PIMA Publishes R-value Evaluation of Polyiso Roof Insulation
Originally published by: PIMA — April 14, 2016
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PIMA has published a new Performance Bulletin that supports and validates the use of PIMA member published LTTR values as the most reliable measure of polyiso thermal value for building owners, designers, specifiers, and contractors. The 2016 edition of the Roofing Manual of the National Roofing Contractors Association (NRCA) includes a recommendation for the use of an arbitrary unit R-value of 5.0 for all thicknesses and configurations of polyiso roof insulation in lieu of current ASTM C-1289 Long-Term Thermal Resistance (LTTR) values as published by PIMA.
PIMA stands by the well established Long-Term Thermal Resistance (LTTR) values published by PIMA members for over a decade. LTTR:
Remains the most reliable and relevant measure of long-term polyiso roof insulation R-value for the building designer, specifier and roofing contractor.
Is supported by years of scientific study conducted by leading research organizations, including Oak Ridge National Laboratory (ORNL) and the National Research Council of Canada (NRC-CNRC).
Has been established as a reliable national consensus standard both in the United States (ASTM C1289) and Canada (CAN/ULC- S704) and is incorporated within all North American building codes as the designated measure of polyiso roof insulation performance.
As a leader in the manufacture of energy-efficient roof insulation, PIMA encourages building owners, designers, specifiers, and contractors to rely on thermal performance information based on recognized national standards and validated by a recognized third party. In the case of polyiso roof insulation, the most widely recognized standard is ASTM C-1289 “Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board.” According to this standard, the appropriate means of measuring the thermal value of polyiso roof insulation is LTTR as currently published by PIMA members.