The article "Trends in window & facade construction" in the August 2009 number of Window Technologies shows there is a need to increase energy efficiency in existing buildings by using innovative technologies.

Studies performed by the German Energy Agency (dena) indicate that the amount of energy used to heat buildings can be reduced by up to 85% - simply by replacing existing energy-intensive windows with modern equivalents.

The U-value requirements for windows were therefore tightened up in the new EnEV regulations introduced in October 2009. The U-value has been reduced from 1.7 to 1.30 W/(m2K)