How insulation R-values can affect your bottom line
Jeffrey Anderson | Improvement Center Columnist | July 29, 2013
As a homeowner, you've probably heard the term "R-value" many times -- especially with the growing trend toward making houses more eco-friendly in recent years. But what exactly is R-value and how do you know if your home has enough? Does the term refer only to insulation or are other materials involved?
Knowing the answers to these questions may help you decide what upgrades might be most beneficial to your home and budget. It could also play a part in material selection for any remodeling or room addition project you may have planned.
One of the basic laws of physics is that heat gradually moves toward cooler areas until any temperature difference is eliminated. This theory of conduction plays a big part in how much energy is used to heat and cool your home. In the winter, the warm interior air you're paying to heat naturally moves toward unconditioned, cooler parts of your home such as the attic, basement, or garage. The reverse is true during the summer months when hot outside air wants to get inside your cooler, air-conditioned house.
The U.S. Department of Energy defines R-value as a measurement of "an insulating material's resistance to conductive heat flow." R-value can also be thought of as a material's "thermal resistance." In layman's language, R-value is a measurement of how well a material does at preventing the loss of your home's warm air in the winter and keeping hot air outside during the summer. Higher R-values are considered to be more effective in accomplishing these tasks.
R-value and your building envelope
So what parts of your home should be of concern when it comes to R-value? Basically, they are the assemblies that form the envelope or barrier that separates the conditioned parts of your home from unconditioned areas and the outside. These might include the following:
- Exterior walls
- Roof system
- Basement walls or ceiling
- Crawlspace walls or ceiling
The total R-values of each of these barriers is figured by adding up the individual R-values of all the insulating materials used to make up the assembly. When calculating the thermal resistance of an exterior wall, for example, the R-values of the siding, intermediate sheathing, insulation, and interior sheetrock would be added together. If you have a finished attic, the values of the insulation batts between the rafters, the sheathing, and the roofing materials would make up the assembly's total thermal resistance.
Insulation: the ultimate R-value protection for homes
While many materials have an R-value rating, without a doubt the various types of insulation provide the most thermal protection for your home. Consider these R-values of a few common materials used in the construction of houses:
- 1/2-inch sheetrock -- .45
- standard vinyl siding -- .61
- ½-inch roof sheathing -- .62
- insulated vinyl siding -- 2.7
- ½-inch insulation-board intermediate siding -- 3.3
- 3.5-inch batt insulation -- 13
- 3-inch closed foam spray insulation -- 19
- 6-inch batt insulation -- 19
- 2.3-inches of blown-in insulation -- 30
These thermal resistance ratings may vary by product and manufacturer, but it's easy to see that if you want to beef up the R-values of your home's outer envelope, adding insulation might be a good place to begin. However, don't overlook the thermal resistance that some other materials such as insulated vinyl siding can provide -- even a small R-value increase can contribute toward lower heating and cooling bills and may be all that's needed on a newer home to reach current guidelines. However, on an older home that might have little or no insulation in its exterior walls, installing spray foam or blown-in insulation may be the best solution to achieve today's thermal-resistance recommendations.
R-value: How much do you need?
So now that you know what R-value is and how it can affect your home, how much do you need in your outer envelope? Andrew Haak of Insulwise Energy & Comfort Solutions in Pittsburgh, Pa., suggests that the Energy Star website might be the best place to start. He feels that the site is very user-friendly and makes it easy for homeowners to research the recommended R-values for their particular region.
The 2012 International Energy Code Council (IECC) guidelines also provide a little more detail on ways to reach the recommended R-values. The latest IECC codes from 2012 say to use R-20 for Climate Zone 4 wood frame outer walls. To achieve the new recommended value, you can use either an R-20 spray foam or batt insulation in the walls' inner cavity or combine an R-13 insulation material and an R-5 exterior sheathing board. Make sure you know the correct climate zone for your home's location as thermal-resistance requirements can differ quite a bit between places, for example, like Montana and Florida.
Haak also states that while both Energy Star and IECC guidelines may be good introductions to recommended R-values, an energy audit is often handy in determining where your home's insulation might be lacking. A quick call to your local building inspection department can be a good way to find out the recommended R-values for the various barriers in your home's outer envelope as well.
A better understanding of R-values can help you make your home more energy efficient, and that could lower your monthly utility costs.