STUDIES SHOW THE ENERGY EFFICIENCY OF STRUCTURAL INSULATED PANELS (SIPs)
Energy Efficiency Affects Market Value
A study funded by the EPA shows that energy efficiency increases the market value of homes. This study, “Evidence of Rational Market Values for Homes Energy Efficiency,” was conducted for the EPA by ICF, Inc. It was published in the October 1998 issue of The Appraisal Journal and showed:
- Energy-efficient homes have a higher market or resale value regardless of how long you own your home.
- Home value increases $20 for every $1 reduction in average annual utility bills.
R-Values: SIPS vs Stick Built
The study reports that the foam core of SIPs provides R-values of 4 to 7 per 1 inch of thickness. This results in excellent energy performance in the walls and roof. For comparison, a 4-1/2 inch thick SIPs wall is often used as a substitute for a 2×4 stud wall. Both walls have 3-1/2 inches of foam and are 4-1/2 inches thick overall. However, the SIPs wall has R-values of 14-25, while the stud wall with fiberglass insulation has R-values of 11-15.
The study goes on to say that the overall R-value of the stud wall must then be down-graded. This is to account for the areas lacking insulation because of the space taken up by the stud framing. This space can be as great as 25%. This issue is then compounded because the fiberglass or cellulose insulation will settle over time. This creates more dead air space within the walls. As a result, this dead space can also lead to areas for dust and other pollutants to gather. It could also lead to drafty conditions around windows, doors, electrical outlets and more. On the other hand, these problems are solved with the ridged foam core of SIPs panels. Their foam core will not settle or compress so R-values will remain constant over time. The result, as indicated by the “Thermal Envelope Compliance Guide” to the “Model Energy Code” is striking. It reports, the overall R-value of a 2×4 stud wall with 3” of R-13 fiberglass is R-13.1. Whereas, A SIP wall with OSB encasing 3” of extruded polystyrene foam is R-20.
Energy Savings Potential
However, these R-Value calculations don’t tell the entire story. SIPs appear to outperform stick framed walls even if they are assumed to have the same R-values. This may be due to the previous discussion of the issues of settling and dead air spaces when you compare ridged foams to fiberglass and cellulose insulation. These issues were clearly illustrated in a field test conducted by the Florida Solar Energy Center (FSEC). This study was conducted under sponsorship of the US Department of Energy. It involved two identical houses built side by side in Louisville, Ky. They were built at the same time and by the same builder. One had conventional framing, the other was built with SIPs. However, wall and roof thicknesses were adjusted so that both had the same calculated R-values. Both houses were monitored for heat loss performance. It was found that the SIP house dramatically outperformed the frame house. More importantly, forecasted seasonal heating energy savings showed a 14-20 percent savings for the SIP house in Kentucky’s climate. In the published report, the researchers stated that, “…there seem to be other factors, which remain unaccounted for, which cause the panel house to use less heat energy.”
In another study performed in 2008-2009, Oak Ridge National Laboratory performed a comparative test between a SIP-built house and a stick-built house. The stick-built house used standard 2×4 framing and fiberglass insulation. The SIP-built house used 3 ½” foam core OSB panels. The SIP-built house used 53% less energy compared to the stick-built house.
The outcome of these studies show a considerable energy savings due to the insulating performance of these SIP homes. As a result, the U.S. Department of Energy, and the Environmental Protection Agency (see EPS/DOE Energy Star Program) are supporters of the use of SIPs in housing construction. It’s clear that SIPs built homes are more comfortable to live in. They are also far more economical to own and operate than conventional built homes. Homeowners throughout the US are experiencing benefits through lower heating costs, greater comfort, and draft-free homes.
SIPs built homes also offer savings in ecological terms. The use of SIPs panels minimizes the use of dimensional lumber which reduces stress on old-growth forests. Furthermore, the energy efficiency of the SIPs panel system also reduces dependence on non-renewable fuel resources. These are all important considerations for the new homeowner. Plus, SIPs homes are much more attractive to lenders, tenants and buyers. Lastly, one more important consideration in today’s construction industry is the speed and simplicity of construction.