What is U-Value

Our last Blog we explained R-value, windows also can have a U-value.

U-Value is the measurement of the rate of heat loss through a material.  Which means that in all aspects of home design one should strive for the lowest U Values possible because the lower the U Value, the less heat will be needlessly escaping. It is the measure of a window's ability to reduce heat loss during indirect radiation exposure; such as during the winter months in moderating climates.Lower U-values translate into less indirect heat lost from the interior of the home resulting in lower heating costs.

U-value is the inverse of R-value (a more common term used in the insulation business). To find a correlating R-value from a given U-value, simply divide the number 1 by the U-value. Lower U-values correlate to higher R-values. For example: 1 divided by a .50 U-value gives us an R-value of 2.00.

Lower U-values are important because many municipalities are adopting the 2006 version of the International Residential Code (IRC 06 for short). This code mandates all energy efficient window and exterior door units with IG to carry a minimum U-Value of .40, translating to an R-value of 2.5.

This may sound like a low insulating value but even the finest energy efficient windows today carry U-values hovering in the .22 through .30 ranges; thus correlating to R-values of 4.55 through 3.33.

And given the fact most exterior wall cavities are a minimum R-13 (with standard 2 x 4 framing) to R-19 (with 2 x 6 framing), the most energy efficient windows are 3 to 4 times less efficient than the wall they're installed in; thus the significance to upgrade building codes with regard to window glazing applications.

So, even with the large disparity between the wall vs. window insulating factor, improving U-values greatly increases the energy efficiency of the home.