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Understanding How Spray Foam Affects Your Home's R-Values

Insulation is an important component of any commercial or residential structure. Whether you are building a new house, putting on an addition, or spot repairing a section of wall or roofing, insulation will be a major factor in your project. Many factors will influence your insulation decisions, including your budget and local code requirements. When selecting your insulation, one of the first things you will need to decide is whether to use spray foam or traditional fiberglass blankets. To properly compare these two options, you will need to have a core understanding of R-values and how they impact your home's insulation

R-Value Basics

Your insulation's R-value is a measure of its ability to prevent the transfer of heat. The mechanism by which this happens will differ depending on the type of insulation that you use, but R-values are always comparable. R-values work on an ascending scale, so higher R-values provide greater insulation. Note that while R-values measure resistance to thermal conductivity, higher R-value insulation also provides a greater insulating effect against noise. When selecting insulation for your home, it is crucial to consult a regional R-value chart to determine the proper amount of insulation for your area.

Comparing Fiberglass and Spray Foam R-Values

While R-values are always comparable, you may notice that fiberglass blankets seem to have higher R-value ratings than most spray foam. At first glance, this can make it look as though fiberglass insulation is a superior choice, but this is simply the result of the method used to describe the R-values for each type of insulation. Fiberglass insulation is sold in "blankets" with pre-set thicknesses, so a 4" thick R-13 fiberglass blanket is providing an R-value of 3.25 per inch. Since spray foam expands to fill its space, spray foam R-values are always given per inch.

Another essential factor to consider is compression. Fiberglass blankets can only provide their full R-value when uncompressed. Installing a 4" thick blanket into a 3" deep wall space will reduce the overall R-value of the insulation, further reduce the amount of insulation provided per inch. Spray foams do not compress in this way and so reliably provide their given per-inch R-value.

Total Wall R-Value

Finally, you should always consider the overall R-value of any wall or ceiling where you are installing insulation. The complications for this are complicated and best left to skilled contractors, but there are a few things to keep in mind. In addition to the adverse effects of compression on fiberglass insulation, you must also consider the ability of studs and air gaps within the walls to transmit heat. This latter issue can be a problem with closed-cell spray foam since it often cannot fill a space without gaps. Open-cell spray foam does not have this issue since it can be expanded beyond the studs and trimmed even.

If you are attempting to determine the R-value of your walls on your own, using an online R-value calculator can help. In most cases, however, it is best to leave this up to the professionals. A skilled spray foam contractor can go over your required insulation value and the best way to achieve it while staying within your budget.