Fiberglass Batts – Labeled vs. Installed Performance

Summary:
Oak Ridge National Laboratory research shows that “perfectly installed” batts lose 11% of their R-Value, and that “commonly installed” fiberglass batts lose 28% of their labeled R-Value.
This study confirms tests conducted 20 years ago by fiberglass manufacturers, and reveals the surprisingly large disparity between the labeled R-Value and the installed R-Value of fiberglass batts


What Was Measured:
The R-Value results presented here are the clear wall R-Values, which André Desjarlais of Oak Ridge explains, “includes the studs, top and bottom plates, shethings and exterior facade… It does not include additional structural components around details such as corners, windows, etc.”
“The clear wall R-Value… represents the area of the wall containing insulation and only the necessary structural member away from all interface details.”


Why:
“To address the number one wall research need… whole wall performance was ranked by 270 private building industry contributors as the most important public sector R&D need to accelerate the development and application of energy-efficient building walls.”


How:
Full-size walls were constructed and tested to determine their thermal conductivity.


What Did They Find?:
The highest tested R-Value for “R-19” labeled batts was R-17.4 for batts before they were installed. From there, the test results dropped to R-17 and then R-13.7


So the question is: Can’t R-values be used to compare insulation systems?
R-values are a good starting point – but they are the results of small, meticulously prepared laboratory samples and do not necessarily reveal how an insulation system performs once installed in actual buildings. Different insulation systems with the same laboratory “R-value” can deliver much different levels of comfort and energy efficiency