Letters

PIMA disagrees with LTTR criticism

I read with interest NRCA Associate Executive Director of Technical Services Mark Graham's article "Testing LTTR," January issue, page 30.

The Polyisocyanurate Insulation Manufacturers Association (PIMA) has had a collegial relationship with NRCA working together on issues important to the roofing industry. In addition, since 2003, PIMA has been a strong proponent of the long-term thermal-resistance (LTTR) concept. Our members were the first—and currently are the only—foam insulation manufacturers to embrace a scientifically supported method for depicting long-term thermal performance. Therefore, it was disappointing and baffling that PIMA and its members never were offered the opportunity to participate in the "study" Graham describes.

The article also fails to educate readers about two important programs under way at ASTM International that are exploring even better understanding and refinement of LTTR value methods. The first program, which is looking at the bias of LTTR, began three years ago and will be completed in 2008. The second program, under the leadership of Oak Ridge National Laboratory, Oak Ridge, Tenn., is developing a prescriptive version of ASTM C1303, "Standard Test Method for Estimating the Long-Term Change in the Thermal Resistance of Unfaced Rigid Closed Cell Plastic Foams by Slicing and Scaling Under Controlled Laboratory Conditions," which will result in an ASTM International LTTR value method. Finally, ASTM International's C1303 Task Group has prepared a well-defined study that will include polyisocyanurate and extruded polystyrene and should begin in the near future.

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