Think of it like this! You buy a new vehicle and its estimated fuel economy is 10 liters per 100 kilometers. After six months of driving it actually consumes 15 liters per 100. Analogy: The Labelled R-value of insulation is its estimated fuel economy, effective R-value is its actual performance in real world wall assemblies, tested in winter like conditions.
6″ fiberglass insulation has a labelled R-value of 20. However, in wood frame wall assemblies, under cold climate conditions, it performs effectively at R-15. In steel frame assemblies it performs at only R-7, or 63% less than its labelled R-value. Using the vehicle analogy, it’s like consuming 23 liters per hundred as opposed to 10 liters per 100 that you expected.
Until recently, insulation products have been tested on their own, at temperatures that produce their best R-value performance. More or less, it’s similar to testing the fuel economy of a vehicle going downhill. On the other hand, testing insulation to its effective R-value in actual wall assemblies, in cold “real world” environments, is like testing the fuel economy of a vehicle going uphill. For cold Canadian winters, insulation needs to be tested going uphill. Next time you purchase insulation, ask for its effective R-value rating tested in Canadian winter like conditions.
To learn more about cold climate effective R-value testing, go to quiktherm.com