Secondary windows—also known as interior storm windows, insulating panels, or secondary glazing systems—are a cost-effective, high-performance alternative to full window replacement for commercial buildings with old, inefficient windows. Secondary windows reduce heating and cooling energy use by up to 20 percent and cost 30 to 50 percent less than window replacement (depending on the product and application).
How It Works
Secondary windows attach to the interior or exterior of an existing (i.e., primary) window, resulting in improved occupant comfort, health and wellness. They work by creating an insulating pocket of air between the existing window and new secondary window that significantly reduces air leakage, outdoor air infiltration and heat transfer. This results in fewer drafts, reduced outside noise, and significant energy savings. The addition of a low-e coating provides increased benefits by allowing daylight through, while reducing unwanted exterior heat gain and interior heat loss, which results in reduced glare and fabric deterioration from UV light.
30-50 percent less than the cost of full window replacement
Achieves the same performance as replacing windows with new high-performance models
Reduces a building’s peak demand, saving an average of 20% on combined heating and cooling energy use
Updates an older building to current code performance standard
Improves tenant comfort and wellness
Improves tenant comfort by reducing air leakage, heat transfer, and outside noise
Improves occupant health by decreasing outdoor-air infiltration
Improves tenant wellness by reducing glare and increasing access to natural daylighting
Note: Combining the installation of secondary windows with other upgrades can maximize energy savings and reduce project costs
Quick and easy installation
Little to no occupant disruption, secondary windows can be installed during or after normal operating hours
No demolition or abatement needed
Installs in as little as 20 minutes per window
Installs from the interior eliminating the need for intrusive scaffolding or large equipment
Creates a tight seal which eliminates the need for cleaning (for inoperable products); easy to open or remove for cleaning (for operable products)
Seamlessly matches existing window aesthetic
Matches the existing window aesthetic and retains the building’s current or desired look
There are several product options available with most being highly customizable, including for color, size and window type
They do not impact the building’s aesthetic—an important consideration for many historic buildings
Matches current window functionality with operable and fixed options
Secondary windows work best when paired with the following existing window conditions: clear, single- or double-paned windows; windows without low-e coating or tint; and existing frames in reasonable condition. They have proven especially effective for offices, hotels, schools and hospitals, for which occupant comfort and noise reduction are essential.
The Attachments Energy Rating Council (AERC) is an independent, non-profit organization whose mission is to test and certify the energy performance of secondary window products to help homeowners, architects, and builders make more informed decisions. This rigorous certification process includes product simulations, plant inspections, air leakage testing and individual product verification. SEARCH AERC CERTIFIED PRODUCTS >
A discussion with David Berg, Hurley Development’s former Property Management Vice President, on the transformative, year-round value of commercial secondary windows, their reliability during extreme weather events, and their surprisingly easy installation process.
Commercial secondary windows can solve a host of building energy and comfort issues, including thermal discomfort, exterior noise disruption, sun glare, draftiness, high utility bills, high peak load and HVAC system stress caused by extreme temperatures. However, studies show that secondary windows will provide the most benefit for existing buildings...
Secondary glazing systems (SGS) offer buildings owners the opportunity to improve existing window performance, increase tenant value and decrease operating expenses—all with virtually no disruption to ongoing building operations.
Secondary glazing systems (SGS), sometimes referred to as interior window retrofitting products, are a simple straightforward solution to improving the performance of existing buildings at a reasonable cost and without disrupting occupants. The vast majority of energy consumption in the commercial and residential building sector stems from buildings that are...
Secondary windows—also known as low-e storm windows, insulating panels, or secondary glazing systems—are a cost-effective, high-performance alternative to full window replacement for commercial buildings with old, inefficient windows. Secondary windows simply attach to the interior or exterior of an existing (i.e., primary) window for quick installation, resulting in improved occupant...
