Limits of U Value
U value measures insulation’s ability to limit conductive heat flow, the lower the U value the better (heat that is transferred through it). But the primary method of heat transfer is not conductive heat flow — it’s air leakage (convection), which can account for up to 40% of a building’s energy loss.
In addition, U value only does so much to prevent even conductive heat flow. Beyond a certain point, increasing insulation to reduce U value makes very little difference, if any. In fact, the cost of reducing U 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 reduce U value, but rather to combine U value with an air barrier. Elastochem spray foam insulation provides both in a single step.