Think Pre-Fab, Part 2

May 04, 2016

Austrian architect Hermann Kaufmann realized the importance of keeping construction as tight and perfect as possible because he is mainly working with wood construction. The biggest enemy for wood construction is not fire, but water. So, what’s the best way to make the joints and connections as perfect and accurate as possible? Prefabricating the main components in factories appears to be the answer. Also, careful planning and design focused on prefabrication in early design phases could result in simpler and clearer construction details, as well as significantly reduced construction time.

They started to explore prefabricated wood design in 1997 for a three-story housing project at Olzbundt. It contains prefabricated bathroom units and walls with preinstalled windows and cladding. The floors and roof are prefabricated wood hollow boxes. This same model was improved and perfected over several other multi-family housing projects. The construction details are simpler, the prefabricated elements are fewer so that the contractors are more comfortable with the concept and build them in an efficient way.[1]

Prefabricated Modular Systems

Nowadays, CLT makes prefabricated wood construction even simpler and more straightforward. By moving away from framing systems, there are fewer elements going together for walls and floors. Especially for project types such as multi-housing, hotels and dormitories, the repetitiveness of the modules is a big advantage of thinking prefabrication and utilizing CLT.

We visited and stayed at Hotel Ammerwald in a valley of the Alps. It is a prefabricated modular hotel built with CLT floors, walls, and roof. Before our trip, I was curious whether it might be a little too much wood in a small suffocated unit; I also wondered whether there would be any compromise of convenience due to the novelty of an exposed CLT interior. When we finally saw the crisp exterior facade, felt the splash of warmness in the hotel rooms, and observed the careful design of every single detail in the building, I was convinced. Most importantly, I believe the sharpness of the finished product would be much harder to achieve if it was built on site wall by wall, unit by unit. Not to mention the fact that the 96 units only took 31 days to construct at the factory—three to four module units could be lifted and secured on site only in an hour.[2]

Prefabricated Open Systems

When it comes to building types that require more flexibility and open spaces, prefabricated elements may not come to mind. There is less repetition, so focusing early planning on prefabrication may not seem worthwhile. If there is nothing but conventional construction on a project, there won’t be enough drive to go pre-fab. But among the heavy timber projects we visited during this trip, many of them are innovative in developing some sort of composite elements, and in many cases these specially designed elements are prefabricated at the factory to assure correct and integrated construction. For example, the LVL and glulam combined hollow box floor decks at Salzburg University of Applied Sciences Kuchl Campus are fire-tested as an integrated element, then prefabricated at the factory and installed on site as single spans. Even though the rest of this building is all built on site, prefabrication does allow innovation and integrity of the floor decks.

To take this kind of innovation to a higher and more comprehensive level, Creative Resource and Energy Efficiency (CREE) developed the Life Cycle Tower (LCT) system, a prefabricated open system that allows wood buildings to reach 20 – 30 stories tall. Hermann Kaufmann collaborated on designing the first two showcases with this system, LCT One and Illwerke Zentrum Montafon (IZM). Both cases adopt concrete/wood hybrid structure to maximize each material’s structural efficiency. The floor decks, highly thermally insulated facades, columns, and ceilings are all designed as modules and prefabricated at the factory. CREE’s idea is to develop different building prototypes with local architects and engineers, utilizing local materials to fit in various contexts around the globe.

LCT takes a big step forward for prefabricated commercial buildings based on heavy timber. It also reminds us that prefabricated buildings won’t reduce architects’ roles or limit our imagination. It actually encourages us to challenge the conventions, to innovate and imagine what works best. Design towards prefabrication requires more efforts to plan ahead, to collaborate closer with the manufacturers and builders across sub-divisions. Building technology and design tools have evolved a lot over the past few years, but the way we actually design and build hasn’t changed nearly as much as it should. Admittedly there are bad examples of prefabricated buildings, their fast-pacing and static nature have received lots of criticism. But I believe good examples are emerging, and prefabrication should be the future of how we design and build.

Yang Liu