Spacers At Lawrence Berkeley National Laboratory, surface properties of shading and daylighting systems are first measured using a scanning radiometer (top), then modeled as a system (middle) to produce full bi-directional solar-optical data (bottom). Image courtesy of Lawrence Berkeley National Laboratory

Designers of commercial buildings must choose from a wide range of possible window materials and assemblies. This is an introduction to the properties and technologies that make up an energy-efficient window system.

Glass and Window Properties Primer

This is an introduction to the basic mechanisms of heat transfer and the key properties of glazing that affect energy performance: transmittance, reflectance, absorptance, and emittance.

Glass Technologies

The the commonly used energy-related properties of windows are: insulating value (U-factor), ability to control heat gain from solar radiation (SHGC and SC), and visible light transmittance (VT). Various coatings, tints, and other glass surface treatments can affect the energy properties of windows. Explore the glass technology options listed to the left.

Assembly Technologies

Glass technology is combined with a spacer system and a gas fill between the panes to produce and energy-efficient insulating glass unit (IGU). These IGUs are assembled with frame and operability options to form the complete window assembly. Explore the window assembly technology options listed to the left.

Advanced Technologies

Most of the emerging glazing technologies presented in this section are available or nearly on the market. Insulation-filled and evacuated glazings improve heat transfer by lowering U-factors. Switchable glazings, such as electrochromics, change properties dynamically to control solar heat gain, daylight, glare, and view. Building-integrated photovoltaic solar collectors involving window systems not only generate energy but also form part of the building envelope.


Facade Design Tool



Window Technologies

Case Studies

Tools & Resources