Curious Findings About Polyisocyanurate

By: Doug Wehrwein, Sales Representative – Architectural Products


It’s interesting and confusing at times, to analyze all the new test results and information about various roof insulation products.  Over the years polyisocyanurate has been the predominate insulation material used in commercial roofing.  I find it curious that polyiso remains the leader in spite of the fact their published R-values have been declining over the decades.  Back in 1975 they boosted R-8.0 per inch, and in 1985 the R-value became 7.2 per inch.  Then after a few more decades of decline the polyiso R-value recommendation according to Mark Graham, the NRCA’s associate executive director of technical services,  it is suggested R-5.0 per inch be used for polyiso when used in climates zones where heating conditions are prominent.  During these 4 decades of polyiso’s declining R-values their costs have continued to escalate.  You’re paying more for a lesser R-value.

Now there is a new NRCA report indicating that the Polyisocyanurate Insulation Manufacturers Association (PIMA) polyiso LTTR values may not even be reached.   According to additional R-value testing done by the NRCA in late 2014 an average R-value of 5.555 was recorded at 75 F, only close to the R-5.7 as recommended by the Polyisocyanurate Manufacturers Association.   Additionally, testing revealed that the R-values of polyiso were diminished by as much as 27% at temperatures both higher and lower than 75 F, when thermal insulation is most necessary.

Over these same 4 decades expanded polystyrene (EPS) rigid insulation has maintained constant R-values. For example, the R-value for Type II EPS is and always has been 4.6 per inch, and has continued to remain the lowest cost rigid foam insulation.  In addition to EPS’s impressive R-value retention,  EPS can minimize the number of pieces handled because it can come in pieces as thick as 36” and in tapers from ½” to 36”.  Compressive strengths are available from 10 to 25 psi.

ACH Foam roof insulation has many UL Listed assemblies to meet all your roof insulation needs.  Hybrid roof insulation assemblies incorporating EPS will also allow for Full System Warranties.

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