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Insulation R-Value Explained

If you’ve read anything about insulation or looked into an insulation project for your home, then you’ve no doubt come across the ubiquitous yet hardly explained term “R-value.” Denoted as R- followed by a number, it’s an important figure having to do with the proper kind and amount of insulation needed for a home to be up to recommended standards. But what does it mean?


Technically, an R-value is a more general unit of measurement used in the construction industry to describe a material’s resistance to heat transfer. There’s a bit more to it, but since its technical definition is something best left to a physics classroom, we’ll just give you the practical stuff you need to know.

Simply put, a piece of insulation’s R-value is a rating of how well that material can insulate. An inch of insulation with a higher R-value will be more effective than an inch of insulation with a lower R-value. But really, this only tells you how many inches of a given insulation you need, as you can stack as many inches as it takes for you to get to your target R-value—it adds up.

Speaking of those target values, below is an overview of how much insulation is needed for the various parts of a home:

The Attic

Being the highest point in the house, the attic takes on the role of a sort of barrier between the hot sun and the rest of the house. Because of this, it’s the most important room when it comes to insulation, and it needs a higher R-value than any other part of the house. But the exact amount depends on whether you live in a warm or cold climate.

Attics in a cold climate are recommended to have at least an R-49, while the bar for warmer climates is set at R-38. That would be roughly equivalent to 16 inches and 12 inches of fiberglass, respectively.

The Floors

Unlike attics, the R-value isn’t the only important consideration when placing insulation under your floors. Venting and moisture can become problems, so you typically don’t want as much insulation as is needed in the attic: R-25 in cold climates and R-11 in warmer climates is what’s recommended by the U.S. Department of Energy.

The Walls

Because wall studs are only so thick, the R-value of wall insulation is really limited to the amount of material you can fit in your walls. Then, it really comes down to what type of material you can get the most insulation from in a tight space—Fiberglass might only be able to get you a maximum of R-15 in the walls, while sprayed foam insulation can get an R-rating of up to R-28 in the same wall cavity. On the topic of materials, bellow you can find a comparison of a few common types of insulation available to DIY or from the pros:

DIY-Friendly Materials

The most common type of insulation material available for DIY-ers is fiberglass. An inch of thickness of loose fiberglass typically won’t exceed an R-value of 3, but fiberglass batts can go as high as 3.8. There are a variety of of other materials available such as Cellulose, Stone Wool, and Cotton, but they all achieve similar results when compared to fiberglass.

If you take on one of these materials in a DIY insulation project, be sure to wear gloves, goggles, long sleeve clothing, and a respirator or mask. And try not to work in the attic during the hottest months of summer!


The real efficiency is in foams—Polyicynene, Phenolic, Polyisocyanurate, and Polyurethane. These are chemicals that turn into a foam when sprayed, and some of them can reach R-values of up to 8.0 per inch! While they are the most effective, under no circumstances should you attempt to DIY these materials. Always hire a pro if you’re looking for this type of insulation.

Remember to give us a call if you have any questions about insulation; we would be more than happy to help!