Issue link: https://cp.revolio.com/i/1121626
Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values Page 14 It is apparent that the water absorption of EPS products is relatively consistent over the 15 years of data that are available. The average water absorption of the EPS data collection is 2.2 % by volume with a range of 0.1 - 5.9% by volume. EPS products absorb some water during extremely wet conditions, but moisture is liberated during dry conditions. The water absorption of XPS products appears to be relatively low within the first five years, but it increases significantly when considering the data at 15 years. The average water absorption of the XPS data collection is 2.6% by volume with a range of 0.0 to 6.3% by volume. The data demonstrates the initial water absorption of XPS is low, but over time water accumulates in the XPS. It is notable that the average results in Figure 7 are lower than data published by The Dow Chemical Co. 27 , where it appeared that the water absorption for XPS is higher in long-term highway applications as shown in Figure 8. Figure 8. Water Absorp on of XPS over me in North American Highway Installa ons 27 8 7 6 5 4 3 2 1 0 0 2 4 6 8 10 12 14 16 18 20 Years Water Absorption, % by Volume Based on the analysis of the North American data, it is reasonable to approximate the long-term moisture absorption for both EPS and XPS in below-grade building applications at 3% by volume. It is reasonable to anticipate that water absorption is negligible in a properly installed wall or roof assembly. The combination of water absorption by volume along with equation 1 can be used to determine F H20 in Table 7. Equation 1 F H2O = 1/e (a•Moisture vol%) where a = 4.0 for EPS and 2.5 for XPS and e is Euler's number, 2.71828.