From the Design Quarterly: Embracing modular and prefab for future-ready design
April 10, 2019
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Complex projects when time and space are tight are a perfect fit for off-site prefabrication and modular construction
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How much of a building can we build offsite? How granular can modularity be? In today’s fast-paced construction market, modular construction offers versatility and advantages that have designers thinking bigger, and smaller, about the possibilities for incorporating prefab components. We’re confident that modular and prefabrication methods will continue to bloom in coming years. Modularity has a lot of advantages, but with a few caveats.
Modular building is expected to rise 6% globally by 2022, with countries like Sweden (where 84% of detached homes use pre-fab timber) and Japan leading the way. A January 2017 report from the Modular Building Institute (MDI) predicts that modular construction which currently accounts for 3% of all new commercial construction in North America will grow to over 5% over the next five years. In North America, the commercial sector leads adoption of modular methods with industrial, healthcare, and education sectors following behind.
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The Cancer Centre at Guy’s Hospital in London features a frame made up of 3,756 off-site manufactured concrete elements. (Rogers Stirk Harbour + Partners/Stantec)
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Three modular approaches
Cancer Centre at Guy’s Hospital: Building on an active urban healthcare campus can be tricky. On the Guy’s Cancer Center project, prefabrication was a must. The compact project site, and hard-to-reach setting in Central London, dictated that 60% of the project was prefabricated off-site. Stantec led clinical planning and interior design at the Cancer Center for Guy’s Hospital in London with design partner Rogers Stirk Harbour + Partners (RSH+P). Our contractor partner, Laing O’Rourke saw the opportunity to use the Cancer Center as a demonstration project to show its ability to manufacture custom prefab components in its in-house “Explore” facility. The key aspect of the Guy’s modular approach was a prefabricated internal partition called a “smart wall.” The smart wall is assembled off-site with fire and acoustic performance features, electrics, plumbing, and openings preinstalled.
Our team worked closely Laing O’Rourke during design to develop digital models that facilitated Design for Manufacture and Assembly (DfMA) of the smart walls, reinforced concrete lattice slabs, columns, and interior fit-out packages with integrated service conduits. The external façade was comprised of unitized curtain walling, built offsite and craned into place. RSH+P designed extended balconies for the “villages” in the Cancer Center and these were prefabricated. The mechanicals were prefabricated. The servicing modules were manufactured offsite and brought in and interconnected. With a prefabricated lattice slab, the lower section of slab and rebar was precast before being lowered on the site, with the rest poured on site. This avoided any temporary structure. As every floor slab went up, they craned in the smart walls, constructed offsite and precision-cut with robotic arms enabling tight design quality control and significant savings in construction time.
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Yale Science Building: Science research changes at a rapid clip and today’s science buildings must be built for flexibility and expansion. As designers, we strive for methods that deliver spaces and corresponding infrastructure that meets our clients’ current and future needs, are easy to maintain, and easily modified as research needs change. Because they’re so complex, laboratories provide a perfect opportunity to explore modular and prefabricated construction technologies.
Yale University’s new Science Building (which Stantec designed in association with Pelli Clarke Pelli) is a good example of modular approaches employed for future-ready design thinking. The majority of the building’s labs are open flexible biology labs, which are ideal candidates for repetitive modular design.
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Yale Science Building in New Haven, Connecticut, where prefabrication was used for mechanical and plumbing on the lab floors. (Stantec/Pelli Clarke Pelli)
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For Yale, we embraced multi-trade prefabrication rack modules for the mechanical and plumbing corridor mains on the lab floors. This approach provides a modular structural frame in which the mechanical, plumbing, telecommunications, and other laboratory components are installed offsite. The completed assembly is delivered to the site and installed as a unit. This approach allowed the delivery of a high-level of organization and consistency in the main laboratory services, including valve locations and future piped system expansion. This consistent, repetitive approach helps the building services to remain relevant as research needs evolve.
The main vertical steam and chilled water building risers also used prefabrication. The 90-foot assemblies were constructed off-site and craned into the building as single structural elements. Modular thinking at Yale resulted in a more direct path to project completion, increased project quality control, and a significant boost to construction safety―a win-win-win for client, contractor, and designers.
Centre For Addiction and Mental Health (CAMH): At the Centre for Addiction and Mental Health Phase 1C project, a pair of hospital buildings located in Toronto’s urban core, prefabricated elements are a significant aspect of construction. Roughly 60% of the total building envelope (the exterior building envelope whole-wall panel construction for all the non-curtainwall cladding) is prefabricated.
On this alternative finance procurement (P3) project it was sensible to prefabricate certain elements offsite, such as the building’s rainscreen wall. This includes the walls for approximately 225 mental health patient bedrooms, each outfitted with a super-size window, operable vent, a complicated window with an interior sash for security, and integrated roller blinds.
The panels are generally hoisted onto the open concrete floor slabs at the exterior edge and then tilted up in place from the inside. They build the modules, bring them in, tilt them up into place, secure them, and move on. Essentially, the on-site crew can put the entire back-up wall up in one go.
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Centre for Addiction and Mental Health in Toronto, Ontario, where roughly 60% of the total building envelope is prefabricated.
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When is modular a good call?
When repetition is necessary: Modularity is a great match for repetition, where it can achieve efficiencies in manufacturing. Therefore, in the education, residential, and healthcare sectors where room types repeat, modularity has benefits. Today, it’s not unusual for prefabricated hospital bathrooms to be built by trade workers at an off-site facility and trucked to the construction location for installation. And at CAMH Phase 1C, hundreds of patient room walls are being replicated.
When controlling finishing details: A modular/prefabrication process makes it more likely that critical details (say the placement of service connections for a laboratory) can be executed to exacting standards in the workshop.
At Yale, the design control allowed us to deliver precision repetition. We were able to control features within inches in the lab modules and system, but also above the ceilings. That uniformity provides Yale maintenance personnel with consistent valving and shut off locations, providing ease of maintenance while enhancing goals for flexibility and future-proofing.
Guy’s in London features a great deal of exposed concrete, which is unusual in hospitals. Through modularity, we were able to achieve a much higher quality finish on the concrete surfaces to meet Guy’s infection control standards.
On tight urban sites: At CAMH Phase 1C there are very tight constraints with the rest of the urban hospital campus, which remains active during construction, and only a modest staging area available for construction. Prefabricating the wall panels means fewer hands on-site and less staging space needed. Similarly, at Guy’s Hospital Cancer Center in London, the tower was an expansion of an existing medical center in a dense and sensitive area on a cramped triangular site. The building was heavily scrutinized. Modular construction was 30% faster in terms of hours on-site, less noisy and therefore less disruptive to the neighbors and the functioning hospital itself.
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The Cancer Centre at Guy’s Hospital, where modular construction with 30% faster than traditional construction in terms of hours on-site. (Rogers Stirk Harbour + Partners/Stantec)
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What approaches can help us get the most out of modular?
See it as a process: At Yale, an interdisciplinary team analyzed the project for opportunities to apply prefab and tweaked the design. This design thinking led us to establish a layout of eight repeating lab modules per floor, each with a repeating single trade prefabrication that brought together mechanical/electrical/plumbing systems with future capacity and routing built into the design, an excellent fit for shop-based fabrication.
Understand that it requires intense coordination: Achieving the benefits of modularity requires early and intense collaboration. And that collaboration extends beyond the design team to the contractor and sub-trades. This collaborative and interdisciplinary approach to problem solving uncovers possibilities for prefabrication that aren’t initially obvious. Early consultation with our mechanical contractor allowed us to prefabricate the main building chilled water and steam risers, as well as the main duct risers—a surprise to the design team given the size of these elements.
Digital model to fabrication: With Guy’s, it was to our advantage to develop the clinical and architecture database and develop finished details on rooms and equipment in a 3D model environment. The engineers modeled everything in BIM. The 3D modeling tool is a crucial communication tool—presenting our project design to the Guy’s client group, including patients, so that they could understand fully the design intent. It was crucial that we delivered in a digital model because that model, once translated, became the blueprint for fabrication.
Where is modular going? Currently, there are limitations to the application of modular building. Two of the floors at Yale Science Building, for example, were too specialized to reap the benefits of multi-trade prefabrication, although single-trade prefab was leveraged. At Guy’s, erecting smart walls as the building was going up created an unusual, albeit temporary, situation: exposed interior walls during construction. But, keeping the above in mind and challenging ourselves and clients to use their imagination, means that prefabrication and modular construction is one wave of the future that’s already arrived.
" }At Yale, the design control allowed us to deliver precision repetition. That uniformity provides Yale with ease of maintenance while enhancing goals for flexibility and future-proofing.
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Benefits of modular
Speed: Prefabrication increases speed of construction by simultaneous construction of project elements that typically follow a linear schedule. At Yale, the riser components, which would have taken a crew 7 weeks to construct on-site, were installed in 2 days through prefabrication―that’s a savings of 960 person hours on-site. At Guy’s in London, Laing O’Rourke estimates that a modular approach allowed the project to be built 30% quicker than conventional building methods.
Safety: Prefabrication takes place in a controlled environment where the benefits of temperature control, ergonomics, and standard safety protocols are present―aspects much harder to control on-site. Manufacturing, cutting, welding, even lifting can be done with the latest machinery, even robots, and OSHA (the Occupational Safety and Health Administration in the US) engineering safety controls can be put in place. And that means a more consistent product, with much lower potential for harm to workers.
Sustainability: With prefabricated components, there’s far less waste produced. In a shop environment, the cuttings from making smart walls for Guy’s, for example, can be reused or properly recycled whereas on-site, those cuttings are typically sent to landfill. This means that projects like Guy’s can pick up points toward BREEAM certification.
Quality: Modular design approaches and the idea of architectural achievement are not always thought of synonymously―but perceptions are shifting thanks to projects like Guy’s and Yale. The regularity of the laboratory systems at Yale, the quality of the finishes at Guy’s Cancer Center have a lot to say about what can be designed and achieved using modularity. One look at these finished buildings and you can see the design quality that results from prefabrication.
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