U.S. Updates XPS Aged R-Value Rule

With growing recognition of aged R-value for some foam plastics and the use of updated test methods to account for long-term R-value, the U.S. Federal Trade Commission has updated its R-Value Rule (16 CFR Part 460) regarding appropriate marketing claims for thermal insulation performance. The final rule, though not mandating a prescriptive LTTR method, requires that manufacturers publish R-values that fully reflect the effects of aging on their products. The final rule will take effect in October 2019.

To characterize the effective R-value of polystyrene insulation considering the effects of aging and the conditions of application, the EPS Industry Alliance has published a paper, “Polystyrene Foam Insulation in Long-Term Building Applications, Effective R-Values,” that provides a method to estimate the effective R-value by accounting for these factors.

In Canada in 2017, the ULC Standards Committee on Thermal Insulation Materials and Systems approved an updated fifth edition of the CAN/ULC-S701.1, Standard for Thermal Insulation, Polystyrene Boards. This standard specifies the requirements for rigid expanded polystyrene (EPS) and extruded polystyrene (XPS) insulation.

Two changes to the Fifth Edition were significant for providing more clarity on thermal performance. First, this edition removed the conditioned thermal resistance requirements for XPS in favor of requiring the Long-Term Thermal Resistance (LTTR) determined using CAN/ULC-S770-15, Standard Test Method for Determination of Long-Term Thermal Resistance of Closed-Cell Thermal Insulating Foams, for XPS insulation products.

The CAN/ULC-S770 test method is used to determine the LTTR for products that contain a cell gas (other than air) which diffuses over time (foam plastic insulation like XPS that are subject to aging). CAN/ULC-S770 predicts the five-year aged R-value (equal to the 15-year time-weighted average R-value). In contrast, EPS insulation, which contains only air in its closed cell structure and therefore does not age, continues to have its R-value determined by ASTM C518.

The second change mandated that the LTTR, rather than the initial R-value or conditioned R-value, be marked on the XPS insulation products for greater clarity for consumers and designers. These two changes are consistent with the requirements of the building code to use LTTR values in energy calculations for foam plastic insulations that are manufactured to retain a blowing agent other than air for a period longer than 180 days.

The U.S. equivalent to the Canadian S701.1 standard, ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, also contains a requirement that the LTTR be determined and reported for XPS. While reporting is stipulated, no requirement for LTTR labeling and product marking exists in C578.

R-value test standards, specifications, and labeling requirements are critical to providing consumers and designers with information necessary to predict the thermal performance of the insulation product. Without an understanding of aged R-value, consumers, building designers, and specifiers will overestimate the insulation’s performance and underestimate the energy consumption of the building over the lifespan of the building.

The EPS Industry Alliance is the North American trade organization representing the expanded polystyrene industry and focuses on the advancement and innovation of EPS products in construction and packaging.

For more information, please contact Betsy Bowers at (800) 607-3772 or [email protected].  

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