European Windows for Passive House Buildings

What is it about European windows that makes them so popular for ultra-low-energy Passive House projects? The glass is largely the same; in fact, American companies have led the development of low-e glazings. In a nutshell, it is the frames, gasketing, and hardware that separate top-quality European windows from their American counterparts. And, ironically, the testing standard used for American windows has to some extent held American windows back.

The National Fenestration Rating Council (NFRC) was established in the U.S. in 1989 to standardize the testing and reporting of window energy performance. Prior to the formation of NFRC, window manufacturers used different methods to report their performance. Consumers and specifiers couldn’t compare apples to apples. Among the most important performance metrics to be addressed by NFRC was the U-factor, the amount of heat flow through a whole window unit under certain testing conditions. U-factor is the inverse of R-value, and until NFRC came along, manufacturers most commonly reported energy performance as the center-of-glass R-value.