Insulation and the R-value myth

Insulation is installed in a building to minimize unwanted heat loss or heat gain through the building envelope. Types of insulation include cellulose, fiberglass, rock wool, polystyrene, vermiculite and polyurethane foam. R-value measures the thermal resistance a specific insulation material provides.  R-values may be misleading because heat loss or heat gain will ultimately depend on the thermal resistance of the overall wall system, not just on the insulation.

R-values are measured under laboratory conditions that are seldom found in the real world.  Oak Ridge National Laboratory research shows that the highest tested R-value for R-19 labeled fiberglass batts was R-17.4 for batts before they were installed. From there, the test results dropped as low as R-13.7 when the batts were installed using common installation methods.  Non-solid insulations like fiberglass derive their thermal resistance from trapped dead air.  The effects of moisture and/or air movement disturbing this dead air are not taken into account in the laboratory and will further diminish the R-value of fiberglass in real world applications.

The major components that will determine the overall thermal performance of the building envelope are insulation, air tightness and moisture tolerance.  Closed cell sprayed polyurethane foam (ccSPF) is the only product that will address all three of these factors with one application.  ccSPF has an R-value of R-6.5 per inch, almost double other common insulation materials.  In addition, when installed at a thickness of at least 2 inches, it provides a superior air and moisture barrier.



Resource Links

Insulation Energy Savings: Key Issues and Performance Factors
Is Fiberglass a Carcinogen?