News From Go Plymouth Foam

LTTR - What does long-term R-value mean

What is your definition of long-term - 5, 10, 25 years? How should we judge the R-value of insulation long-term? LTTR (Long-Term Thermal Resistance) is a measure to quantify a comparative method of R-value in an attempt at trying to help architects, specifiers, builders, inspectors and owners. This measurement is achieved by the test methods ASTM C1303 or CAN/ULC-S770. I applaud the effort of developing these testing to quantify thermal performance, however a major adjustment may need to take place or at least the building industry need to understand these measurements - what they are and what they are not.

Early this year, the National Roofers Contractors Association, made a recommendation to it's members that Polyisocyanurate Insulation revise "its design in-service R-value recommendation to 5.0 per inch thickness." This declaration was the second time Polyisocyanurate's R-value was downgraded in the last 2 years. For some of us "Energy Aficionados," who understand the principles of insulation off-gassing, determined it was time to re-examine LTTR testing (
View Technical LTTR Bulletin).

LTTR really looks at Long-Term Thermal Performance of insulation as 5 years. Do we expect a building to last only five years? How is 5 years a true quantitative analysis of R-value performance?

We do not replace insulation in a building every 5 years, why would we think that is long-term? Most building in the U.S. are built to last 50 years, some 100 years. Long-term R-value should be figured at 50 years… right? We know off-gassing continues to happen after 5 years. Let's re-evaluate what we are doing as an industry and modify Long-Term Thermal Resistance to at least 50 years.