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Home Energy Magazine Online March/April 1999
trends
in energy
Prefab Utility Walls Save Up-Front Costs
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| 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. |
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| 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 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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