LTTR replaces the older industry-accepted term R-Value, and is the most advanced scientifically supported method (based on ASTM C 1303-95) of predicting the long-term thermal resistance of polyisocyanurate insulation products. This new method provides many advantages to design professionals, including a 15-year, time-weighted average, a better understanding of the performance of foam insulation, and an advanced method based upon consensus standards used by both the United States and Canada. New LTTR values went into effect in Canada July 1, 2002, and will go into effect in the United States Jan. 1, 2003.

The LTTR calculator allows users to select a new LTTR value and then automatically view which Atlas product(s) and thickness(es) will meet the pre-selected value. For more information, go to www.atlasroofing.com.