R-value measures insulation’s ability to limit conductive heat flow (heat that is transferred through it). But air leakage (convection) is just as important in controlling heat flow and it can account for up to 40% of a commercial building’s energy loss.
In addition, there is a point where adding insulation does little to limit conductive heat flow and makes very little difference to a building’s energy usage. In fact, at this point the cost of increasing R value alone can actually far outweigh the energy savings that result, meaning it will take much longer to break even.
Therefore, the best way to increase efficiency is not merely to increase R value, but rather to combine R value with an air barrier. Icynene spray foam insulation provides both in a single step.
R means resistance to heat flow. The higher the R-value, the greater the insulating power. Compare insulation R-values before you buy. There are other factors to consider. The amount of insulation you need depends mainly on the climate you live in. Also, your fuel savings from insulation will depend upon the climate, the type and size of your house, the amount of insulation already in your house, and your fuel use patterns and family size. If you buy too much insulation, it will cost you more than what you'll save on fuel. To get the marked R-value, it is essential that this insulation be installed properly.