Issue link: http://cp.revolio.com/i/1121626
Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values Page 17 Building insulations are subjected to a wide range of temperatures and moisture conditions during their service life. It is important that R-values are maintained since the purpose of insulation is to isolate a building's interior environment from either warm or cold exterior conditions. Any deterioration of the R-value could lead to increased heating or cooling costs. After consideration of the impact of age, temperature, and moisture on both EPS and XPS, the following conclusions were apparent: • The R-value for EPS is constant over time, but the R-value for XPS decreases by approximately 14% over 50 years. • The R-value for EPS and XPS increases as the mean temperature decreases below 75°F (24°C). At a mean temperature of 40°F (4°C), the R-values for EPS and XPS increase by approximately 10%. • The R-values for both EPS and XPS decrease by approximately 10% due to water absorption of 3% by volume in below-grade applications. A methodology was provided to calculate the effective R-value for specific building applications when a detailed analysis is desired. An example of above-grade summer walls was shown with a reduction in R-value for EPS of 3-4% and a reduction in R-value for XPS of 16%. An example of above-grade winter walls was shown with an increase in R-value for EPS of 10% and a reduction in R-value for XPS of 7%. An example of below-grade walls was shown with a reduction in R-value for EPS of 7% and a reduction in R-value for XPS of 17%. The magnitudes of the adjustments to the R-values were not extremely large, but it was apparent that the R-value performance of EPS was better preserved than the R-value of XPS. The prime contributor to this difference was the loss of R-value as the XPS products aged. Summary