Issue link: https://cp.revolio.com/i/1121626
The R-value of EPS is constant over time, and the R-value of XPS decreases over time. Aging Similar R-value reductions occur for EPS and XPS in below grade applications. Moisture The primary purpose of insulation is to isolate a building's interior environment from either warm or cold exterior conditions. In many building applications, polystyrene foam insulation is protected from moisture, and the R-values determined under dry laboratory conditions are appropriate. This document provides a methodology that uses short-term, laboratory-determined R-values with adjustment factors to account for the long-term conditions of buildings when a more detailed analysis is desired. The focus is on the insulating or R-value performance of expanded polystyrene (EPS) and extruded polystyrene (XPS) foam products used in long-term building applications. A methodology is presented in which the laboratory-determined R-value is multiplied by three adjustment factors to determine the long-term effective R-value of installed insulation. After considering the impact of age, temperature, and moisture on both EPS and XPS, the following conclusions are drawn: • The R-value for EPS was constant over time and the R-value for XPS decreased by approximately 14% over 50 years. • The R-values for EPS and XPS increase when 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 the absorption of water in below-grade applications. The magnitudes of the adjustments to the R-values were not extremely large, but the analysis demonstrated that the R-value performance of EPS was preserved better than that of XPS when all factors were considered. The prime contributor to this difference was the loss of R-value by XPS that occurred with age due to out-gassing of blowing agents. Executive Summary POLYSTYRENE FOAM INSULATION IN LONG-TERM BUILDING APPLICATIONS Effective R-values The R-value of EPS and XPS increases when the mean temperature decreases below 75°F (24°C). Temperature