 A material’s R-value is a measure of its resistance to heat transfer. What very few people realize is that building codes do not mandate how R-values are to be determined. So insulation manufacturers design the R-Value of their product in a laboratory using a device known as a “guarded hot plate”, according to common standards such as ASTM C518 or ASTM C177.
This is known as a steady state test because the test samples are completely sealed from air infiltration. In these tests, fiberglass and EPS insulation easily achieve building code minimum R-values. But let’s turn now to the real world, where unlike in the lab, air infiltration is unavoidable.
Pages
Part 1 - R-Values in Today's Building Codes
Part 2 - Designing R-Values: In the Lab
Part 3 - Air Infiltration
Part 4 - "Real Time" R-Values
Part 5 - Oak Ridge National Laboratory Study
Part 6 - Brock University Study
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