Tech Today

New LTTR values

In June, the Polyisocyanurate Insulation Manufacturers Association (PIMA) announced its QualityMark-certified R-value program is being updated to incorporate a new test method for determining long-term thermal resistance (LTTR). As a result, new LTTR values are going to decrease from current values. If you are involved in the design, procurement or installation of roof systems that include polyisocyanurate insulation, you should be aware of these upcoming changes.

LTTR test method

Since 2004, LTTR values for polyisocyanurate insulation have been reported using PIMA's QualityMark program, which provides for testing according to CAN/ULC-S770-03, "Standard Test Method for Determination of Long-Term Thermal Resistance of Closed-Cell Thermal Insulating Foams."

In 2011, the U.S. product standard for polyisocyanurate insulation, ASTM C1289, "Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board," was updated to reference CAN/ULC-S770's 2009 edition. Use of ASTM C1303-11, "Standard Test Method for Predicting Long Term Thermal Resistance of Closed Cell Foam Insulation," also is permitted.

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