The December 2013 issue of The Construction Specifier included the article, “Out of Sight, Not Out of Mind,” by Ram Mayilvahanan. The feature focused on expanded polystyrene (EPS) and included reference to a particular industry study. In response to the piece, we recently received the following e-mail from John Ferraro, executive director of the Extruded Polystyrene Foam Association (XPSA):
This article included conclusions on the long-term thermal performance of XPS in below-grade applications contrary to more broadly evaluated and accepted industry data. It references a 2009 evaluation published by the EPS Industry Alliance (IA) industry trade organization, then known as EPSMA, and since republished in many forms by EPS-IA members.
In our opinion, the results of this EPS evaluation, which in essence rely on one data point, are not well-supported and are inconsistent with previous significant research conducted in this field. This EPS evaluation also was not independently peer-reviewed within the industry. The data used was reportedly the result of tests conducted by the same test lab and at the same test site, which were apparently employed in two prior studies: Society of the Plastics Industry’s (SPI’s) 1994 report, “Expanded Polystyrene Thermal Insulation Performance in a Below-grade Application” (Twin City Testing Corp.) and AFM Corp.’s 1996 report, “Thermal Transmission and Moisture Content Analyses Conducted on Buried EPS Perform Guard Insulation” (Maxim Technologies/Twin City Testing). There are unanswered questions surrounding the data reliability from these previous analyses that may also carry forward into the EPS evaluation.
The long-term thermal performance of below-grade foundation insulation is an important building design consideration that directly impacts building comfort and energy conservation. We want to draw your attention to a more comprehensive and objective review of the long-term thermal performance of polystyrene foam insulation in below-grade applications that was conducted by the American Society of Civil Engineers (ASCE) 32 Committee during its revisions to ASCE 32-01, Design and Construction of Frost-protected Shallow Foundations.
This committee’s work was documented in the technical paper, “Below-ground Performance of Rigid Polystyrene Foam Insulation: Review of Effective Thermal Resistivity Values Used in ASCE Standard 32-01, Design and Construction of Frost-Protected Shallow Foundations,” which was published in the Journal of Cold Regions Engineering in June 2010.
Based on this critical review of frost-protected shallow foundation designs, the ASCE committee recommends for below-grade vertical orientation (i.e. exterior of walls) using effective in-service design R-value equal to:
● 90 percent of the ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, R-value for XPS; or
● 80 percent of the ASTM C578 R-value for EPS because of the potential for water absorption.
The ASCE committee also recommends for below-grade horizontal orientation (i.e. under concrete slabs) using effective in-serve design R-values equal to:
● 80 percent of the ASTM C578 R-value for XPS; or
● 65 to 67 percent of the ASTM C578 R-value for EPS because of the potential for water absorption.
We believe it is very important to provide your readership and the industry with objective and accurate information to support and facilitate informed choices in building design. By reporting data from a single, non-peer-reviewed, narrow-scope study and ignoring the vast amount of research and experience, this article does not serve the best interest of the industry.