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Secondary Window Glazing Systems

An energy-saving window attachment

Secondary glazing systems (SGS) are designed for use in existing commercial office, historic, educational, and government buildings with inefficient windows. SGS are window attachments that attach to the interior of an existing window, creating a insulating barrier. The SGS target market are low-performing windows, particularly single-glazed, in existing buildings built between 1945 and 1990. For these buildings, SGS is approximately half the cost of replacement and may be installed as a stand-alone energy efficiency measure or as part of a deeper energy retrofit. 

According to the U.S. Department of Energy, 25% to 35% of energy wasted in buildings today is due to inefficient windows, adding up to 10% of total carbon emissions in the U.S. annually.

Benefits of Secondary Window Glazing

  • Thermal insulation
  • Sound and noise insulation
  • Enhanced security
  • Reduced condensation and air infiltration
  • Less cost than replacement

How Secondary Window Glazing Works

The illustration to the left demonstrates how the secondary glazing system works with your existing window to create an insulating barrier. By affixing to an existing window frame, this window attachment offers a relatively easy installation when compared to full window replacement.

*Drawing is for illustration purposes only and does not represent the sizing or depth of the system or frame for all manufacturers' products. Check with manufacturer for exact measurements and specifications.

SGS: Thermal, Moisture, and Solar Performance Analysis and Validation

The Northwest Energy Efficiency Alliance (NEEA) contracted with the Ernest Orlando Lawrence Berkeley National Laboratory to conduct a study to analyze and validate the thermal, moisture, and solar performance of SGS. To learn more about SGS performance, you can read the report at neea.org.

Read the report

Secondary Glazing Systems Fact Sheet

For medium-to-large sized existing commercial buildings, secondary glazing systems can achieve about the same performance as replacing windows with new high-performance models, but for about half the cost. These products attach to the interior side of existing windows, improving occupant comfort, health and wellness, while significantly reducing energy costs. Secondary glazing systems are professionally installed and far less expensive and disruptive to occupants than undergoing a full window replacement.

View Fact Sheet

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