R-value, or resistance value, measures how well insulation handles energy loss.
R-values are measured by inch of thickness.
Each climate zone in the U.S. has its own recommended R-value.
Common areas to insulate include attics, floors, walls, crawlspaces, garages, and ceilings.
Insulation is every homeowner's best friend when it comes to maintaining an efficient home. If your attic or walls need more insulation, it’s only a matter of time before you encounter a little letter “R” followed by a combination of numbers. What is R-value, and how does it pertain to insulation? The R-value assigned to each type of insulation is an important qualifier you should understand before choosing some for your next project.
Understanding Insulation and R-Value
R-value stands for resistance-value, but what exactly are we “resisting?” For insulation purposes, R-value refers to how well insulation keeps hot air in or out of a home (or resists hot air). The higher the R-value, the better the insulation is at reducing energy loss. Depending on the season, you can use R-value to predict how well your insulation will keep you nice and toasty or cool as an ice cube.
R-values are measured by inch of thickness. Typically, the higher the R-value per inch of thickness, the higher the cost of insulation.
Types of Insulation
There are four main types of home insulation, all of which have different R-values. These types include:
Fiberglass: 3.5–3.7 R-value per inch
Spray foam (open and closed): 3.5–7 R-value per inch
Loose-fill or blown-in cellulose: 3.5–3.7 R-value per inch
Mineral wool: 3.0–3.3 R-value per inch
R-Values and Climate Zones
How high you need your R-value to reach depends mostly on your climate zone. U.S. zones range from one to eight, with one needing the lowest R-value for energy efficiency and eight needing the highest. Generally, the majority of the United States will fall into zones two through six, though there are a few exceptions to the rule.
For instance, the very southern tip of Florida and Hawaii will fall into zone one. Most of Alaska will fall into zone seven but veer into zone eight as they move north.
If your home needs new insulation or could benefit from an upgrade, a local insulation company will calculate the total R-value needed in your walls, attics, floors, and possible crawlspaces if you have one. This total R-value is not the listed R-value, but the total amount of insulation your room needs to reach the recommended level.
For example, say you live in zone four, which typically recommends an R-value of around R38 to R60 for attic insulation. Rather than finding insulation with an R-value of R38 per inch of thickness, you simply need to have enough inches of insulation to equal the recommended R-value. If your attic has, say, 12 inches of room for insulation, you’ll need to source insulation with an R-value from R3.2 to R5, equating to a total R-value of R38.4 to R60.
The table below breaks down the general R-value recommendations based on climate zones.
Choosing Where to Insulate and Which Type to Use
Ideally, you’ll want to have insulation in all of the areas listed above and in your garage or ceiling (for those with two-story homes). A local pro can recommend the best type of insulation for your home if your existing materials aren’t getting the job done.
You’re not limited to only using one type of insulation either. In fact, most homeowners looking to replace the insulation of their homes opt to stack the insulation for better climate control and energy efficiency.
It’s not uncommon to reinforce fiberglass insulation throughout the walls of your attic with spray foam insulation that can help fill in remaining gaps and increase your overall R-value. Just make sure to stay within recommended ranges as to not overpay for insulation. Again, a local insulation company will work with your climate and suggest a course of action that’s best for your home.