It appears that the residential construction market is approaching a moment where cultural, economic and technological conditions may well empower a revolution in housing production. Research conducted by the Urban Land Institute has shown that consumer demand for greener housing has been growing rapidly in recent years, and that buyers are willing to pay a premium for environmentally conscious housing. Creative financing methodologies abound in the residential lending sector, including energy efficient mortgages from Fannie Mae that apply savings in energy costs towards income requirements for prospective homebuyers. This, coupled with both a growing awareness of global warming, rising energy costs, and consumer worries about the adverse health consequences of many normative construction practices, is driving a change in the nature of consumer demand that is, at the moment, poorly understood by most builders.
KieranTimberlake
Kevin Pratt, AIA
In the current North American housing market there are few options available to buyers interested in purchasing a sustainable home. Despite unprecedented growth in the construction of new housing (figure 1) and the efforts of various government agencies to promote energy efficient housing the residential construction industry has not seen significant qualitative change since the advent of forced air mechanical cooling systems more than half a century ago. An analysis of the industry in the United States reveals that over 90% of all new homes are site built (figure 2), the great majority by small contractors and without significant architectural input. Despite recent and ongoing industry consolidation, large publicly traded homebuilding firms like Toll Brothers, Pulte and Beazer accounted for just 22% of all new homes built in 2004 [1]. One consequence of such an atomized means of production is that knowledge of sustainable practices in both construction and design must percolate widely through a diffuse and loosely integrated industry if a significant number of sustainable homes are to be constructed. Furthermore, since many new homes are designed and financed on a per unit basis the additional costs associated with sustainable construction cannot be amortized and thus must ultimately be paid by the homebuyer.
Figure 1. Number of homes completed 1992-2003 by region. Source: US Census Bureau
Figure 2. Single family homes by region & manufacturing type 2003. Source: US Census Bureau
Prefabrication offers opportunities to remedy these problems. In an off-site fabrication production model, where a manufacturer produces multiple homes using similar construction methodologies and sustainable strategies, requisite knowledge can be concentrated in a small number of people responsible for designing and building a large number of technologically similar houses. In this model wide diffusion of knowledge is not necessary to produce a large number of sustainable homes (figure 3). Prefabrication also offers other savings in both time and money that can either be passed on directly to the buyer or used to finance sustainable systems that have high initial capital costs but offer long term benefits.
Figure 3.
Unfortunately sustainable design does not currently appear to play a major role in the small but growing American prefab housing market. This is surprising, given that many of the difficulties inherent in using a sustainable approach to homebuilding are mitigated by the consequences of mass production. The rigorous environmental analysis of prototypes - which is often costly and impractical in the one-off market - is almost entirely absent, although some builders and architects use a LEED type checklist approach to green issues. The ability to amortize development costs in a "design once/build many" model should allow the incorporation of green component elements having up front R&D expenses that would exclude them from one-off projects. These elements might include adaptive systems, and energy saving technologies dependent on IT based building intelligence.
Prefabrication also helps reduce the impact of construction at the building site. Site disturbance is reduced by minimizing staging area and on-site waste generation is reduced simply because most of the construction is taking place elsewhere. Furthermore, it is much easier to control waste streams in a factory, where waste can easily be separated for recycling at the point of creation on an assembly line, than at a building site where, experience tells us, material separation is often difficult to achieve.
Prefabrication lends itself to recycling of the buildings themselves as well, since factory-built elements are more easily removed and interchanged and components can be designed with whole life cycle costs taken into account. One can imagine a trade in used house modules, which might offer an alternative to families who find their basic housing needs changing but who do not necessarily want to buy a new home. This would be a sea change in the way that consumers view houses which are generally perceived by the public as both static and complete. There have been attempts to investigate type of scalability in the earlier part of the century, although with an emphasis on easy expansion rather than easy contraction. Our cultural inability to contract when necessary, the way that natural systems do when placed under stress, often leads to poor distribution of available resources.
Another serious issue that is routinely overlooked in conventional energy budget analysis of site built construction is the enormous expenditure of fossil fuels used in transporting materials and labor to jobsites for assembly. In a comparative analysis of a prefabricated dormitory building at Yale University and a site built dormitory in Middlebury College, KieranTimberlake found a significant difference in the number of miles driven by workers involved in the two projects, with significant energy savings being realized at Yale (figure 4). Construction workers (often driving light trucks and SUVs) routinely travel upwards of 100 miles a day to remote job sites, while factory workers, having a stable and stationary place of employment, commute much shorter distances.
Figure 4.
The major problem, historically, with prefab housing lies in its inherent lack of response to local conditions. Buckminster FullerŐs round Dymaxion house, to take an iconic example, was specifically designed to be aclimatic and unoriented. Opportunities lie in the use of mass customization and IT driven manufacture to modify individual unit response to site topography and climatic variation. This does not appear to be currently available. One can imagine a mass customized prefab housing scheme where variation is driven by climatic and environmental factors in addition to consumer aesthetic and functional preferences. Some precedent exists in German factory built housing where digital manufacturing allows for a variation in exterior wall thermal characteristics. Possible fertile areas of research include developing methodologies for rapid analysis of system permutations to tune specific environmental performance variables. Mass customization also might allow the development of a process flexible enough to encompass the production of units suitable for either rural or urban environments, thus allowing access to an identified market traditionally served by on-site builders.
The current state of housing prefabrication in the United States stands in stark contrast to many other parts of the developed world. In parts of Scandinavia, more than 90% of all new housing is factory built. In central Europe, companies like GriffnerHaus are producing homes that consume a fraction of the energy used by typical American-built dwelling. In Japan, large, vertically integrated housing corporations dominate the market, with companies like Toyota having built sophisticated IT driven assembly plants (figure 5) capable of producing thousands of housing units per year. The factory built housing industries in these countries have moved well beyond simply shop building house components using site-building technologies, and have incorporated CAD/CAM manufacturing capabilities, Enterprise Resource Management strategies and software, and advanced building simulation capabilities into their manufacturing processes. Consequently, they are able to produce high quality, high performance housing at relatively low cost. Given the nature of global finance capitalism and the opportunity presented by the large, profitable, and relatively unsophisticated US housing industry, it is only a matter of time before companies from these countries attempt to leverage their technological advantage in attempt to capture a portion of the US housing market. If American companies cannot match their production capabilities, they will undoubtedly suffer. The parallels to events that took place in the automotive industry during the last quarter of the twentieth century are obvious.
Figure 5. Japanese housing production (Toyota).
Fortunately, it appears that the residential construction market is approaching a moment where cultural, economic and technological conditions may well empower a revolution in housing production. Research conducted by the Urban Land Institute has shown that consumer demand for greener housing has been growing rapidly in recent years, and that buyers are willing to pay a premium for environmentally conscious housing [2]. Creative financing methodologies abound in the residential lending sector, including energy efficient mortgages from Fannie Mae that apply savings in energy costs towards income requirements for prospective homebuyers. This, coupled with both a growing awareness of global warming, rising energy costs, and consumer worries about the adverse health consequences of many normative construction practices, is driving a change in the nature of consumer demand that is, at the moment, poorly understood by most builders.
Furthermore, there is ample evidence that the residential construction industry is approaching capacity as new housing starts pass the 2 million mark. The NAHB has estimated that the capacity of existing supply networks is approximately 1.7 million starts [3], and the expected results of over production, including local and national price instability and shortages of skilled labor are already in evidence in many local markets around the country. There are two ways of increasing industry capacity: adding production - nearly impossible given labor shortages - or improving efficiency. Given that prefabrication requires fewer workers, but provides better, more stable employment and more efficient production, it would seem to be an ideal solution to such problems. It is interesting to note that the shortage of skilled labor, coupled with an aging workforce less able to cope with the environmental variability of the jobsite, is considered to have been a major driver in the development of the prefabricated housing industry in Japan and Central Europe [3].
Finally, the technology that will enable truly industrialized production of housing has progressed rapidly during the last decade and is now becoming widely available. Although much of the technology has been developed overseas, it is beginning to penetrate the American market. Early adopters like Bensonwood Homes of Walpole New Hampshire, using hardware and software developed in Germany and Switzerland, are able to produce panelized timber frame homes using a digital fabrication methodology that employs computer controlled cutting, milling and nailing equipment. This process allows a direct translation from a three dimensional digital model to a componentized house, ready to ship and be assembled rapidly at the jobsite. If this technology is married to advanced computer simulation techniques that allow building performance to be tuned to local environmental conditions and consumer preferences, the dream of mass producing sustainable, affordable and desirable housing may finally be realized.
Endnotes
1. Public Homebuilders Council of America website, www.phbca.org June 22, 2005
2. Rose, Jonathan The Business Case for Green Building Urban Land Magazine. The Urban Land Institute, Washington, DC, June 2005.
3. Grossman, Gary Former Chair, Building Systems Council of the National Homebuilders Association, personal communication.
4. Maeda, Junchiro Automated Construction in Japan Lecture, Engineering School, University of Pennsylvania, April 11, 2005.
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