According to the Energy.gov site, R-value is defined as:
“A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties.”
If you’re like most people, that hasn’t really answered your question.
In simple terms, R-value is a measure of heat resistance – specifically, resistance to conductive heat, or heat that’s being transferred through a material. For insulation, the higher the R-value number, the more the insulation will prevent a loss of heat through conduction. High R-value means high insulating abilities and less heat flow.
In the USA, the Federal Trade Commission has a rule regarding the standardized use of R-value. In order to make things easier for people buying insulation, they have a “per inch thickness” R-value rule that makes it far easier to compare the effectiveness of an insulation product.
They also have many other rules in regards to how you can advertise all these things, see here for the full regulations.
R-Value and Spray Foam Insulation
If you’re using one of our closed-cell spray foam insulation kits, you’re going to be getting an R-value of around 6.8 per inch thickness. On its own, this number stands out against other insulations that can be purchased for less.
With all the focus on R-value though, it can be easy to miss the fact that there’s more to choosing an insulation type than R-value alone. Spray foam insulation protects from heat loss in three different ways and R-value is only one of them.
These are R-value (conduction), convection, and radiation.
Convection is heat loss or gain via air currents, so to avoid this you can fill up all the gaps and cavities in your home. SPF does this for you as it expands, so immediately increases your levels of retained heat. It’s also dense enough that high winds won’t work their way through it like normal fiberglass insulation.
Radiant heat barriers are also something that spray foam insulation has, and just another way that it insulates against heat loss. Radiant heat is based around energy being emitted through light and reflection.
How Much Spray Foam Insulation Do You Need?
Insulation needs vary from state to state, but it’s better to have too much insulation than too little. Warmer climates require less insulation and colder climates require more. The higher the R-value of your insulation, the higher the comfort level of your home — not to mention the lower your heating and cooling bills will be.
It’s important to check local building codes to make sure that you’re using enough insulation. And be sure to check the Recommended Home Insulation R-Values from energystar.gov.