Specifications

LTTR Calculator

Fastening Patterns

Certified Drainage Program (CDP) & Field Services

Case Studies

WHAT IS LONG-TERM THERMAL RESISTANCE (LTTR)?

LTTR is the most advanced, scientifically supported method (based on ASTM C 1303-95) of predicting the Long-Term Thermal Resistance of polyisocyanurate insulation products, such as the HCFC-Free, Green Zone Approved Atlas Products featuring ACUltra Technology. Long-Term Thermal Resistance (LTTR) provides specifiers, design professionals, and roofing contractors many advantages, including:

• A Long-Term Thermal Design Value (15 year time-weighted average)
  
  
• A better understanding of thermal performance of foam. Click Here for a detailed look at the Long Term Thermal Resistance of Pentane Blown Polyisocyanurate.
  
  
• An advanced test method, based upon consensus standards used by both US and Canada
  
  
• A technically supported, prescriptive method to measure the Long-Term Thermal Resistance (LTTR) of polyiso foam insulation
  
  
• Long-Term Thermal Resistance (LTTR) values are required in the mandatory annex of ASTM C 1289-02
  
  
• See the following LTTR Technical Bulletin for more information

The roofing industry now has a definitive standard for predicting Long-Term Thermal Resistance (LTTR) values. The new Long-Term Thermal Resistance (LTTR) values become effective July 1, 2002 in Canada and January 1, 2003 in the United States.

How To Use The Calculator: Select the desired Long-Term Thermal Resistance (LTTR) value from the pull down menu below. The calculator will automatically determine the required thickness and the minimum number of layers needed to achieve the Long-Term Thermal Resistance (LTTR) value selected for each product listed. Additionally, the calculator will reveal the actual Long-Term Thermal Resistance (LTTR) value achieved:

*Atlas recommends multi-layering when desired insulation thicknesses are greater than 2.7".
See the following Multi-Layering Technical Bulletin for more information.