In the world of building construction, improvement, and insulation, we talk about R-value all the time. Usually, we talk about it as if it’s a constant number. We see R-19 stamped right there on the product, so that’s what it is, right? Well, did you know that the R-value of insulation is not a constant?
What Is R-Value?
R-value is a measure of resistance to heat flow through a given thickness of material. R-value is important, but it’s just one of a few key factors that determine the effectiveness of an insulation material. The R-value is tested in an air-tight vacuum chamber, which means that typical insulation materials like fiberglass and cellulose do not actually perform with that value unless paired with intense air sealing measures.
How Is R-value measured?
Because of scams involving R-value claims that didn’t match reality, the U.S. Federal Trade Commission (FTC) devised the R-value Rule to protect buyers of insulating products. In fact, in 2013 the FTC handed down its largest fine ever ($350,000) to a company claiming that its paint had an R-value of 100.
So, the R-value Rule requires testing insulation using one of four American Society of Test Methods (ASTM) standards. The basic requirement is that the mean temperature must be 75° F (24° C) with a temperature difference of 50° F (28° C) across the insulation.
According to Building Science Corporation, most R-value testing is done with a temperature of 50° F (10° C) on the cold side and 100° F (38° C) on the hot side.
The Lowdown on R-value
The main point here is that R-value isn’t some constant number for a given material, and installation isn’t the only factor that affects it. As you can see above, temperature has a significant effect as well.
The team at The Green Cocoon knows that the performance of the insulation is affected by how well it is installed. Energystar.gov has developed guidelines for grading the quality of installation. Moreover, they’ve developed a table that shows what levels of insulation are cost-effective for different climates and locations in the home.
Improperly installed insulation loses its R-value. For example, fiberglass can lose up to 50 percent of its prescribed R-value when compressed. When you compress fiberglass batt insulation, the R-value per inch goes up, but the overall R-value goes down because you have less inches or thickness of insulation.
Fear not, closed cell spray foam is the only insulation material that has an almost constant R-value. The reason is because you cannot pass air through it or compress it.
Contact us to find out more about R-value or for a free quote.
 Building Performance Institute (April 4, 2017). What Does R-Value Mean? Retrieved from bpihomeowner.org.
 FTC.gov (January 31, 2013). FTC Action Leads to Court Order: Home Insulation Marketer to Pay $350,000. Retrieved from ftc.gov.
 Electronic Code of Federal Regulations (March 31, 2020). R-value Rule. Retrieved from ecfr.gov.
 Building Science Corporation (April 12, 2013). Info-502: Temperature Dependence of R-values in Polyisocyanurate Roof Insulation. Retrieved from buildingscience.com.
 Energy.gov. Recommend Home Insulation R-Values. Retrieved from energy.gov.
 Insulation Institute. The Facts About Compressing Fiber Glass Insulation. Retrieved from insulationinstitute.org.