Photo by Lawrence Berkeley National Laboratory

A new breed of highly efficient triple-pane windows is drawing the attention of residential builders, who are interested in installing the products in the homes they construct as they pursue means for reducing energy consumption. According to industry representatives who attended a California Energy Commission (CEC) meeting this month, that was just one of the takeaways pertaining to how builders can comply with the state’s energy code. But demand from builders for so-called “skinny” triple-pane insulating glass (also referred to as “thin triple”) is slow owing to their cost, officials said.

Skinny triple-pane insulating glass (IG) is attractive to builders, because it’s essentially the same thickness and weight as double-pane glass, yet reduces the amount of energy it takes to keep a home’s indoor air temperature at comfortable levels. Windows equipped with the product also offer a key advantage over those with standard, triple-pane IG, because they can be installed into the same openings as double-pane windows, which means they don’t require additional labor to install, said Mazi Shirakh, decarbonization lead for the CEC. Windows with skinny triple-pane glass are suitable for single- and multi-family buildings, he added.

Windows that are better at insulating buildings are one of many tools builders can use to lower the Energy Design Rating of homes they build, which can help them to keep pace with California’s evolving building code and qualify for incentives from the state. Though other high-performance materials that help reduce heat loss can also enable builders to achieve these goals, windows are of particular interest, because they play an outsized role in determining how well a building keeps heat from escaping, officials suggested.

Although windows represent around 7% of a typical building envelope, they’re responsible for about half of the total amount of heat loss, according to Robert Hart, of the Windows and Envelope Group at Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif. While skinny triple-pane windows can help homes use less energy without the requirement for redesigning, they currently account for just a tiny fraction of the residential window market, said Hart.

“Window manufacturers have been able to build these products for quite a while, but they aren’t selling them,” he said, noting that skinny triple-pane windows accounted for less than 3% of the market in 2018, compared with the 90% share held by standard, double-pane windows. “LBNL is hearing that there is no demand because they are just too expensive.”

Another key factor affecting demand includes a lag between when California steps up energy efficiency requirements in its building code and when builders begin having to comply with the upgraded regulations, said Mike Hodgson, president of Consol, a Sacramento-based company that helps builders, utilities and government agencies develop energy-efficient buildings. For example, while the state’s building code will change again on January 1, 2020, permits for new homes submitted by December 30, 2019, will fall under the 2016 code, he said.

This means that rather than opt for higher-efficiency windows, builders can be expected to use less costly double-pane windows even after the new code goes into effect, said Hart. “Builders said they’re not required [to use triple-pane windows], so why bother if it costs more money.”

Sam Silverstein is a contributing writer for USGNN™.

1 Comment

  1. Thanks for reporting on this recent meeting that was introducing California home builders, the largest new construction home market in the U.S., to a new opportunity for using better windows. We think the article omits the key change in that market that provides a huge new business and sales opportunity for forward-looking window companies, beginning in 2020.

    The new T24 building code, effective for any new housing permit after 1/1/2020, makes only a small change on the maximum window U, reducing it from 0.32 to 0.30 – values that can be met by virtually all window companies with double glazing. But it also mandates a new high performance wall package that will require builders to fundamentally change the way they design walls, e.g. switch from 2×4 to 2×6 or add exterior rigid insulation. Hodgson reported at the meeting that this new wall requirement would add $2300-3500 per home. But 95% of builders meet the code using a “performance approach” and that tradeoff approach allows builders to replace the “wall package” with an “equivalent EDR window package” using a 0.20 U window, which requires a change to triple glazing. As long as the “0.20 window package” can be delivered to the builder at an incremental cost lower than the wall cost, ~$3000, it becomes a cheaper first cost alternative for the builder and they will shift to that option. For a typical home, that first cost translates into an added cost of ~$5.50- $7.50 per sq ft of window to convert the double to a triple.

    Some window companies offer triples now so have an immediate opportunity if they can meet or beat those target prices but some builders also complain that the added weight of these triples makes installation more difficult. Other companies who mainly offer doubles today could redesign their units to accommodate the wider, heavier triple IGU — that takes time and money. As a new option they could explore the “thin triple” IGU outlined in your article. This is a 3/4″ IGU, virtually the same weight as the double, that can be dropped into any existing window package. With a U~0.14 COG this IGU will result in window U values ~0.20.

    A few prototypes were installed in a builder’s model home in Fresno last winter without any problems. While there are some remaining practical challenges to be solved, we think this is a tremendous opportunity for window companies to compete effectively for a larger share of the builders’ $$ going into new homes in California. Beyond the immediate opportunity in California, these windows will have good energy savings paybacks in new and retrofit windows across the northern U.S.

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