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Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values Page 9 Aging Adjustment Factor The R-value of any insulation should account for the impact of R-value aging when used on buildings with a design life of 50 years. Aging is a process during which certain insulations with captive blowing agents lose those blowing agents over time. Since the blowing agents can contribute to the R-value of certain insulations, the R-value of these types of insulation decrease over time. Extruded polystyrene (XPS) contains a blowing agent that is lost over time, so its R-value must be adjusted. R-value data is limited for XPS insulations in North America beyond five years. However, there are estimates of R-values at five years published in CAN/ULC S701.1. The ASTM C578 standard requires XPS producers to determine and report the LTTR following ASTM C1303 values, but this information is not readily available from XPS manufacturers in the US. However, several publications provide insight concerning the R-value of XPS after longer periods due to the loss of blowing agents 16-19 The R-values of insulations that contain only air do not decrease over time. As shown in Figure 1, the R-value of EPS products is constant over a 50 years. Figure 4 shows the decay of blowing agent HFC-134a in an XPS foam where after 25 years over 90% of the blowing agent has been lost. Since the blowing agent is lost over time, the R-value diminishes over time. Similar information on the loss of the blowing agent also has been published by other researchers. 0 5 10 15 20 25 100 80 60 40 20 0 Age, Years Blowing Agent, % Figure 4. Blowing Agent Loss of XPS 18 As noted, there is limited data from the U.S. manufacturers of XPS, but some short-term data has been published 19 . There also has been recent aged R-value testing conducted on one U.S. manufactured XPS 20 . Figure 5 shows the estimated R-value over time for XPS produced in the U.S. based on recent testing 20 and available research 16-19 on the long term performance of XPS produced internationally. The R-value drops significantly over time below the claimed R-value of 5.0 and is in close agreement with the values provided in CAN/ULC S701.1 at 5 years. Considering all the available data 16-20 , the R-value used in this document to determine the long-term (50-year) aging adjustment factor for XPS is estimated to be 4.3. This value is an estimate and may need adjustment as more data becomes available.