Simply put, R-value is a measurement of how insulating a building material is, protecting one side from the heat or cold on the other side. A higher R-value means that a material insulates better than one with a lower value.
In order to get an idea of what these values are, here are a few examples of common building materials and their R-values:
- 1/2″ drywall – 0.45
- 1/2″ plywood – 0.62
- 4″ wide brick – 0.80
- 1″ of concrete – 0.52
- Single pane of glass – 0.91
- 2″ insulated metal door – 2.00
- Dual Pane Low E glass – 2.5
R-Value of Building Insulation
Building insulation has different R-values depending on the type of material being used and the thickness. Different materials are used in different areas of green building, and they are designed to be used in different types of construction.
Here are a few common types of building insulation:
Fiberglass – Made of blown glass threads that are either matted together into batts or distributed loosely, this is the most common material used in residential construction today. The fiberglass “batts” are either stuffed into the spaces between the studs in the exterior walls of a building, or they may be laid down on the bottom of an attic space. Other forms of insulation, such as loose-fill or boards, are used in other locations, such as a basement or crawl space. Fiberglass batts come in a wide range of R-values, most commonly from R-11 to R-38.
Foam – Spray foam insulation is made by mixing two chemicals (isocyanate and polyol resin, if you are interested) that react and cause the foam to expand to fill the space it is placed in. It can be shot into spaces through small access holes, making installation in retrofit projects easier than standard batts. There are two types of spray foam – open and closed cell – with closed-cell being the densest and therefore has a higher R-value. Foam averages R-5 to R-6 per inch, compared to R-2 to R-4 per inch of fiberglass.
Recycled denim – Blue jeans and other denim products are shredded and the cotton fibers are woven together to form batts, similar to standard fiberglass insulation. The denim used to produce this insulation is post-consumer, so it removes products from the waste stream and repurposes them. Denim batts provide slightly better R-values than similar thicknesses of fiberglass.
What Does This Have To Do Windows?
So, why is all this important? A typical double-pane window achieves an R-2.0. Better windows have higher R-values and low U-factors. Higher numbers mean more insulation.