With its focus on reduced energy consumption, contemporary housing construction requires a highly insulated and airtight building envelope with as few thermal bridges as possible.Windows must be carefully designed, as thermal bridges can lead to surface condensation or mold growth, even if the window has an U-factor of 1 W/(m² x K) or lower.

This paper describes the development of modern, energy efficient Danish windows with reduced thermal bridges. It focuses on materials, geometry, and sealing of window panes based on a literature review. Examples of modern windows are presented. Experience with the minimum acceptable surface temperature regarding surface condensation or mold growth, implemented in the Danish Building Regulations in 2010 (Danish Enterprise and Construction Authority 2010), and the calculation method for this temperature based on international standards is discussed.

The introduction of the minimum acceptable surface temperature has been an important driver for the development of new window solutions in Denmark, increasing the inner-surface temperature at the sealing of window panes. However, it will not stop complaints fromconsumers, as this temperature is calculated under standardized conditions. Increasing requirements for airtightness increases the importance of sufficient ventilation in order to prevent problems with condensation or mold growth.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings XII, December 2013