By Gannon Sloves, Marketing & Administrative Assistant, Woodland Building Supply

Window design is absolutely one of the most critical components for achieving energy efficiency in homes. No matter how efficient your HVAC unit and insulation are, if warm air is pouring in or out around your windows, or radiating through, you’re going to feel it… right in the utility bill. Several factors influence the efficiency of windows: size, solar orientation, framing, glazing, coating, and more. Energy efficient windows can save a substantial amount of energy, as about 30% of a home’s heating energy is lost through windows and, in cooling seasons, about 76% of sunlight that falls on standard double-pane windows enters to become heat. Are you on the path to net zero? Sustainable window design also means optimizing heating, cooling, and lighting to save money and reduce your carbon footprint.

Types of Framing

Framing is key to window performance. The frame provides the seal that prevents energy from leaking into or out of the building. Wood frames continue to be the most popular option for insulating windows in homes. Wood framing is energy efficient, and the wood can be sourced from sustainable suppliers. Wood that is FSC-certified by the Forest Stewardship Council ensures that “wood is harvested from forests that are responsibly managed, socially beneficial, environmentally conscious, and economically viable.”

The downsides to wood framing include a higher price point and higher maintenance costs due to the re-painting that is routinely required to protect against water damage.

Aluminum is another popular option that is lightweight and relatively inexpensive. The downside of aluminum framing is that the metal conducts heat, which defeats the purpose of an otherwise energy efficient window installation.

You’ll find fiberglass a bit pricey yet very energy efficient, with little maintenance required. Fiberglass frames are airtight and prevent expanding and contracting, extending the life of your window.

Vinyl windows are made from PVC. They’re also high performing, with a lower price point, little required maintenance, and high energy efficiency, but…. The shortcomings of vinyl windows are their high carbon footprint and toxic pollution during production. And then disposal is harmful to the environment too. Vinyl windows expand twice as much as wood windows, meaning that they will have to be replaced in a shorter time period, because PVC cannot be repaired.

Fitting and insulation

Window seal failure is a common problem as windows age. Quality windows will open and close easily and retain their tight seal for at least a decade. Any air leakage can ruin the insulating attributes of your windows. Energy efficient windows must be designed and manufactured to tight tolerances, particularly around locking and sealing mechanisms. You should be able to feel that vault-like seal and latch as you close the window.

Proper installation is equally important to fighting air leakage. If your energy efficient window is fitted and installed properly—with no gaps, no rattling, and good weatherstripping—environmentally friendly wood windows are every bit as efficient as vinyl.

Pros and Cons of Different Frame Materials

(From Rajedran and Charde 2018)

Aluminum Frames

PROS: Light, strong, non-corrosive, easy maintenance
CONS: Rapid heat conduction, poor insulation
ALT: To reduce heat flow and U-factor insert a thermal break

Wooden Frames

PROS: High stability in structural and thermal properties; better moisture and decay resistance
CONS: High maintenance, attracts termites, expands and contracts in response to weather
ALT: Choose composite frames to meet difficult environmental conditions

Fiberglass Frames

PROS: Dimensionally stable; air cavities with insulation provides good thermal performance
CONS: High cost; labor intensive; color fading
ALT: Choose wood frames for lower cost

Considering all these options, the wood frame is the most sustainable and environmentally friendly option, and can be just as efficient as vinyl windows if installed properly.

Glass vs Glazing?

Glazing refers to the glass component of an energy efficient window. Double-paned windows with two panes of glass are referred to as double-glazed. Triple-paned windows, three panes of glass, triple-glazed.

Double- and triple-glazed windows are sealed with inert gases, such as argon or krypton, filling the spaces between the panes. These inert gases provide better insulation than just air and lower the U-value, or thermal transmittance of the glazing. A low U-value is critical for preventing heat loss or gain when the temperature outside is much colder or warmer than indoors. Argon and krypton are non-toxic gases that are denser than air, which is great for preventing heat transfer.

Single-glazed windows exist as a low-cost option. However, the glazing lacks insulation, making them far more transmissive of outside noises and temperatures.

Low-E coatings

To further ensure energy efficiency, a low-emittance coating, known as low-e, is applied to the glass. Low-e is a thin layer of metal or metallic oxide applied to the glazing of the window. Its purpose is to reflect heat either into the building or back outside depending on the type of coating.

In modern windows, spacers known as warm edge spacers, separate the layers of glass from each other so they remain in place. Spacers should ncorporate a thermal break into their design to reduce heat conduction. Warm edge spacers can be made from a variety of low-conductivity materials, including thermoplastics. These materials give the benefits of low thermal conductivity and high thermal efficiency, which help prevent condensation at the window edges.

Your best option is a well-installed, energy efficient window that is double- or triple-glazed, separated by an air gap, with a low-E coating on the glazing, and nonmetal spacers to extend the life and quality of the window.

infographic from Energy Star showing attributes of energy efficient windows

Energy Efficient Window Styles

You can certainly find an energy efficient window in the style you’re looking for. Contemporary windows work with various home styles. They come in casement and picture windows with all-white and all-black framing, interior and exterior. This black window style typically fits more modern homes capturing lots of natural light, with an elegant yet simple look.

Traditional windows include styles such as single- and double-hung windows with a traditional white or wooden finish, some featuring different grid patterns. This window style fits more classical style homes, offering a cheaper alternative to contemporary windows, while also being able to let air inside.

Contemporary window styles are usually larger, with higher initial cost plus additional maintenance costs. Traditional window styles are customizable, however, the look doesn’t quite compare to contemporary styles and may need to be replaced sooner. Both styles typically incorporate a mix of windows with the added benefit of reducing the solar heat gain coefficient, or G-value, which determines how much heat each window will introduce from sunlight.

Thank you to Quaker Windows and Doors for sharing beautiful images of homes with sustainable, energy efficient windows.

Efficiency Equals Savings

Window technology has been revolutionized in the past decade. Proper framing, installation, glazing, window styles, and a variety of external factors, such as solar orientation, all aim to extend the lifetime of your windows while saving energy and money for the consumer. With the right combination of window technology, it is possible to adjust solar gain, eliminate air leakage, reduce water damage, diminish noise intrusion, and eliminate excess heat transfer.

The environmental impact of choosing the correct windows is paramount. Beyond energy efficiency, reducing the lifecycle carbon footprint behind the production of the windows, as well as when the window is eventually discarded, helps to address the existential issue of climate change. Together with other green building products and strategies, sustainable, energy efficient windows can continue to evolve the construction industry towards a more eco-friendly future.

Home Depot stocks a wide variety of Energy Star windows for replacement and new construction. Check them out!

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