This article was originally published in the March/April 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online March/April 1999

in energy

Prefab Utility Walls Save Up-Front Costs

The ResCore's double stud, layered construction enables fabrication of plumbing and electrical systems prior to assembly. 
The largest ResCore prototype built included three adjacent and interconnected utility walls. These serviced 1 1/2 baths, the kitchen, and a laundry/utility room.
Off-loading a two-wall ResCore system in Plains, Georgia, was accomplished by six Habitat for Humanity volunteers.
This completely installed two-wall ResCore system awaits the construction of the remainder of the house. Under normal field conditions, off-loading, placement, and connection to below-floor utilities would take less than two hours. 
A new product called the Residential Utility Core Wall (ResCore) can save from $500 to more than $2,000 in construction costs for site-built homes. The savings are in materials--through mass purchase, which lowers unit cost--and in fabrication time, which is significantly shorter than in standard construction (the exact amount saved depends on on-site labor rates for the job).

ResCore is a research prototype of a self-contained, manufactured, residential utility wall that provides all the electrical and mechanical connections in one small area. This simple wall incorporates a complete rough-in of electricity, gas, phone, and water utilities, along with exhaust, combustion makeup air, and refrigerant lines. It is fabricated off-site and delivered ready-made to the construction site. Mobile home and modular home manufacturers have used this type of wall for many years to save on construction costs; now other builders can benefit from similar savings.

Low Costs and Other Benefits ResCore walls feature a layered manufacturing technique that allows each major component group (HVAC, structural, cold water, hot water, drain) to be built as a subassembly and brought together for final assembly. The two structural layers are separated by nonconductive bridging that adds strength and allows copper plumbing (if required by code) to be isolated from galvanized studs. The bridging also makes it possible to attach plumbing pipes and other systems to the frame.

Prefabrication can be accomplished at a relatively low capital cost. The exact cost depends on the number of units to be built and the level of mechanization desired; higher-capacity and more mechanized fabrication will have higher capital costs.

The ResCore wall arrives on the building site intact--no assembly is required. The walls are delivered on flatbed trucks or trailers; wooden triangular braces are used to steady them if they are shipped vertically. Holes in the standard metal studs serve as holders for lifting rods during unloading. Unloading can be done by about four average-sized people. Larger, multiwall units can be moved and set by four to five people. Unloading, positioning, and installing the walls, and connecting the services, takes about two hours.

The system was conceived as a way to provide a mass-produced core unit for kitchen, laundry, bathroom, and utility room construction. Along with lowering construction costs, the goal was to increase quality, speed construction, and provide better overall housing value for the cost-conscious, low- to middle-income home buyer. The impact of the ResCore on energy use was investigated during the course of the project. However, although modest energy savings were projected, these savings were attributed to the efficient building layout rather than to the ResCore walls.

Prototype Evaluations The Department of Industrial Design at Auburn University in Auburn, Alabama, designed, developed, and installed three prototype ResCore systems in 1996 and 1997. Their final report on the project was released in September 1998. The first of the prototypes was installed in September 1996 in Opelika, Alabama, in a Habitat for Humanity home. It was a single-wall unit with layered construction. The unit measured 8 inches x 8 ft x 15 ft and weighed just under 200 lb. It served as a shared wall for a kitchen, bath, laundry, and utility room, providing utility service for all four rooms as well as providing the electrical load center for the house.

The other two prototypes were installed in October 1997 in Habitat for Humanity homes in Plains, Georgia. These designs differed from the first prototype in that they provided the utilities not only in a main utility wall, but also in a series of adjacent and connected walls, in order to address the more complex floor layout of the houses. One of the houses was traditional stick-built construction; the other was a structural insulated panel system (SIPS).

Several energy efficiency features were evaluated for use in the prototypes. These included heat or cold recovery methods, efficient domestic hot water distribution, combined equipment (such as HVAC and hot water), and use of combustion makeup air from the outside rather than from the conditioned space.

Waste recovery methods from hot wastewater and hot exhaust air proved not to be cost-effective, because of the relatively small amount of energy being used in the homes and the intermittent nature of most of the waste energy sources. While hot-water distribution losses were minimized by using shortened distribution runs in the ResCore wall, adding pipe insulation was not cost-effective and would have made it difficult for code inspectors to gain visual access to the piping.

The use of outside air for combustion equipment was considered cost-effective, but because natural gas was not available for the three prototypes that were installed, the houses were all-electric and did not have this feature.

Market Applications The report on ResCore shows that the wall has great potential for saving money in the marketplace. As of late 1998, there was some interest in using ResCore walls in new construction projects.

One builder in the Chicago area and one in the Southeast were interested in investigating the applicability of ResCore to their entry-level houses. The builders felt that lowering costs would significantly increase the number of people who will be able to qualify for the houses, which in turn will greatly increase the builder's market share in entry-level homes. In addition, a large Habitat for Humanity affiliate in the Southeast was considering ResCore for use in its housing for low-income residents.

--Deborah Rider Allen
Deborah Rider Allen is a freelance writer in Richmond, Virginia. Robert Wendt of Oak Ridge National Laboratory contributed to this report.

The ResCore project was funded through a research subcontract from the Department of Energy and was administered by Robert Wendt at the Oak Ridge National Laboratory (ORNL). For additional information on ResCore walls, contact Clark Lundell, Department of Industrial Design, 103 O.D. Smith Hall, Auburn University, Auburn, AL 36849-5121, Tel:(334)844-2369; or Robert Wendt, Advanced and Industrialized Housing, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6070, Tel:(423)574-0260.


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