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Which R-Value Should I Use?

Whether you’re building a 20’ x 40’ shop in your backyard, or a 75’ x 200’ structure for your expanding business, you’ll have some important decisions to make regarding R-value. R-value indicates the insulation’s capacity to resist heat flow. The higher the R-value, the better the insulation’s ability to hold heat, or keep your building cool.

Each R-value rating comes in a different thickness. R-7: 2.5”, R-10: 3”, R-11: 3.5”, R-13: 4”, R-19: 6”, R-25: 8”, R-30: 9”. Insulation can be layered to achieve higher R-values. This method of layering is often referred to as a “double layer system”. Your method of installation will help determine which R-value options you will have. This can be determined by your building’s specs and whether your building is a new build or an existing structure.

If you’re constructing a new building the option to “pinch” any single layer R-value up to an R-19 (6” thickness) between the purlins/girts and the metal sheeting, is available. However, keep in mind that pinching or compressing fiberglass results in a lowered fiberglass efficiency.  If your new building has an energy efficiency code to follow, or you’d like an R-value higher than R-19, then a double layer system, stuffing the cavity with insulation and then blanketing another layer over the purlins/girts will most likely be your method of choice. For example, an R-38 is achieved by stuffing the cavity with R-25 (8” thickness) and blanketing R-13 (4” thickness) over the purlins/girts.

If you are planning to add insulation to an existing building, than the R-value will be determined by the depth of the purlins and girts. For instance, a 6” purlin will call for an R-19 (6” thickness), 8” purlins will call for an R-25 (8” thickness). Filling the purlin/girt cavity completely is important as it helps to prevent water moisture from collecting in between the metal sheeting and insulation. So now that you’re armed with a little more knowledge about selecting the right R-value for your building–it’s time to get insulating!

by, Heather Aaron