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Most energy saving features pay off in the long run. However, many builders hesitate to make the up-front investment in energy efficiency. Solving this first-cost problem was one goal of a demonstration project conducted by the Center for Housing Innovation at the University of Oregon.

"Our goal was to build a single-family home that met a high standard of energy efficiency," says G.Z. "Charlie" Brown, Director of Energy Studies in Buildings Lab. "However, we wanted the construction cost to be $2,000 less than a conventional energy efficient house."

Two versions of the design were prepared. Both met the energy standards of the Super Good Cents program operated by the Springfield Utility Board in cooperation with the Bonneville Power Administration. The "reference house" was conventionally-framed while the "demonstration house" used structural foam core panels. Panels were selected as the alternative approach, because they were highly energy efficient and promised significant construction cost savings.

"Our initial analysis showed the panel house to be $3,500 more than the reference house," says Brown. "By making design modifications, we were able to cut over $4,300 from the demonstration house's cost estimate."

Panels

A structural foam core panel looks like a sandwich with oriented-strand board (OSB) on the outside and foam insulation on the inside. (See August 1990 for more information.) Panels for the demonstration were donated by AFM Corporation, maker of the R-Control brand.

Using panels reduced the amount of framing lumber by 55 percent. On the other hand, the house contains considerably more OSB than a framed house. Overall, the demonstration house used 5 to 10 percent less wood than the reference house would have used.

"We made several changes to the panels that reduced cost or improved strength," says Brown. Instead of OSB on both sides of the wall panels, they specified plywood siding on the outside and OSB on the inside. That saved $325 in OSB cost.

Brown ordered panels that were thicker than those normally used: 6 inches (R-22) for the floor, 8 inches (R-30) for the walls and 10 inches (R-38) for the roof. Extra thickness helped meet the ambitious energy goal with little added cost.

The researchers attempted to get the best use of material by careful building design. For example:

Tested Energy Savings

Energy performance has already been tested several ways. A co-heating test--in which the power consumption of electric heaters is recorded--showed the heat loss rate to be nearly identical to design estimates. That means the house is about 40 percent more efficient than one built to Oregon's strict energy code.

Researchers also inspected the building with a thermographic camera that allowed them to see "hot spots" from the outside. As expected, the panels showed consistently low heat loss with virtually no insulation gaps or other thermal defects.

Air tightness was measured with a blower door. Results showed air leakage of just .07 air-changes per hour (ACH) under natural conditions. Newly-built conventional houses range from .25 to .50 ACH.

The house was wired for extensive monitoring. Researchers will continue to collect data from the house for one year.

Construction Savings

Material costs for panels are generally higher than lumber and cavity insulation. For panels, the savings comes in labor. Using panels reduced labor to build the shell by 30 to 35 percent. Saving time saves money only if that time is put to good use, such as completing more jobs. This suggests that high-volume builders should be in the best position to capitalize on these savings.

Location also has a big impact, because labor and material costs vary from place to place. Areas with higher labor costs will benefit more from labor savings. Panel costs also vary. The Midwest has a high concentration of manufacturers, which creates a competitive panel market. So, panel prices are lower in the Midwest than other regions.

There's also a learning curve. "We estimate that labor costs will drop 20 percent once the builder is familiar with the system," says Brown. That kind of savings makes business sense for the builder and improves the energy efficiency of housing at the same time.