Insulation Questions: What is R-Value?

If you have ever asked about or research upgrading the insulation in your home, you have most likely heard someone mention R-value. You can probably guess the basic parameters of R-value — higher is better. But what does it actually mean? What does the R stand for? Why are the values different for different insulation materials? In short, what is R-value?

We’re here to help. Here is a primer on the basics of R-value and what it means for insulating your home. Call us now at 425-482-2121 for a free estimate, and improve your insulation today!

What is R-Value? The Basics

what is r-value

R-value is short for resistance value. When looking at insulation, R-value measures how effective a material is at insulating your home. It is a measure of how much resistance the material has against heat flow. Counter to what you may believe, insulation does not just keep outside temperatures from getting in your house. Insulation stops heat flow in both directions. So in winter, your insulation keeps your indoor heat from flowing out, and in summer, it keeps hot air from getting in. Insulation, and R-value, is all about heat conductivity.

R-value is not only used to evaluate insulation — it’s also used to measure the insulating effectiveness of all construction materials, including windows, walls, ceilings and roofs. And R-value is additive, meaning if you add more material, its R-value increases. Due to some very complicated math, however, it’s not always straight addition — the thicker the insulation, the lower its R-value per inch. If a one-inch barrier of fiberglass batt insulation is R-10, a three-inch barrier of the same material might not be R-30.

Thankfully, U.S. law requires manufacturers to print the total R-value of a product on its label. So you’ll always know exactly how much heat flow resistance you’re getting when you buy insulation.

TL;DR — higher R-value is better.

Different Materials, Different R-Values

There are multiple types of insulating material you can choose, and each one has its pluses and minuses. Here are some of the most common (NOTE: although manufacturers can’t promote the R-value per inch of their products, that’s precisely what I AM going to do, for comparison’s sake):

  • Cellulose: With an R-value around R-3.2 to 3.9 per inch of thickness, cellulose is one of the more inefficient insulating products available. However, it’s inexpensive and easy to install, which makes it popular for insulating already-finished walls, ceiling and floors. You can blow in a deep layer of cellulose, without having to tear out any walls or floors, and still have a fairly well-insulated space.
  • Fiberglass: This is the most common material used in insulation, with R-values around R-3.1 to 4.3 per inch of thickness. That may not seem much better than cellulose, but fiberglass batting comes in thick sheets that can be cut to precise measurements to fit between joists, studs and rafters. This is the pink stuff you’re used to seeing.
  • Spray foam: Although there are two types of spray foam insulation, at Eastside we only use closed-cell foam, which is about twice as effective as open-cell. Closed-cell spray foam has an R-value around R-6.0 to 6.5 per inch of thickness, making it far more effective than fiberglass or cellulose. As such, it’s also more expensive. But if you need the most efficient insulation possible in the least amount of space, spray foam is the way to go.

R-Value Lowers Over Time

As your insulation ages, its R-value decreases. This is especially true of cellulose and fiberglass, which settles and depresses over time to become thinner than when installed. (And as we discussed, less thickness = lower R-value).

If insulation is undamaged, it has a very long shelf life. Spray foam can last up to 80 years, while cellulose and other blown-in materials (like rock wool) can last a century. This is under best-case scenarios, however, and the R-value of the insulation will steadily decrease over that time. And if your insulation is damaged by water, rodents or other means, it should be replaced ASAP.

Hopefully, this guide has helped you understand your insulation needs and can help you in planning your project. Call Eastside Insulation now at 425-482-2121 for a free estimate, and let our expert professionals lead the way!

You May Also Like