Home Insulation R-Values: More Variable Than You Might Think – Sobieski Services | DE, NJ, PA, MD

Home Insulation R-Values: More Variable Than You Might Think

When a construction worker or home energy rater installs new insulation, you expect it to deliver the R-value printed on the packaging. However, home-insulation R-values are more variable then you might think. Here’s a look at exactly what R-value means and the factors that affect insulation’s real-world effectiveness.

What Is R-Value?

R-value is an efficiency rating for insulation. It refers to the insulation’s thermal resistance, or its ability to prevent heat from passing through it. The R-value of installed insulation varies based on material, density and thickness. Sometimes, R-value indicates how much thermal resistance the insulation provides per inch. Of course, the number printed on the packaging is merely the nominal R-value. Other factors in the real world impact how well the insulation lives up to its efficiency rating. Here’s a look at two primary factors that cause R-values to fluctuate.


If you install fiberglass batt insulation into a space that’s smaller than recommended, you are forced to compress the insulation. This decreases home-insulation R-values by minimizing the air pockets within the product that contribute to its thermal resistance.


A variety of insulation types – fiberglass batts, expanded polystyrene (EPS) and extruded polystyrene (XPS), to name a few – improve when the temperature drops outside. Above 60 degrees F, these insulation types perform below their nominal R-values, but as the temperature drops, their efficiency rises. However, temperature has the opposite effect on one popular type of insulation called polyisocyanurate, often simply called polyiso. This insulation decreases in R-value as it gets colder outside. This is relevant for cold-climate dwellers, such as those in the Mid-Atlantic region. Solutions for this problem include using more polyiso, covering it with another type of insulation to keep it warmer, or counting on exterior insulation instead of cavity insulation to meet your requirements. With these considerations in mind, you’re better prepared to accomplish higher home-insulation R-values.

To learn more, please contact us at Sobieski Services. Our goal is to help educate our customers in Delaware, Pennsylvania, Maryland and New Jersey about energy and home comfort issues (specific to HVAC & plumbing systems).

Image Credit: Pink Sherbet Photography

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