We do not build cars by dumping the parts in a driveway, so why should we build homes by dumping the parts in a yard?...
This opening statement comes after years of job site observation where it was not uncommon to see piles of construction waste and wood products such as trusses, plywood, and lumber stacked in mud and being left exposed to the elements of rain, snow, heat and cold…being abused and just overall not looking like a showplace that should be the respectable holding ground for elements required for a future home.
This question is also the basis for the following observations and why we should consider a systems approach to housing. The systems approach includes terms such as panelized, manufactured and modular, each of which fall under the definition of prefabricated.
In keeping with the affordable theme of my initial blogs, which is also the catalyst for my development of “the shelter series”, I will focus on panelized systems. In my experience these tend to be the most economical in the prefab arena. I am referring to a final construction of cost for the completed home of under $60 per square foot, and in some cases this also includes lot and development expenses.
While I understand and appreciate the merit of modular systems, I have yet to see housing developed at a cost which can compare to panelized. My findings understand most of the increased cost of modular construction is due, in large part, to additional engineering and detailing required for transport. The obvious advantage to modular is the home is pretty well move in ready when delivered to the site and placed on the foundation…and I am sure, with time, the cost obstacle will be resolved that will make modular housing a more mainstream option outside the most familiar manufactured housing models, which includes trailers.
Panelized construction systems are most typically defined as structural insulated panels (SIPs). SIPs consist of a sandwich of two layers of structural board with an insulating layer of foam in between. The most common boards can be oriented strand board (OSB), plywood, sheet metal or cement board. Insulation choices include expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam, with EPS being the most common.
Typical panel widths are from 4 to 12 inches thick with a rough cost of $4 to $8 per square foot. The R-value for EPS is roughly 4 per inch, so a panel consisting of 3.5 inches of foam with ½ inch of structural board is close to 14. Panel sizes are available from 4ft wide by 8ft high to 24ft wide by 10 ft high. The larger panels will have better thermal properties but the smaller panels may be easier to manage on site due to the weight of the material. Typical material cost for system ranges from $4 to $8 per square foot.
Door and window openings can be precut based on specified product dimensions and come ready for installation. Electrical and plumbing chases can also be precut cut into the panels although some contractors may elect to do this on site.
Other systems and techniques that could be included in this conversation are insulated concrete forms (ICFs), which is a system gaining in popularity due to cost and performance, and optimum value engineering (OVE) which was developed to result in lower material and labor costs while improving energy performance for a wood frame building. Anyone building traditionally should consider this approach. For additional information search “optimal value engineering” or refer to “ANSI National Green Building Standards”.
While there are many, many builders out there that treat the traditional construction process with a great deal of respect there is still much room for overall industry improvement. The systems approach will not only clean up the job site and reduce waste but produce a better end result. And quite often that end result is more economical, especially when considering the costs associated with waste and reduction in on site labor requirements, more timely due to shell and dry in being completed quicker, and a higher degree of quality due to the pieces being constructed in a controlled environment.
I know I am not alone in my quest for high quality economical construction systems that address the needs for responsible affordable, attainable, and relief housing in a manner that retains the dignity desired from everyone that wishes to call a house a home.
As always, there will be pros and cons to any and all systems, you need to select the one that fits as many of the concerns you have with cost, integrity, and performance as possible.
I am very interested in your responses, please share your thoughts, ideas, and observations so we all may benefit…
Posted: 3/1/2010 7:03:14 PM by
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