WHAT DOES THE DEFINITION OF R-VALUE INCLUDE? IS R-VALUE THE ONLY THING I NEED TO CONSIDER WHEN WEIGHING THE TRUE PERFORMANCE OF INSULATION?
The truth about R-Value
R-value only measures how well insulation resists heat movement through the insulation material (called conductive heat flow). The advertised R-value of conventional insulation, usually printed on its packaging, is determined by multiplying its thickness (in inches) by its R-value/per inch.
R-Value per inch (3.6) x 3.5 inches of insulation = R-12.6. (laboratory R-value)
R-value is a popular way of comparing insulation, but it only tells part of the story of how well insulation will work in your home. Here are three reasons why:
R-value doesn't measure air leakage control.
R-value only measures energy moving in and out of your home through the insulation material (conduction). But energy (in the form of heat) can move in and out of your home in three ways:
Convection Through Air Flow (random air leaks) Air leakage can cause up to half your house’s energy loss
Conduction Through materials as a result of temperature differences across materials (walls, ceilings, insulation)
Radiation In waves (i.e. from sun through windows)
Building codes in your area usually set a minimal acceptable level of R-value for areas in a home. But if insulation doesn't help stop random air leakage, it's not helping you control the source of up to half of the energy lost by your home (convection).
To make the best insulation investment, consider a product offering the best of both worlds: an ideal level of R-value and control of random air leakage.
R-value is based on specific laboratory conditions.
In real homes, the R-value advertised can be diminished if insulation gets wet or if it's installed improperly (cut improperly or compressed into wall cavities).
Surprise! More or thicker insulation and higher R-values are not always better.
Most (93%) conductive heat flow (heat flow through a solid) is already controlled by R-12 insulation. That means doubling R-value (from R-12 to R-24 for example) won't double your savings. The real R-value of insulation when installed can be as little as 50% of the R-value listed on the package. (Source: California Energy Commission study)
Why Insulation is Not Enough
The fact is you can't achieve the kind of energy efficiency you want by simply adding insulation. You need an air barrier to stop uncontrolled air leakage. The United States Department of Energy reports that over 30-40 percent of the cost of heating and cooling a home is lost to uncontrolled air leakage.
In addition to costing money, air leakage also contributes to problems with moisture, mold growth, thermal comfort, noise, dust and pollutants, as well as premature structural deterioration and ice damming.
Glass fiber insulation will not stop air leakage no matter how much you install. In fact, if you visit older homes you might see dirty, discolored glass fiber—a telltale sign of air movement, as it collects dirt like a filter.
With uncontrolled air leakage, the furnace and air conditioner have to work harder to maintain the indoor environment. Spray Foam's combination insulation and air barrier eliminates uncontrolled air leakage by contributing to a monolithic, air impermeable building envelope system. This allows the heating and cooling equipment to do its job uncompromised by having to make up for the air it is conditioning leaving the house.
Increasing the operating efficiency of the heating and cooling equipment reduces energy consumption and therefore energy costs. The inclusion of an effective air barrier system may allow the equipment to be downsized- in some cases by a substantial amount.