What does R Value Mean in Insulation?

No matter where you live, whether it’s in Florida or Alaska, your home will be the most comfortable if you have the right amount of insulation. Having the proper amount of insulation for your area will also help your home be more energy efficient.

Insulation is used to reduce the flow of heat so you can keep heat inside the home in winter and outside the home in summer. This has the added benefit of reducing the amount of heating and cooling you’ll need to do to your home, saving you money on the cost of utilities. So how do you know how much insulation you need?

The Meaning of R-Value

The heat resistance of insulation is measured by its R-value. The R stands for resistance to heat flow. R-value is universal across all insulation products, so the measurement will mean the same thing no matter who sells or manufactures the insulation. R-value is even consistent across different types of insulation.

Nearly all insulation products have to report R-value, with the exception of pipe and duct insulation, so it’s easy to learn the R-value of what you’re buying.

What Are the Different Values?

The higher the number, the better the insulation. The lower the number, the less resistance the insulation provides to heat. Adding more insulation increases the R-value of your home’s insulation.

What R-Value Should I Have?

What number you need depends on where you live as well as the type of home you own. The country is divided into different zones based on temperature and weather, so you should purchase insulation with an R-value appropriate for that zone. Each zone has a range of appropriate R-values, though, so you should also pay attention to what insulation the walls of your home may already be providing and what materials your home is made out of.

Zone You Live in

The lower the zone number, the warmer the zone is and the lower the required R-value for adequate insulation in that zone. The lower zones tend to be further south while higher-numbered zones are to the north. For example, Zone 1 includes Hawaii, Guam, the U.S. Virgin Islands, Puerto Rico, and the southernmost tip of Florida. Zone 7 includes parts of Montana, Minnesota, Wisconsin, Michigan, Maine, some small sections of Wyoming and Colorado, and almost all of Alaska. Zone 8 is made up of Alaska’s northernmost boroughs. There are a few exceptions, such as a Zone 6 area in California and other pockets of higher-numbered zones that are south of lower-numbered zones.

Zones aren’t calculated by location but by weather, temperature, winds, and more. Zones that may seem out of place experience weather that justifies their presence in the zone they’re in. Before purchasing any insulation, it’s important to verify what zone you’re in so you’re buying enough insulation.

If you’re insulating an uninsulated attic, for example, people living in Zone 1 should purchase insulation with an R-value between R30 and R49 while someone living in Zone 5 should buy between R49 and R60. The exact numbers will depend on what insulation you already have and the type of home you live in. To find out exactly what you need, you should consult with your insulation contractor.

Type of House

Some factors to look at that can affect the R-value needed by your home are:

• Does it have a basement or is it built on a slab?
• Is it a multistory home or single story?
• Are there cathedral ceilings?

Anything that creates more locations where cold or wind could get in (such as more stories), would increase the R-value needed to thoroughly insulate your home. Some parts of your home may be in more need of thicker insulation than other parts. Having a professional to do a walkthrough of your home can help you assess where in your house you may be losing more energy and heat.

Type of Heating and Cooling System

How you heat or cool your house does affect how much insulation you’ll need as well. If you have a furnace versus a central heating or air conditioning system can play a role in your home’s insulation needs. You may be able to get more information from your utility company.

What Factors Determine R-Value?

While R-value itself may be universal, there are several factors that go into determining R-value. While more insulation increases the R-value of what’s in your home, the base R-value of insulation when you purchase it depends on the type of insulation, plus its thickness and density.

Insulation Type

Fiberglass batting, foam board, and cellulose paper fiber are the most common types of insulation. Foam board tends to carry a higher R-value, but because of this is more expensive than the other types of insulation.

Thickness and Density

The thicker the insulation, the higher the R-value of that particular insulation. Denser insulation also carries a higher R-value. The highest R-values would be both thicker and denser.

How Can I Tell What R-Value My Insulation Has?

If you know the type of insulation you have in your home, you can calculate the R-value based on how many inches of insulation you have. Theses insulation types have the following R-values per inch:

• Sprayed foam: 3.6 to 8.2
• Loose rock wool: 2.2 to 3.3
• Blown cellulose: 3.1 to 3.8
• Batts of fiberglass: 2.9 to 3.8
• Blown fiberglass: 2.2 to 2.9

From there, multiply the R-value of an inch by the total number of inches of insulation that you have to know the approximate total R-value. A professional could help you calculate more accurately.

How Can I Increase My R-Value?

To increase your insulation’s R-value, just add more insulation. Alternatively, you could replace it with a thicker or more dense insulation if you live in a cold climate and need a higher R-value than what you currently have room for.

Is R-Value Important in Energy Efficiency?

R-value is very important for energy efficiency in both heating and cooling. The R-value of insulation reflects its ability to resist heat, both going out of your house and coming into your home. The higher the R-value, the more efficient your home will be because it won’t require as much heating or cooling, saving you money on the cost of utilities.

What Other Factors Affect Efficiency?

Other than conduction, which is the same as R-value, the other factors that can affect the efficiency of your insulation are compression, air movement, and moisture. These things can decrease the insulation’s efficiency by eliminating features that add to the insulation or by increasing its conduction of heat.