R-values help homeowners decide which type of insulation material to use, and in what thickness. An R-value is a measure of a given material’s thermal resistance, or its ability to inhibit warm air movement toward colder spaces. Often, manufacturers stamp R-values on the paper side of fiberglass batting insulation. Find the printed value, and you know the R-value in the attic.
However, the R-value of loose-fill insulation or multiple layers of batting is more difficult to determine, and R-values shrink when batting settles over time. You can determine the R-value with some quick calculations.
- Wear a dust mask, gloves and a long-sleeved shirt when working with insulation. Fiberglass and other insulation materials are scratchy irritants, and you can easily inhale the tiny fibers.
- Access the attic through the pull-down ladder already installed in your home, or with a stepladder placed so you can climb through the opening. Use caution when walking in the attic space since most attics do not have a floor. You’ll support yourself by standing on the joists. A slip could result in injury and damage to the home’s ceiling drywall.
- Extend a tape measure into a joist bay — the insulated space between two joists. Push the tape all the way down until it meets resistance when it contacts the drywall.
- Read the measurement where the tape measure meets the top of the insulation.
- Determine the type of insulation material you have in the attic. According to the Oak Ridge National Laboratory, loose, light-weight yellow, pink or white is likely fiberglass; dark gray to nearly white material, often with black specks is probably rock wool; small, gray fibers or flat pieces indicate cellulose; and blankets of light-weight yellow, pink or white material (often with a paper backing facing the home’s interior) is fiberglass batting.
- Calculate the R-value of your attic insulation by multiplying the measurement you took by a factor based on the type of insulation you have in the attic. The Oak Ridge National Laboratory recommends using a factor of 2.5 for loose fiberglass; 2.8 for rock wool; 3.7 for cellulose; and 3.2 for fiberglass batting. For example, if your home has cellulose insulation at a depth of 8 inches between the joists, the attic insulation has an R-value of 3.7 times 8, or 29.6.
You can read the original article here. The author, Robert Korpella, has been writing professionally since 2000. He is a certified Master Naturalist, regularly monitors stream water quality and is the editor of freshare.net, a site exploring the Ozarks outdoors. Korpella’s work has appeared in a variety of publications. He holds a bachelor’s degree from the University of Arkansas.