Comparing polyiso R-values
Because polyisocyanurate insulation manufacturers recently changed how they determine and report thermal-resistance properties for their products, there now is an additional set of R-values being associated with polyisocyanurate insulation products. This has caused some confusion in the marketplace, and I will attempt to explain and clarify the situation.
On Jan. 1, polyisocyanurate insulation manufacturers began to use the long-term thermal resistance (LTTR) method for determining and reporting thermal-resistance properties of permeable-faced polyisocyanurate insulation products. (For additional information, see "An end to a debate?" November 2002 issue.)
Previously, polyisocyanurate insulation manufacturers typically tested and reported R-values for their products using PIMA 101, "Roof Insulation Specimen Conditioning Procedure" (previously RIC/TIMA 281-1), which is a six-month conditioning procedure for reporting R-values.
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