XPS Insulation Tests Confirm Diminished R-Value When Exposed

Originally posted on ConstructionRepair.net

EPS Industry Alliance release new comparative test results

The EPS Industry Alliance (EPS-IA) recently completed a series of tests on extruded polystyrene (XPS) to examine the effects of moisture absorption and R-value in different field applications. Two new technical resources look at the behavior of rigid foam insulation exposed to water, specifically related to the materials drying potential and R-value retention.

When evaluating XPS material samples extracted from roofing and below grade applications, in these long-term installations, XPS did not maintain its initial R-value.

Buildings have been and always will be exposed to moisture. It is not a good thing or a bad thing; it is merely another component of the building design process. When materials are exposed to moisture, the ability to dry is key to maintaining thermal resistance.

This issue is addressed in Drying Potential of Polystyrene Insulations Under Extreme Environmental Cycling Conditions , which evaluates the free-thaw cycling effects on rigid foam plastics as prescribed by ASTM C1512. The test results indicate XPS exceeds the recommended water absorption threshold dictated by ASTM C578 by a factor of 2.4, and, test data rendered by Intertek Testing Services show that in-situ water absorption from XPS samples taken from four different locations is widely variable from 5 – 60% by volume.

Standardized laboratory testing, while not intended to replicate in-situ, real-world conditions, substantiate expanded polystyrene (EPS) performance claims to deliver consistent R-value in building environments that may be exposed to moisture. XPS producers claim its lower moisture absorption rate is a benefit; however, this is based on flawed logic. XPS R-values begin to deteriorate at only 0.03 percent, meaning its tolerance for water absorption is extremely low.

This phenomenon is demonstrated in the test results published in XPS Insulation Extracted After Field Exposure Confirms High Water Absorption Diminished R-value . On the other hand, EPS demonstrates excellent drying abilities and has a much higher tolerance for moisture exposure while still delivering the same R-value throughout the life of the building.

Expanded polystyrene exhibits superior moisture-related performance properties over XPS. It has higher vapor permeability, meaning it helps promote drying in a wall system. As shown in the EPS-IA technical bulletins, EPS is inherently more capable of tolerating moisture absorption than XPS.

Even at 3.0 – 4.0% moisture absorption, expanded polystyrene insulation delivers consistent R-value of 3.1 – 4.3 per inch.

When evaluating rigid foam insulation performance properties, non-standardized testing, modified test methods or testing not intended for the materials being evaluated should be viewed with skepticism. EPS-IAs new information comparing EPS and XPS moisture absorption and R-value retention is based on testing conducted by a third-party, certified testing laboratory and relies on industry recognized standards ASTM C1512. ASTM C518 and others.

EPS-IA is confident these new documents will be a valuable resource for architects, contractors and consumers that are seeking the best possible insulation for their construction projects. For more information on expanded polystyrene and the results of EPS-IAs new test results please contact Betsy Steiner, EPS-IA Executive Director, at emsteiner@epsindustry.org or 800-607-3772.

New Below Grade Data Released: EPS vs. XPS Insulation

The EPS Industry Alliance (EPS IA) has released NEW moisture absorption data regarding XPS, moisture absorption and the effects on R-Value through the latest Technical Bulletin, EPS Below Grade Series 105:   XPS Insulation Extracted After Field Exposure Confirms High Water Absorption & Diminished R-Value, March 2014 (pdf)

EPS IA March 2014

EPS Below Grade Series 105, March 2014

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 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 in the summary.  

Read Full Technical Bulletin Summary (pdf)

“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.”

 

Read more on the technical background expanding on the moisture resistance comparison between EPS and XPS conducted in the 2008 test program: