A recent study performed by the Building Science Corporation (BSC) found that the insulating R-value of commonly used insulation is not constant. Its ability to resist thermal change varies depending on the outdoor temperature. The good news for New Jersey homeowners is that in most cases, the R-value rises as temperatures fall (or basically when you need insulation the most).

The R in R-value stands for resistance. Each number following the R indicates how many hours the product can resist thermal change. Insulation with an R-value of 16 theoretically can resist thermal change for 16 hours. Most people have always regarded the R-value as constant, but the BSC set up laboratory conditions with temperatures that ranged from minus-30 degrees F to 150 degrees F, and learned that…

  • At minus-30 degrees, an R-13 fiberglass batt has an R-value of 15 and at 150 degrees, it plummets to just over 11.
  • At minus-30, a sheet of R-16 expanded polystyrene (EPS) has an R-value of 17.25, and at 150 degrees, it falls to 14.75. EPS is what foam coolers are made from, along with Styrofoam cups.

Another type of insulation is polyisocyanurate (polyiso), which has an R-value of 6 per inch, compared to 3 for a fiberglass batt. However, this insulation loses some of its insulating R-value as temperatures fall. The implications for homeowners who are contemplating this product are to make sure that it’s carefully installed in attics, ceilings, or wall cavities or simply use more of it. It’s a tempting insulation to use regardless of falling R-values in cold weather because it has twice the R-value of fiberglass per inch of thickness, making it a space saver.

Another factor to consider if your home has fiberglass batts in the attic is the very hot temperatures in the attic during the summer. Installing an attic fan to use when it’s hot outdoors can reduce heat gain in the summer and lower your cooling bills.

If you have questions about the insulating R-value throughout your home, please contact us at Pipe Works Services. We’ve provided exceptional HVAC services for northern New Jersey homeowners for more than 10 years.

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