R-Value vs R-Values
What is R-Value?
R-Value is defined as a materials ability to resist heat flow. It’s a complex equation to state in mathematical terms, but the R-Value number is the ratio of temperature difference across an insulation material and the heat difference per unit area. So you might be asking, why compare them, aren’t they all the same? The answer is simple… NO! Yet we continually use R-value as the principle ingredient in our quest to gain energy efficiency. Spray Foam vs. Fiberglass Insulation The answer of which is better revolves around how R-Values are tested. The hot plate method essentially uses a heat element on the one side of the box and the test piece of insulation in between (insulation medium).
When the temperature on the opposite insulation reaches a pre-defined temperature, the insulation material is given an insulation value. All materials are tested the same way. The problem with testing R-Value alone is that the testing is done in laboratory conditions. When insulation is installed in homes and buildings the environment is much different. Insulation materials must deal with: pressure differences from inside and outside, mechanical ventilation, and most of all moisture.
This explains why spray foam homes are 40-50% more efficient than a typical fiberglass insulated home. The key is installed efficiency: how efficient or effective is the product when installed in real life conditions? Fiberglass’ R-value drops off dramatically once it has to deal with a variety of environmental conditions. Spray foam is not affected by mechanical ventilation, or wind, or by moisture. Therefore its R- Value remains constant, providing energy savings forever. So just how effective is your R-value?
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