How do you know if prefabrication is right for your project? There are numerous contextual factors that can help determine when to use prefabrication and which approach to prefabrication will work best for your particular build.
The following article was written by Emanuel Jannasch, a professor of Architecture at Dalhousie University, film designer, and researcher. In this article, Professor Jannasch defines the factors that determine when to use prefabrication and explains which approaches to prefabrication will work best in different kinds of contexts.
Professor Jannasch kindly allowed us to repost this excerpt:
When and how to prefabricate are subtle questions that can’t be answered by novel hardware, more capital, or blind faith in the factory. And even solutions that have proven successful in their own time (e.g. precut houses in the interwar years, preassembled wood-frame wall panels in the seventies)– may lose their viability to broader developments in the technological landscape. This paper unravels some of the logistical factors that determine when prefabrication makes sense and when it doesn’t, and which approaches to prefabrication can succeed in what kinds of contexts.
The central concept is specific value, or value density. Primary manufacturers add value by reducing the net volume of material. A sawmill doubles the value of wood while reducing it by a factor of 3, for an increase of volume specific value by a factor of 6. House-framing doubles the value of material again, but increases the volume something like 20 times, so specific value is reduced by a factor in the order of 10. Sawmilling and other primary manufacturing processes naturally take place close to the resource, to minimize transport costs. Construction tends to take place closer to the site, again, to reduce transport costs. Building components and sub-assemblies can also be understood in terms of specific value. Vinyl windows, for example are of a middling value density and are assembled locally out of higher specific value extrusions and hardware that can be shipped from afar.
A survey of freight calculations shows that volume is the dominant factor in transport but that it’s far from exclusive. Weight plays a role, but smaller than may be anticipated; various kinds of fragility and climate sensitivities are actually more important. Prepping and handling are also significant. Understanding these factors helps explains why prefabrication is more successful in some aspects of building than others, and why success depends on geographic factors. The differing importance of capital in securing marginal advantage in a given process is also important. Accordingly, some industrial processes are vulnerable to lower-capital competition, others are more secure. Finally, we need to look at some hidden costs of the factory, and some unexpected economic advantages to the decentralized system of mobile piecework-subcontractors that have proven so remarkably resilient over the past century and more.
Overall we discover that each conceivable building component, preformed, pre-assembled or otherwise, has its own context-dependent radius of viability. Centralizing their separate manufactures in a comprehensive plant may simply mean that many components end up getting shipped farther than their value density warrants, or not far enough to give their production machinery a viable market.
However, understanding the principles and evolution of logistics will help us envision new ways of systematizing buildings and components. Some of these are in evidence today, some are yet to be realized. Together they suggest new kinds of construction economy. They also support a more elegant integration of systems, and a better orchestration of visual elements, intervals, and proportions.
Professor Jannasch highlights many crucial logistical aspects of building and offers a progressive analysis on the advantages of a decentralized system and the need to conceptualize new ways of regulating buildings and components.
To view this abstract on the Association of Collegiate Schools of Architecture website or to access other abstracts written by industry professionals please visit http://www.acsa-arch.org/docs/conferences-files/2012-fall-abstractbook.pdf?sfvrsn=12