canadian codes) further regulate modular construction considering the current uptake of offsite construction to standardize elements that include transporting, setting, juxtaposing and assembling factory-produced boxes.

CSA A277 conformity sticker

Prefabrication experiments - 522 - Rebel DfMA - The «Over-the-Wall» Problem

Each major advance in manufacturing techniques spawned experiments for bringing the same efficiencies to building construction. DFMA - Design for manufacturing and assembly is a management methodology related to breaking down the barriers between designers’ visions and fabrication parameters. Cited as the «over-the-wall» problem, authors Boothroyd, Dewhurst and Knight (1983) from the industrial design field, described a framework to reduce waste as well as to streamline tasks through an optimized production process synchronizing supply chains and design with production criteria. Reducing the number of pieces and parts in an assembly is the conceptual basis for this lean industrial design strategy. 

 

Recently conceptualized for building construction, DFMA or construction-DFMA rewires conventional construction practices through maximised use of offsite manufactured sub-assemblies to facilitate the onsite erection of any type of edifice harnessing the already well documented advantages of prefabrication. Platform DFMA (another conceptual variant) offers further gains by centering the design of diverse buildings on similar components and their shared details. 

 

Rebel DFMA is an American company with a value proposition articulated to digital modelling as a fundamental part of an integrated DfMA process. Virtual modularization, high-level-of-detail modelling, streamlined shop drawing generation along with the production of onsite user-friendly assembly manuals outline the company’s services. The highly detailed models encapsulate segments, modular and coordinated parts that can be contracted to factory partners and delivered just-in-time to building sites to be put together according to precoordinated processes. DfMA brings the designers to the factory floor before design so that initial design ideas account for their manufacturability. 

 

DFMA requires advanced planning and systematization of tooling, materials, methods and supply chains making this process applicable to any building. BIM has provided an inflection point for digitization to reform construction. It has also provided a wave of interest for new prefabrication theories to emerge. Although DFMA certainly provides a lean framework, it can be argued that it has become just another catchphrase for shedding the archaic connotations associated with prefab, manufactured building or industrialized construction. 

Image from Boothroyd, Dewhurst and Knight (1983)