Issue link: http://cp.revolio.com/i/1121626
Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values Page 3 Introduction The primary purpose of insulation is to isolate a building's interior environment from either warm or cold exterior conditions, i.e., to keep a building warm when it is cold outside or to keep a building cool when it is hot outside. R-value, or thermal resistance, is a measure of the ability of insulation to resist the flow of heat. The higher the R-value, the greater the resistance to heat flow. A higher R-value translates into lower heating and cooling costs and reduced pollution. It is very important to understand the differences in the R-values of polystyrene foam insulations in various building applications over time, at various temperatures, and various moisture conditions. The U.S. Federal Trade Commission (FTC) has an "R-value Rule" regarding advertised R-values for insulation materials to consumers 1 . The R-value Rule requires that R-value testing is conducted on samples at a mean temperature of 75° F (24°C). This temperature is not intended to reflect the mean temperature of insulations in building applications but rather to provide a uniform basis that allows consumers to compare different insulations at standard laboratory conditions. Per the R-value Rule, R-values are most often measured using ASTM C518 2 or ASTM C177 3 test methods. Unfortunately, the R-values derived from these ASTM standard laboratory scale tests do not provide a full representation of the performance of insulation in buildings because the tests do not account for the age of the insulation or its exposure to other temperatures and moisture after installation in a building. Standard test methods are available for determining the impact of age 4-6 through methods that estimate the long- term R-values of foam plastics. The ULC and ASTM methods are most commonly used in North America to provide an estimate of the long-term thermal resistance (LTTR) of insulation at five years. The use of a five-year estimate of the R-value is an improvement over the use of a short-term R-value, but it is insufficient for predicting the R-value of extruded polystyrene foam over the life of a building, particularly since building professionals expect buildings to last at least 50 years 7 . It is very important to understand the differences in the R-values of polystyrene foam insulations in various building applications over time, at various temperatures, and various moisture conditions. "