Updating values for polyiso

The January issue of The Construction Specifier included the article, “Impact of Advancements in Model Energy Codes,” by Jared O. Blum. We received the following letter to the editor from Tim Merchant of the EPS Industry Alliance, an organization representing those in the expanded polystyrene community.

The EPS Industry Alliance has always supported informative articles that advance the knowledge, proper use, and application of foam insulation. That said, the article makes some inaccurate claims regarding R-value of polyisocyanurate (polyiso) insulation that we would like to address.
The chart on page 68 lists the R-values of several foam insulations, including polyiso, which it says has an R-value of 6. This is in alignment with ASTM C1289-13, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board, and Underwriters Laboratories of Canada (CAN/ULC) S770-09, Standard Test Method for Determination of Long-term Thermal Resistance of Closed-cell Thermal Insulating Foams as of your publication. However, new testing methods developed in 2013 have shown the R-value of 25 mm (1 in.) of polyiso is 5.6—seven percent less than the measure of previous standards.
Last June, the Polyisocyanurate Insulation Manufacturers Association (PIMA) announced it would be updating its QualityMark-certified R-value program to reflect the new data, which was determined using a new test method for finding long-term thermal resistance (LTTR). The new 5.6 R-value rating was to be incorporated in Canadian and U.S. standards as of January 1, 2014. Please keep this in mind for future articles related to the R-value of polyiso insulation.

We asked the article’s author to respond:

ASTM C1289-13 was updated last year, and features important improvements regarding the prediction of long-term thermal resistance value (i.e. R-value) for various polyiso insulation boards. The article published in this issue of The Construction Specifier was originally written before PIMA and its members began reporting LTTR values in accordance with the standard on January 1, 2014 as part the PIMA’s QualityMark program.
To participate in PIMA’s QualityMark certification program, a Class 1 roof is suggested to have a design R-value of 5.7 per inch. It should be noted polyiso is unique in the R-value increases with the thickness of the foam, so 76 mm (3 in.) of polyiso has a higher R-value per inch than 50 mm (2 in.).
Since its founding, PIMA has been active in the harmonization of relevant standards to provide greater continuity in the reporting of polyiso roof insulation thermal values throughout North America. This is why the association implemented the industry-wide QualityMark certified R-value program for rigid polyiso roof insulation in 2004. The update to this standard provides more data to aid in the prediction of long-term thermal performance of North America’s most popular rigid roof insulation.

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