Understanding R-value Of Insulation

By Author: Mark Munns
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When shopping for insulation products, whether spray foam, rolled, or loose insulation, you will likely encounter a bunch of numbers associated with a term called R-value applied to the different products. If you've been wondering what all those different R-value numbers mean, there is a simple explanation.

When it comes to insulation, the effectiveness of each type is measured by R-value. R-value simply refers to the material's thermal resistance, or rather the insulation's ability to resist heat flow. The R-value is simply the thermal resistance value designated for each type of insulation and the higher the R-value, the more effective the insulation is at reducing heat flow.

To gain a better understanding of why a higher R-value is more effective than a lower value, you need to understand how insulation works. To effectively reduce energy use and costs, providing a home with insulation to resist heat flow is essential. Heat tends to flow naturally from warm spaces to cool ones. Thus, when you're heating your home in the winter, the heated air is naturally going to flow to the outside, typically through your ...
... roof and windows. By providing a resistance to the natural heat flow, you are keeping the heat in your home longer. Conversely, in the summer months, the purpose of insulation is to keep the heat outside the home from flowing into the cooler space inside the home.

The major components that make up the R-value of insulation are the type of material as well as the density and thickness of the material. The actual R-value of the product can change based on how and where the product is installed. For example, if you compress rolled insulation, you are effectively altering the thickness and consequently altering the actual R-value. If certain materials, such as wall studs or ceiling joists, are not covered with insulation then a thermal bridging occurs and the actual R-value is reduced.

Residential insulation products contain labels indicating the R-value. This information can be found on a label that also has information regarding safety and fire hazards. Other pertinent information should be clearly visible as well, such as how much of the product should be applied to a given space and at what thickness or volume. While the information on insulation labels, including the R-value, is important when choosing an insulation product, there are other things to consider as well.

Though a high R-value is important, just how high depends on the climate in which your home is located. Houses in warmer climates can obviously be effectively insulated with a lower R-value product than houses in cold climates. Other factors to consider are the construction type of the home, the type of heating and cooling system installed, and the condition of any existing insulation. Over time, all insulation will deteriorate, diminishing its value.

The U.S. Department of Energy provides information on the R-value of a variety of insulation types. Their estimates show that rolled batting 3.5 inches thick has an average R-Value of 11 but that spray foam insulation can actually double the R-value of batting, due to its ability to fill even the smallest cracks. In some spaces and under certain circumstances, it may actually make sense to install two or more different types of products to achieve maximum effectiveness.

While the actual science behind the testing and rating of insulation products can be quite complicated, the essential thing for homeowners to know is that they want to purchase an insulation product with at least the minimum R-value recommended for their area. Recommendations for different areas can also be found through the U.S. Department of Energy and other sources.

Before making a final purchase, compare products of adequate R-value to also determine which products will help reduce moisture flow, adequately insulate the area in question, and best seal off cracks and drafts. By normal estimates, homeowners can save an average of 30 percent on their energy costs by sealing off air leaks and achieving the proper level of insulation for their home's conditions. Over the course of just two heating and cooling seasons, this amount of energy savings can really add up and make the initial cost and effort more than worthwhile.
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