Sustainability · Defined
U-factor
A measure of heat transfer through a material or assembly; lower values indicate less heat transfer for the same basis.
Why it matters
A whole-window value is not identical to a center-of-glass value. Verify which assembly and units the rating describes before comparing products.
In practice
A project example
Two glazing proposals appear similar until one is found to quote glass-only performance rather than the complete window.
General educational guidance from KOW Building Consultants. Examples are illustrative, not project records. The applicable contract, standard, program, and jurisdiction control the requirements for a specific assignment.