Prefabrication experiments - 377 - State of the Art - 07 - Delicate Adaptive Reuse

Neglected stone dwellings, barns, and other derelict buildings have always been objects of romanticized architectural adaptations; the dream of transforming a ruin into a house for next to nothing and reviving it for a new era or use is of particular interest in an age of resource conservation.  In degrading old towns and regions, structures can be purchased for cheap by assuming the responsibility of rehabilitating the buildings, to breathe new life into demographically challenged communities. Renewing an old house requires the delicate touch of knowing what to get rid of and what to preserve that harnesses the spirit of place embedded in weathered stones. Prefabrication and industrialized building have little to do with vernacular building techniques, however, the creative interaction between old and new sometimes elevates both, providing an image of how classic building systems and modern methods of construction can complement one another in unique adaptive reuse strategies.

 

Nauman Architektur practise epitomized this idea by transforming an 18th century pigsty into a refined 21^stcentury showroom. Extensively damaged in the second world war, the building’s existing aged materials and shapes are framed beautifully by a precise timber panel system composed as a prefabricated prosthesis inserted into the existing stone structure. The planar timber structure is arranged as a type of autonomous volume, pre-assembled, lifted and slid into place. The internal form duplicates the arbitrary patterns of existing openings and serves as a background for stone bearing walls that clearly express their tectonic link to place. The plywood insert is capped off with a slick pitched roof detail amplifying the material dualities of old and new, thick and thin, light and heavy, craft and industrial production, stacked and surfaced, evident from every point of view. The prefabricated sleeve envelopes a flexible space that could be used as a multi-use living space. Turning a low road accessory farm building into an inhabitable modern space showcases the adaptability of architecture not only from a theoretical perspective but as a hands-on way of conserving and reviving history. Prefabrication in this case speaks to its potential for sensitive intervention reducing site disturbance to a minimum. 

Exploded axonometric and volume being inserted, project by Naumann Architektur

Prefabrication experiments - 376 - State of the Art - 06 - Add-on Componentization

 

Componentization is a direct consequence of industrialization. Parts, pieces, anchors, or assemblies are mass produced and include innumerable catalogued variations to create bespoke buildings. Modern buildings are all, in a way, kits composed of these manufactured parts. Design for Assembly was one of modernism's canons that conceptually defined component prefabrication’s applications. Assembling edifices from coordinated parts inspired dimensional coordination but parts remained disparate: interfaces and systemic coordination were rarely considered in parts production. Instead, romanticized harmonious detailing of diversely manufactured parts in building construction guided the architect's role in providing instructions for coherent integration. Applying Lean production principles, BIM modeling and even DfMA principles to component manufacturing is currently reforming the sometimes disjointed and entangled relationship between design, fabrication and construction.  

 

Componentization can be further enhanced by modularization, creating coherent dimensional, joining and production parameters, to produce elements designed to fit into or added-on to buildings. Premade bathroom pods, elevator frames, staircases, precast wall panels and manufactured balconies are all large sub-assemblies becoming common as offsite production is understood as an efficient and productive alternative to archaic and wasteful onsite construction.  Sapphire, a company based in the suburbs of London, produces balconies as a type of coordinated chunk devised to simply slide onto a building's structural system. The prefabricated balcony is an assembly of two main parts; the prism (deck and rails) is conceived with two framed openings that glide the floor onto extending brackets cantilevered from the building structure like the two extending forks of a forklift. These outstretched members can be bolted to steel beams or cast in concrete slabs. The two contact points reduce thermal bridging associated with continuous balcony slabs. The module is flatpacked, delivered on site and craned to be set at a specified height.  The floor «cassette» is lightweight and includes material choices for glass guardrails and decking. The company takes modern technology even further with their configurator «coach», an on-line tool deployed to customize designs from predetermined rules and dimensions. Details can then be downloaded and specified. This type of online catalogued part and process streamlines the relationship between design and fabrication through a type of preprogrammed personalization.

Sapphire balcony being lifted into place

Prefabrication experiments – 375 – State of the Art – 05 – MTP_Multi-trade Prefabrication

 

As buildings became more complex throughout the twentieth century, integrating an assortment of services, systemic entanglement came to characterize the construction industry's fragmentation. Piping, wiring, air distribution and conditioning designated a patchwork of trades competing for space, paths, and channels for distribution. Trade coordination, or lack of thereof, is at the heart of scheduling and cost overruns in building construction. Prefabrication and industrialized construction promised to reform construction by defining and manufacturing building systems streamlined for onsite assembly. Most systems have limited their scope to structure, as is the case with partial panelized and modular volumetric construction, mechanical coordination remains a challenge in harmonizing multiple stakeholders to produce a coherent network of services. 

 

Combining the advantages of prefabrication, primarily a controlled work environment, concurrent onsite and offsite progress, with the one-off architectural designs, Multi-Trade prefabrication mandates trades to collaborate, in a factory, to assemble chunks or parts of a building that will subsequently be delivered and completed on site. The multi-trade component is an co-creative/constructive process outlined by contractual documents that identify methods, materials, place of production, tools and responsibilities for each trade brought together to construct optimized sub-assemblies. This process rationalization increases efficiencies, reduces waste, and most notably has the potential to eliminate costly coordination errors. The idea has been deployed on complex projects by industry leaders like Skanska and has even inspired a segment of production: Multi-Trade Rack Prefabrication is specifically linked to mechanical distribution chunks that are fabricated offsite in modular formats to facilitate both design and construction. 

 

BIM (building information modeling) is the main driver and facilitator for this type of prefabrication. Digital twins provide fundamental documentation and information sharing tools to organize spatial and functional criteria, specify, design, and identify coherent routes for trade interaction. Virtually designing and assembling mechanical systems before they are built makes it possible to apply both rigorous organizing principles and a high level of standardization by modularizing mechanical racks. The success of MTP hinges on an integrated process and contractual clarity imposing a comprehensive overhaul of traditional procurement methods.

Base4 Modular prefabricated MEP racks

Prefabrication experiments - 374 - State-of-the-Art - 04 - Collins House kit-of-parts assembly

 

Skyscrapers are contemporary marvels of engineering symbolizing wealth and power, just as gothic cathedrals or tower-houses were in middle-age cities and towns.  Industrialization of steel and reinforced concrete along with advances in structural computations inspired verticality to showcase modernity.  Building tall frames requires imaginative ways of buttressing these thin cantilevered beams sprouting from the ground, reaching for the sky, and anchored by increasingly small floor plates. Stacked small floor areas also require novel building methods in dense urban environments constraining traditional construction methods. 

 

Bates Smart Architects, 4D Workshop structural engineers and Hickory, general contractor, designed and erected the Collins House in Melbourne Australia in 2002 based on an innovative interpretation of an age-old idea – the box beam: a hollowed out structural section braced by its perimeter surfaces. With a height to width ratio of 16:1, the 58-floor building's structural strategy employs 4 shear walls:  2 lateral walls and 2 cross walls that form an overall H-shape braced in both directions. The service core portion of the H shape includes large vertical openings for an egress scissor stair and three elevators. The building's first 14 storeys are outlined by urban property lines, while floors above the 14th gain a 4,5 m cantilever on purchased aerial rights over an adjacent heritage building. This 44-floor cantilevered appendage is post-tensioned to its supporting lateral shear wall. 

 

The building is a manifest of current offsite construction methods applied to unique one-off edifices. Shear walls, exit stairs, cantilevered volumetric sub-assemblies were all produced offsite, delivered, set, and stitched on site.  Precast sections of post tensioned bearing walls were stacked along with complete floor sections; elements were then joined with structural mortar connections. A notable example of multi-trade prefabrication, systems are fully factory coordinated by multiple trades working together as they would onsite, but in a factory setting. Hickory group distributed contractual roles and responsibilities among trades and manufacturers. The unitized curtain walls, and temporary floor jack-posts were also installed in the factory reducing onsite work to a minimum. Modularization is applied to all building subsystems making this tall structure a giant Meccano kit-of-parts designed for precise assembly in a tightly woven urban context.  

Elevation and structural strategy

Prefabrication experiments - 373 - State of the Art - 03 - From the mobile home to the CrossMod®

 

According to the U.S.A.-based Manufactured Housing Institute's Industry Overview for 2021, the average construction cost of a manufactured home is 57$ per square foot compared to 119$ per square foot for an onsite built home - 50% less. This affordability is evidence of the successful application of industrial principles developed throughout the 20th century. From the earliest trailer coaches in the 1920s, to single and double-wide’s evolution in the aftermath of World War II, mobile homes influenced single family home production in the United States; even referred to as American vernacular by modern architect Paul Rudolf. Negative undertones associated with subpar construction forced United States Congress to adopt the National Manufactured Housing Construction and Safety Act in 1974. This increased and imposed national standards for quality to stabilize the industry's credibility. The term manufactured home also conveyed manufacturing potentials and dissociated the industry from the entrenched idea of impermanence.

 

Still representing 9% of all single-family housing starts, the dream of the industrialized house is alive and supported by dynamic forward-thinking producers envisioning greater demand coming from the current lack of housing supply and a dearth of traditional construction trades. Redefining the industry and promoting design and efficiency also led to a new term: CrossMod®. An industry initiative in 2016 highlighted the renewed need to elevate industry standards and more importantly to reach a new generation of consumers still inhibited by enduring connotations of less than par products. Linked to the crossover that has become an immensely popular breeding of cars with SUVs in the automobile industry, the CrossMod® presents some of the features of a site-built home, most notably a permanent foundation. Modular sections can also be combined and stacked to construct homes that are difficult to distinguish from their site-built counterparts and that come with the advantages of constantly improving manufacturing processes. 

 

Short some 5.4 million single family dwellings according to recent studies (USA), the market potential is clear. It remains to be seen if this most recent change in terminology will reform the industry and increase market share: 9% of all new housing starts represents a figure that is strangely unchanged from the 9% of housing starts in 1954.

Evolution from the Mobile home to the CrossMod®

 

Prefabrication experiments - 372 - State of the Art - 02 - Cross Laminated Timber's Disruptive Potential

Once pioneered, some materials revolutionize construction and architectural production. Both Steel and reinforced concrete highlighted by industrialization became the two materials most associated with modernity. Steel was touted as strong, durable and easy to put together, while reinforced concrete provided fire-proofed edifices for densely populated cities. Modernity in architecture relegated timber to small scale building embodied by  stick platform framing. Glue laminated timber, an equally modern material, made it possible to attain large spans and was largely used but has only recently been as disruptive as steel and concrete; Current climate change imperatives and regulating carbon footprint are driving its developments and use in building structures. 

 

Cross laminated timber in particular, a variant of glue laminated timber, a type of «hyper plywood» of compressed, layered, weaved and bonded pieces is offering an alternative to concrete construction. Its weight can be a third that of reinforced concrete. The CLT panels are produced as made to stock sheets, or engineered to order pieces that are cut in the factory to include openings for windows, doors, ducts or any other required openings. Once the pieces are numerically cut (2-3mm precision), they are loaded in sequence and delivered to sites. They are assembled much-like a bolted precast concrete panel system would be. Dry joinery also makes these systems as easy to dismantle as they are to assemble. 

 

A warehouse built in British Columbia, Canada in 2020, designed by Studio 531 Architects displays how straightforward this formidable building material is to work with. Once the slab on grade was cast and cured, vertical 25-foot panels were lifted to form the structure’s perimeter. The bearing wall panels function like tilt-up concrete panel systems and were considered a viable eco-friendly alternative by constructor Citta Group. The 5 ply panels were simply bolted together with cross glulam beams to carry conventional roof trusses in an efficient wall / post and beam / truss building system. Supplied by now defunct Katerra, the building took only two weeks to erect.  Saving time along with sequestering Carbon are the main advantages of this efficient building material that is rapidly gaining ground on conventional building systems.

Interior view of the simple to assemble timber kit (panels, post and beam, trusses)

Prefabrication experiments - 371 - State of the Art - 01 - Construction 4.0 and tall modular

 

A state-of-the-art study on offsite construction, including prefabrication, industrialized building systems or modularity reveals a notable uptake in interest and in use throughout the last decades. Promoted as a productive way forward in construction, novel factory or manufacturing methods are being driven by information technology and reforming a fragmented building industry into a data centric cooperative community of stakeholders. BIM (building information modelling) is at the core of this transition. Data sets are incorporated into a virtual model earlier in the design process potentially streamlining design with manufacturing.

 

Digital design, modelling, fabrication, and monitoring geared to the making of buildings has been referred to as construction 4.0. This fourth industrial revolution is disrupting conventional construction and promises to create more efficient buildings. As Ford and Toyota radically altered the way things were made, DfMA principles along with new manufacturing technologies will become mainstream within the construction industry; robotics, additive manufacturing, generative design, and artificial intelligence are developing a space for new materials, systems and processes to replace conventional means. 

 

Even with all the potential for newness, modular volumetric and panelized construction remain go-to systems. Both have existed within the offsite space for decades and panelized has transformed light wood framing due to the rarity of traditional trades. Modular volumetric is promoted as the most modern of these methods, due to its speed of erection. Stacking factory made boxes certainly epitomizes Offsite construction as in principle only infrastructure and mechanical connections are completed on site. Currently, tall modular is providing a window into how industrialized construction can be deployed to increase productivity. Built from 2018 - 2020 in London by owner, developer, builder, Tide construction, 100 George Street is a notable example of combining the potential speed, precision, and quality of volumetric modular. Two 38 and 40 story towers are made up of 1500 boxes produced by manufacturer Vision Modular Structures. The use of digital modelling tools to organize and harmonize different stakeholders reflects current practices. The owner, developer, builder collaborative model exposes an integrated design-build approach that makes it possible to involve manufacturers in the planning phase. Including offsite criteria in planning is essential to fulfilling the touted advantages of offsite construction.

100 George Street by Tide Construction

Prefabrication experiments - 370 - Modern structural archetypes - 10 - Waffle slabs: monolithic space frames

Industrialization stimulated a generative relationship between structure and architecture. Ideas federated from both disciplines forged rational and robust buildings through the rigorous repetition of components and assemblies. Networks of linear lightweight members, monolithic waffle slabs and ribbed shells symbolize this union’s aim for maximum architectural space with minimal material use.

 

All manner of reproducible elements were knitted into rigid textile-like curved or planar surfaces «packing space» as Buckminster Fuller would articulate using his tetrahedral truss. Triangulation, truss effect and materialized lines of stress symbiotically increased structural inertia and stability. These modular grids and networks argued in favour of prefabrication in skeletal frameworks, in timber or steel, as well as in lamella vaults and filigree domes. Ribbed surfaces allowed similar optimizations in monolithic concrete structures, exposing a lattice of beams, girts and sustaining segments. In medieval ribbed vaults, compressive lines of stress materialized load transmission. These spines can be formed with equivalent or varying depths to further express load transmission. A beautiful play on structural rhythm, the waffle slab used by Louis Kahn in the Yale Art Gallery in New Haven, Connecticut or John Lautner’s modern masterpiece, Sheats–Goldstein Residence, came to characterize modernism with its rhythmic sequence and gothic imagery. Cast in orthogonal, triangular grids or even more dynamically by Pier Luigi Nervi, all were deployed to reduce reinforced concrete’s prohibitive dead load (2400 kg/m3). 

 

The simplest systems place and align dimensionally uniform prefabricated boxes over flat formwork to define a pattern of voids into which rebar is positioned and concrete poured, hardened and cured - the resulting waffle effect and criss-cross pattern buttresses a relatively thinner horizontal slab over the formed ribs. The formwork could be reused or left as part of the structure’s geometry if made of some type of thin shell material. The voids from waffle forms could be used for architectural lighting to amplify the systemic patterns.

 

Today, digital technology allows for this type of structural rationalization to develop ideal patterns and link this data to code machines to create specific formwork components to further optimize ribbing or arching patterns.

Left: Yale Art Gallery; right: Sheats-Goldstein residence

Prefabrication experiments - 369 - Modern Structural Archetypes - 09 - Panelized Frames

The relevance of factory production in architecture and construction has often been expounded by crises. The enormous material and human devastation of World War 2 combined with accumulated housing shortages in Europe underwrote massive housing production and its normalization. In North America, returning soldiers and the baby boom also pressured housing supply; both continents needed to build more and quicker. Standardization became key to two evolving building systems that in a sense represented their contexts’ political and social progression. Balloon and platform light timber frame construction complemented by onsite rigorous sequencing became the go to system for single family dwellings whereas standardization elevated the use of concrete panel systems for collective flats in Europe. The large panel building was democratized using a very simple structural system: the wall and slab monolithic hive archetype combines surface elements to create inhabitable cells in plan, section, and elevation. Bearing walls and spanning floor surface elements arrange simple one floor unidirectional tube-like apartments on either side of a central corridor.

 

The planar bearing elements and spanning slabs are connected through monolithic joinery. Extending reinforcing steel bars are tied together and specially formulated high strength low-shrink mortar fills the gaps bonding vertical and horizontal elements.  The panels were sometimes cast in place or in a factory but usually on some type of horizontal casting surface or vibrating table. Flat-packed and transportable, the reinforced concrete panelized structures are monolithic, inherently fire-proof and robustly stable with vertical and horizontal panels contributing to lateral resistance. Panels for exterior walls could be faced with ceramic, brick, or any other material, but it's the structural simplicity that made the system successful in so many different contexts. The panel and slab system including standardized planning principles could be deployed and improved from building to building, deploying replicable details and processes. The wall and floor frames have recently been examined once again in relation to affordable housing stock only this time highlighting mass timber potentials. CLT panel and slab buildings use similar configurations to concrete large panel typologies with the added advantage of carbon sequestration.

Large precast reinforced concrete panels and prototype building in USSR

Prefabrication experiments - 368 - Modern structural archetypes - 08 - Moment frames and connections

 

In skeletal construction, post and beam, box, balloon, platform or regular braced frames, joints and connections between vertical bearing elements (columns/posts) and horizontal spanning elements (beams / girders) are either nailed, screwed, bolted or riveted. These pin connections resist vertical gravitational loads and transfer constraints from one element to another taking the path of least resistance. Generally flexible, these joints are located where moment and shear forces are at their summum. Flexible frame connections require some form of bracing, diaphragm planes, or diagonals to lock connections in position to resist lateral loads. Moment Frames are skeletal constructions where conventional flexible fixations are replaced with more complex rigid or moment connections to keep the frames stable. 

 

Portal moment frames like the infamous Butler steel building frames, invented in 1940 by Wilbur and Kenneth Larkin of the Butler Manufacturing Co., express compression constraints by tapering elements to mid span where bending moment is at its minimum and enlarging elements at points of maximum stress. The connections are rigid; instead of standard bolted beam to column joinery, the constituent parts are either welded together or bolted with larger stiffening plates. The connection is further reinforced by welding plates in webs to ensure a complete transfer of bending moment and shear stresses from the horizontal to the vertical. Deformation or displacement of the moment connection implies bending or distortion of the entire frame which makes the whole system behave with monolithic geometry. Tapering composing parts reduces material use but connection complexity makes this frame's use appropriate only where completely open spans are required, arenas, factories, etc. 

 

A beautiful example of a moment frame designed by Camenzind Evolution in 1998, the Sports centre in the city of Uster in Switzerland employs hinged rigid frames to reduce effective spans and present an elegant structural solution derived from structural analysis; wide flange beam are shaped according to stresses. In these types of portal frame structures, rigid joints resist lateral constraints in their traverse direction while roof surfaces play a structural role bracing frames in their longitudinal direction.

Butler Frame (left), Sports centre frame by Camenzind Evolution (right)