Prefabrication of Timber Buildings based on Digital Models: A Perspective from Norway

A few months ago, in November 2004, I had the opportunity to visit Norway to participate in a seminar and workshop organized by the Norwegian University of Science and Technology (NTNU), aimed at developing a new study and research program on the prefabrication of timber buildings based on digital models. The faculty at NTNU anticipates that in contrast to pure geometric and 2D CAD models, the product intelligence in a building information model (BIM) will enable a higher degree of industrialization and prefabrication in the construction process in Norway, and is a subject worthy of critical research. The objective of the seminar, which was held in Oslo and open to all professionals, was also to make the Norwegian building industry better aware of this technology shift that was happening in the AEC industry at large.

At the seminar, I provided a broad overview of building information modeling (BIM) and explored its potential application to the design and construction of prefabricated timber buildings. Other presenters included developers, architects, and academics from Norway, Germany, and Switzerland, as well as a representative from the US-based firm of KieranTimberlake Associates, best known for its principals' seminal book, Refabricating Architecture. This AECbytes feature article captures the highlights of the NTNU seminar from a technology perspective, and briefly explores the possible correlation between the computational technology of BIM and the constructional technology of prefabrication. But first, here is an overview of the building and construction industry in Norway for those not familiar with it.

Building and Construction in Norway

Wood has always been the most widely used building material in Norway, a natural choice considering that close to 37% of the surface area of the country is covered by forest. An example of both a traditional Norwegian structure as well as a modern-day building is shown in Figure 1. Apart from its ready availability, wood is seen in Norway to have other advantages when used as a building material: the construction is simple and gives warm, tight houses when built according to good craftsmanship; it is also a material well suited for artistic work. There is a high level of competence in the use of wood in Norway. Pine is a commonly used raw material; also popular is glued, laminated timber ("glulam"), a specially developed, lightweight and strong product that is used for homes, large public and commercial buildings, and even bridges. The main terminal building of the Oslo Gardermoen Airport (see Figure 2) is the largest laminated wood structure in the world. Norwegian manufacturers export various timber and wood products such as wood flooring and prefabricated elements, as well as other building materials such as granite, larvikite ("blue pearl"), marble, schist and several varieties of slate to the global market for construction purposes.

For more information about Norway's architectural heritage and its building and construction industries, see www.olavsrosa.no and www.nortrade.com respectively. Another useful resource is the article "Architecture in Norway" authored by the manager of the Norwegian Architecture Museum.

One of the important characteristics of wood-based construction is its suitability for prefabrication. Components can be built offsite, and are not too heavy and unwieldy to be transported and lifted into place. Prefabrication also controls construction costs by economizing on time, wages, and materials. It is particularly useful in countries like Norway because of the extreme climate. Barring a few months of the year, it is simply too cold to be building on site. Thus, there is growing interest in Prefabrication in Norway, which, along with systematic building, has also helped to extend the dominance of wood in its construction industry.

Seminar on Prefabrication and Digital Models

Since the purpose of the NTNU seminar was to investigate the still unexplored link between digital models and Prefabrication, most of the individual presentations were focused on either digital models or on Prefabrication. Three different representatives from Norway's building industry provided their individual perspectives on the state of the art of its technology adoption, particularly with respect to digital models. Gunnar Næss of Næss Architects, President of the Norwegian Association of Consulting Architects, described how his firm used ArchiCAD in advanced ways for projects ranging from interior design to congress buildings and urban planning. A case in point was the Congress Center Folkets Hus project, where a 3D model was built with ArchiCAD and all the other deliverables including 2D drawings, renderings, animations, and schedules were derived from it (see Figure 3). The firm also uses ArchiCAD's GDL scripting language to build its own libraries of parametric "intelligent" objects, particularly furniture and lights for use in its interior projects since these are not yet available from manufacturers. An advanced example of the use of GDL is Cinema Designer, an application created inhouse by Næss Architects for designing the interior of a cinema hall, in which not only are all the objects fully parametric, but the relationships between them are captured in parameters as well and can be manipulated interactively. The firm has also used ArchiCAD for a 4D project, the Hommelvik School, where the 3D model was linked with time sequencing to explore construction scheduling (see Figure 4).

The Norwegian developer's perspective was presented at the seminar by Lars Christensen of the Selvaag Group, a company engaged in several businesses and projects, one of which is construction. Its subsidiary company, Selvaagbygg, is a leading house builder in Norway that has built nearly 45,000 homes, ranging from traditional houses to apartment blocks, in and around Oslo. It is currently building 1500 new homes at Løren in Oslo, creating a totally new urban district. Selvaag Group sees technology as a critical component of its business, and has a dedicated subsidiary company, Selvaag BlueThink, which develops methods and IT-based tools for knowledge based industrialized house building. It also has Selvaag SpinOff, an incubator for the development of pioneering processes and materials supporting the group's construction activities. The company researches and uses technology in advanced ways, going way beyond CAD (2D drawings) and even beyond BIM (object-based 3D model) to a model-based specialized application for housing design: RDBH (Rule Based House Developer). This system captures housing design rules and domain knowledge to automate different aspects of design: generative rules are used to automatically create a detailed design from a conceptual model, while evaluative rules are used to check the designs for the satisfaction of specified criteria and constraints. Selvaag is also developing a digital product catalog, called Intelligent House Configurator (IHC), for use in their housing designs. The IFC is a critical component of Selvaag's technological vision to achieve quality, efficiency, and cost-effectiveness throughout the design and construction chain, and the company is very involved in the IAI interoperability effort. One of its projects, House 6 on Munkerud, is one of the four official test cases for the IFC 2x2 certification, and it brings together the use of several applications from different vendors, as shown in Figure 5.

A detailed example of the use of BIM on a Norwegian building project was provided by Kjell Ivar Bakkmoen of C. F. Møller Architects, which is working on the Akershus University Hospital project, a major hospital in the suburbs of Oslo, Norway. The old hospital is being replaced by approximately 120,000 sq. m. of new buildings, with 5,500 rooms of which 1000 are unique. The project budget is NOK 7.64 billion (approximately 1 billion USD). Construction began in March 2004, with occupancy planned for October 2008. Given the huge size and complexity of the project (see Figure 6), the main focus of the use of BIM was to keep track of all the objects—rooms, components, fixtures, furniture, and equipment—not just during design and construction but throughout the project lifecycle. To date, over 3000 drawings have been derived from the model created in ADT. IFC was again a critical component of this project, enabling the model to be used for consistency checks, quantity takeoffs, clash detection, energy analysis, fire egress and environmental hazard studies, 4D visualization, and checking the design for the satisfaction of programming requirements. Needless to say, the Akershus University Hospital project is regarded as a front runner in Norway in the use of IFC-based BIM.

A variety of perspectives on Prefabrication were also presented at the seminar. Chris MacNeal of KieranTimberlake Associates described his firm's extensive research and actual work in the areas of modularity, mass customization, and offsite construction for building components ranging from composite door panels and curtain walls to entire rooms, as in the case of an addition to a residential college at Yale University that was located on a restricted site with other construction constraints. While the firm makes extensive use of rapid prototyping in its work, it currently uses generic 3D modeling applications such as AutoCAD and Rhino for building its 3D models. While these models are useful to the designers and the clients for better visualization and also serve as input to 3D printers, the firm sees the need to eventually develop 3D models capturing real world material and property information for a more efficient and effective modular design and offsite fabrication process.

Thomas Bock of the University of Munich in Germany drew from his extensive experience with construction in Japan to describe the role of robotics in the mass production of building components and modular construction. Paul Schär described the use of digital tools in his company, Hector Egger Holzbau, which is based in Switzerland and specializes in the production of timber structures and components. It has developed its own inhouse web-based application, BauOffert, which links to its catalog of components and can be used to quickly design the structure of a timber building and produce a cost estimate. And finally, Martin H. Kessel of Technical University of Braunschweig in Germany provided a look at the state of the art of its prefabricated housing technology. He also provided an overview of Cadwork, a popular CAD/CAM system developed in Germany that was specially tailored to the demands of timber/log construction and provides an integrated solution for all stages of their design and fabrication (see Figure 7).

How BIM and Prefabrication Connect

There seems to be a natural correlation between the computational technology of BIM and the constructional technology of Prefabrication. Imagine if all the individual components that go into making standardized or modular building elements were available digitally as BIM models—supplied by their manufacturers—that represented as accurately as possible their geometry as well as their properties. Systems could then be developed that could assemble these components to create many different compositions, both digitally during design as well as physically during offsite construction. This would make it possible to have Prefabrication without the uniformity and monotony that characterized the mass customization architectural movement in the pre-computer days, and which also prevented it from taking off at that time. These specialized systems for prefabrication could be customized for different materials, different building types, different methods of construction, and so on, and could include all the associated information needed for the analysis of cost, structure, energy performance, and so on. If this technology was available and used even for partial prefabrication today, it would help to dramatically reduce the construction time of a project and make it far more efficient and cost-effective than the linear, on-site, one-off construction methods that continue to be the norm in the building industry.

How long it will take for this technology to become available is hard to predict. What is certain, however, is that we cannot even make a proper start until building component manufacturers start developing and routinely publishing digital models of all their components. Only then can intelligent design systems for prefabrication, or any other specialized construction system, be built.

Acknowledgments

My sincere thanks to Prof. Knut Einar Larsen and NTNU for inviting me to participate in the seminar, and to the companies credited here for making the images of their work available for publication in this article.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.

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