High-Performance Window Choices on the Upswing

December 29, 2013
January/February 2014
A version of this article appears in the January/February 2014 issue of Home Energy Magazine.
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Last July, two California companies made a splash in the residential window-manufacturing industry when they announced that their new energy-efficient windows had been certified by the Passivhaus Institut (PHI) in Germany. Casagrande Woodworks and Wooden Window were the first U.S. manufacturers to win this recognition, and it meant that their windows met the requirements for recognition as a Passive House (PH) advanced component. These certifications, however, are just highlights among the growing availability of very high-quality, energy-efficient windows in North America.


This NorthWin window is well suited for Canadian climates. (Guido Wimmers)

Table 1. PH Windows Available in North America

When the first PHs were being built in the United States less than ten years ago, builders had a small selection of imported window choices that allowed them to get the high R-values and solar heat gain coefficients (SHGCs) required for their buildings to meet the PH standard. Today, builders and designers can choose from a variety of very energy-efficient windows—with at least three now manufactured on this continent.

The PHI, which was founded in 1996 to conduct research and promote the design and construction of very energy-efficient buildings, instituted a certification program for PH components in 2000. Certification programs are well-recognized tools for stimulating the market to develop products that meet specified performance and quality standards. In Germany, and gradually in many other countries, manufacturers have risen to the challenge. By 2013, manufacturers in 22 countries in Europe, North America, and Asia were producing 232 PH-certified transparent components, of which 119 were PH-certified windows.

The First PH-Certified Windows Manufactured in the United States

At Casagrande Woodworks, President Jeff Casagrande started researching European window machinery in 2007 and started manufacturing windows in his facility in Paso Robles, California, in 2011. In 2012, when the idea of building a PH window was already taking shape for him, he attended a workshop for window manufacturers hosted by Passive House California, an educational organization. The intent of the workshop was to stimulate local window production. For Casagrande, it succeeded. He left the workshop thinking that this was a market with the potential to grow. In Europe, customers can choose from more than 100 high-quality PH windows, many made by small manufacturers. But that’s not the case here. In addition, many Americans prefer outswinging windows, which European manufacturers don’t make.

These ideas came together, and Casagrande, working with partners Soukup America, Zuani, and Rangate, created Synergist—a wooden, outswing casement window certified to meet the PHI’s advanced component criteria. Assuming a glass R-value of 6.3 and a window size of 4 feet x 4 feet 10 inches, Synergist as a whole has an impressive U-value of .79 watts per square meter per degree Kelvin (W/[m2K]), or an R-value of 7.1. As originally designed, the window is suitable for cold climates, but by swapping out the glass, Synergist can be adapted for most climate types. The window frames are made from western red cedar or reclaimed redwood, with a strip of cork insulation and Spaceloft, an insulative material with a very high R-value per inch. Aluminum-clad wood frames are also available. Automated, privacy roll-down shades and insect screens can be built into the window frame if desired. Turnaround time for orders generally ranges from 10 to 14 weeks, although it can be as little as 8 weeks, depending on the size of the job.

Larger window companies are noticing the increasing interest here in high-performance windows and expanding their product lines in response.

At Wooden Window in Oakland, California, President Bill Essert trod a similar path leading to the production of CaliPassiv, an outswinging wood-framed window also certified by the PHI last July as an advanced component. Wooden Window has been constructing and restoring custom windows and doors for more than 30 years. The company has all of the latest robotic fabrication technology, so it wasn’t that much of a leap from custom-manufacturing historic replacement windows to engineering and producing more forward-looking, high-performance windows. Essert also attended the 2012 workshop for window manufacturers hosted by Passive House California, which further inspired him to engineer a high-performance window that would be right for American customers.

The triple-pane, aluminum-clad, wood-framed CaliPassiv window uses compact foam for insulation and multipoint locking hardware made from stainless steel. According to the PHI’s certificate, assuming a glass R-value of 6.3 and a window size of 4 feet x 4 feet 10 inches, CaliPassiv achieves a U-value of .78 W/(m2K) (or an R-value of 7.2). This window is suitable for a wide range of U.S. climate types.

Wooden Window has also designed a window that is value engineered for California’s more moderate climate areas, the CaliComfort window. This is a double-pane window with a gap between the two panes—18 millimeters or 0.7 inches—that is wider than is commonly found in American double-pane windows, in order to improve the window’s thermal performance. The sash is insulated but the frame is not. Like the CaliPassiv, the CaliComfort is an outswinging model. The bulk of the materials used in both windows are sourced in California. Turnaround time for Wooden Window’s custom-made windows is six to eight weeks.

Essert has toured many window manufacturers in Germany over the last 15 years, studying their technologies and practices. Most were small, family-owned businesses that were similar to his own company—and he found them inspiring. Many German window manufacturers are thriving by filling a local market’s needs for high-performance, energy-efficient products in a country where a triple-pane window is rapidly becoming the standard. As the demand for net zero, PH, or generally high-performance residences grows in this country, so does the interest in high R-value windows, as both builders and homeowners appreciate how much windows affect the overall building envelope (see “Why Buy PH-Quality Windows?”).

PH-Certified Windows in Canada

While Casagrande Woodworks and Wooden Window may be the first manufacturers in the United States to gain PHI certification, they aren’t the first window company in North America to do so. That honor went to NorthWin, a window company based in Vancouver, Canada, which designed and sells the Vision window, which was certified in 2012. To date, the window is produced only in Lithuania, but the company hopes to bring production closer to home soon. Guido Wimmers, a partner in NorthWin, says that the company started importing windows in 2007 and then turned to designing its own, because there were no PH-quality windows available in Canada that were well suited for Canadian climates. Wimmers is also cofounder with Michael Isaacs of the Canadian Passive House Institute (CanPHI), an educational organization that hosted one of the larger PH conferences in North America last September.

NorthWin’s certified Vision window represents what Wimmers calls the third generation of PH windows. The first generation had bulky, thick frames. At that time, window manufacturers essentially used a traditional approach and simply added more insulation to make a window meet PH quality standards. Second-generation PH windows were more slim and elegant. The third-generation PH windows are much different, says Wimmers. To maximize the glazing area, manufacturers are making frames that are horizontally oriented, taking up less of the window area when looked at from the side and yet still delivering outstanding thermal performance.

Why Buy PH-Quality Windows?

Windows are the weakest link in just about any building façade in terms of heating and cooling energy losses. Indeed, as a rough average, 50% of a building’s heating or cooling energy exits out its windows. As Jeff Casagrande from Casagrande Woodworks says, “You hear about the amount of oil flowing down the Alaska pipeline that goes out our windows, and it could easily be one-third less, if we can just get people to pay attention.” While it is always great to have better-performing windows, when does it make sense to make the leap to PH-quality windows?

That depends on the climate in question, and the cost. In a cold climate, an optimally performing window is essential for a high-performance building envelope, reducing heat losses, drafts, and condensation problems. While a high-performance window is expensive, it can reduce other costs. Using a mediocre window would require building better-insulated, thicker walls and roofs in order to compensate for the windows’ losses. In Canada, for example, better windows could mean not having to build a 24-inch wall, and instead using an 18-inch wall—a significant cost reduction, says NorthWin’s Guido Wimmers.

In a relatively mild climate, such as Santa Barbara, California, the highest-quality window might not make sense from an economic point of view. Homeowners might just need a window that is good enough to minimize heat transmission and prevent air leakage. Windows with multipoint locking systems seal more effectively than windows that slide shut or have only one lock.

Then there are quality considerations and aesthetics. Is the frame and locking system durable enough to provide years of service? In heating-dominated climates, windows not only serve to provide ventilation and light, but also serve as passive-solar thermal collectors. Fewer, larger windows bring in more passive-solar heat than do many smaller windows, but very sturdy frames and durable hardware are required to handle the weight of large areas of triple-pane glass.

For all Canadian climates, outstanding thermal performance is critical. That’s why NorthWin designed the Vision window, which delivers an R-value of 8.7, while its frame takes up only 3.5 inches. According to the PHI’s certificate, assuming a glass R-value of 6.3 and a window size of 4 feet x 4 feet 10 inches, the U-value for the whole window is .75 W/(m2K) (an R-value of 7.6). As Wimmers says, windows are becoming more specifically designed for certain climate zones, and NorthWin intended its window to be suitable for the coldest. NorthWin also wanted to stake another superlative claim—using only the most environmentally friendly materials—so the frame is made from wood and insulated with cork.

Although NorthWin planned to manufacture its Canadian-suitable window in Canada, the production costs there were prohibitive. According to Wimmers, triple-pane glass cost 80% more in Canada than it does in Europe. Turnaround time to receive orders is typically 10 to 12 weeks. NorthWin also imports windows and doors manufactured by Internorm in Europe.

Reaching Mass Manufacturers

Larger window companies are noticing the increasing interest here in high-performance windows and expanding their product lines in response. “We’ve been looking at Passive and watching it closely for the past year or so,” says Brenda Brunk, product planner for Marvin Windows and Doors, which is based in Minnesota. “We saw an opportunity to enter that market, to provide a U.S.-made product that had a more traditional operation and aesthetics that customers are more familiar with.” In June 2013, Marvin unveiled its Passive product, which is a customized version of its Ultimate push-out casement window, with triple-pane glazing and low-e coatings selected to deliver SHGCs in the range of .34–.42. This product is intended for use in Southern climate zones and is certified as such by the Passive House Institute US. Marvin is currently seeking PHI certification. Its Passive window has an all-wood frame that is clad with extruded aluminum on the exterior. Turnaround time for delivery averages three weeks, unless a customer wants a custom color or wood species.

Another U.S. company, Alpen HPP, has had its high-performance fiberglass windows accredited by the Passive House Institute US. Based in Boulder, Colorado, Alpen HPP was founded in 2012 when Serious Energy, which had been selling its Serious fiberglass windows, sold its fiberglass window business.

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For questions on this article, contact the author at mary@lowcarbonproductions.com.

For more information on the Passive House Institute US, visit their web site at www.passivehouse.us.

In addition to these North American-based companies, there are many more European-based companies selling and distributing PH-certified window products on this continent (see Table 1). There are also windows manufactured by other companies that are suitable to be used in a PH project, depending on the climate, but that are not certified. With the choices of window products multiplying, the growth should benefit consumers in all sorts of ways.

Mary James is the publisher at Low Carbon Productions and former publisher of Home Energy. She is the author of several Passive House books, available for purchase at Home Energy's store.

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