WASHINGTON — The Polyisocyanurate Insulation Manufacturers Association (PIMA) has announced the release of a research report demonstrating that the R-value of polyiso roof insulation shows no significant variation within the average winter and summer temperature ranges across North America.
The PIMA report, titled “Thermal Resistance and Mean Temperature: A Report for Building Owners and Design Professionals,” was developed as a comprehensive response to recent articles that questioned the thermal performance of polyiso roof insulation in colder climates.
The research report concludes that:
• The primary reason for any apparent reduction in polyiso roof insulation thermal value in colder climates is related to the use of an unnecessarily low estimate of “mean reference temperature” to calculate R-values in cold climates. This conclusion is supported by an extensive analysis of historical North American climate data included as an appendix to the report.
• Polyiso roof insulation R-values, when calculated using an adjusted mean reference temperature range indicated by the analysis of North American climate data, appear to be higher than the values suggested by some recent articles and don’t differ significantly from current PIMA member published R-values.
As a result of these research findings, PIMA concludes that roof insulation R-values currently published by its members continue to provide the best guide for building designers seeking prescriptive insulation thermal performance information.
“It is unfortunate that the relevant thermal testing range for polyiso roof insulation appears to have been misinterpreted by some members of the thermal insulation and roofing industries,” said Jared Blum, president of PIMA. “This new report sets the record straight and provides useful thermal performance information for roofing designers and building owners.”
A copy of the research report is available for download at PIMA’s website (www.polyiso.org) and from PIMA members.