The EPS Industry Alliance publishes technical bulletins to help inform building professionals on the performance characteristics of expanded polystyrene (EPS) building products. The information contained herein is provided without any express or implied warranty as to its truthfulness or accuracy.
A test program conducted in August 2008 evaluated the field performance of expanded (EPS) and extruded (XPS) polystyrene foam insulation in a side‐by‐side, below grade application following a continuous 15‐year installation period.
When water and R‐value retention were compared between EPS and XPS, the results demonstrated that EPS insulation outperformed XPS insulation with better R‐value retention and a lower moisture absorption.
In 2013, an independent testing laboratory was again commissioned to evaluate the R‐value and water absorption from XPS insulation samples extracted from several field locations and applications. A summary of the 2013 test results are shown in Figure 1 and reconfirm there is no correlation between the results from standardized laboratory test methods and actual field exposure for XPS water absorption. Further, the significant loss of R‐value associated with XPS water absorption is shown.
Studies show that as much as 25% of energy loss from a structure can be attributed to a lack of insulation. Insulation R‐value is directly correlated to maximum energy efficiency in a building envelope; higher R‐values translate into increased savings. It is important to understand that in‐situ water absorption can diminish the thermal performance of building materials and designers must account for this when evaluating different insulation choices.
Standardized Laboratory Water Absorption Test Methods DO NOT Predict Long‐Term R‐value Performance
The most common laboratory test methods to evaluate moisture absorption call for partial or full submersion conditions that do not replicate exposure in field applications. Standardized laboratory submersion test methods are typically conducted with 1‐inch thick samples that are submerged for 24 or 96 hours. These basic laboratory test methods were not developed for predicting in‐situ performance, but are intended for use in specifications as a means of product quality control.
Building insulations are subjected to a wide range of conditions and must maintain their performance over extended periods of time. In this context the value of in‐situ test data is crucial and more important than basic laboratory test methods.
To investigate the in‐situ performance of extruded polystyrene (XPS) insulation, an independent laboratory was commissioned to evaluate the field performance for various applications being used in different climates. The XPS samples were excavated under the supervision of the independent laboratory to conduct R‐value and water absorption measurements. Samples from four different locations and applications were selected for testing. Two specimens were evaluated from each location. The R‐value retention and moisture absorption percent for the individual samples were analyzed.
Specimens were tested for thermal resistance using ASTM C518 “Standard Test Method for Steady‐State Thermal Transmission Properties by Means of the Heat Flow Apparatus” immediately after excavation. Moisture content was determined by measuring the sample weight at the time of removal and again after being oven dried.
Standardized Laboratory Water Absorption Test Methods DO NOT Predict Long‐Term R‐value Performance
It is important to recognize that the successful use of polystyrene foam insulation depends upon its correct installation using good building practice. In below grade applications the success of the overall system depends, to a large extent, upon provision for adequate drainage of water away from the foundation system. The following design considerations should be taken into account for below grade applications:
The long‐term application of XPS insulation below grade results in a higher water retention and greater loss of R‐value than reported when using standardized laboratory test methods. Water absorption results for XPS using ASTM C2723 cannot be correlated to the in‐service performance of extruded polystyrene foam insulation. Material specifications such as ASTM C578 and CAN/ULC‐S701 cannot provide all of the answers that a designer may need. These specifications provide physical property requirements for the various EPS and XPS insulation types most commonly used. In many cases, end use applications require unique physical properties and manufacturers have products to meet these needs; designers should consult with manufacturers when a particular application requires specific material properties.
Third‐party research published by Oak Ridge National Laboratory in April 2012 further validates the findings of Table 1, indicating XPS below grade systems can experience a 10‐44% loss of energy savings performance when subjected to moisture accumulation in the range of 8% ‐ 16%. This study, Measurement of Exterior Foundation Insulation To Assess Durability in Energy Saving Performance, evaluated six exterior insulation systems spanning installation periods of 9 months to 15 years.
The EPS Industry Alliance publishes technical bulletins to help inform building professionals on the performance characteristics of expanded polystyrene (EPS) building products. The information contained herein is provided without any express or implied warranty as to its truthfulness or accuracy.
