Closer look: More construction to incorporate triple glazing

Change in codes and standards to spur increased specification
Sahely Mukerji
December 17, 2010
FABRICATION : CLOSER LOOK

Experts say more triple glazing will be used in construction, given the recent code changes in the national, state and local levels, and the Department of Energy’s continued push toward R-5 windows. DOE launched its Highly-Insulating R-5 Windows and Low-e Storm Windows Volume Purchase Program in May 2010, as part of a multi-year integrated strategy to transform the market for high efficiency windows, to facilitate the broader deployment of these windows.

Triple glazing penetration is approximately 3 percent in the residential market and less than 1 percent in the nonresidential market, according to the May 2010 “Study of the U.S. Market for Windows, Doors and Skylights” study from Ducker Worldwide, Troy, Mich. Those numbers will go up to 50 percent to 60 percent in the Northern Energy Star climate zones for residential applications, and less than 20 percent in the nonresidential market in the next 5-10 years, speculates Tracy Rogers, technical director, Edgetech IG Inc., Cambridge, Ohio.

Thomas D. Culp, president, Birch Point Consulting LLC, La Crosse, Wis., agrees. Triple glazing penetration will go up significantly due to code changes, he says. There are a number of drivers:  “First, green programs like LEED [Leadership in Energy and Environmental Design] and the new ASHRAE 189.1 and IgCC [International Green Construction Code] will drive triple glazing in northern areas, since they all require or reward increasing the energy efficiency beyond the primary energy codes: ASHRAE 90.1 and IECC [International Energy Conservation Code]. Builders usually go first to higher efficiency HVAC equipment to go beyond code, as it is often the easiest and cheapest.  But with the codes tightening up, they will be looking more and more to high performance envelope measures, including triple glazing.”

The above code programs are not just for a small subset of proactive building owners, Culp says. Now, they will be widely used for government and military buildings.  “Even the primary energy codes will be pushing triple glazing,” he says. “Once the 2012 IECC starts to be adopted and used, it will practically require triple glazing in zones 7-8, as well as further south for heavier products.” 

For the near term, the 2013 Energy Star/’Super Star’ revisions will be the primary catalyst behind the increased use of triple glazing in the residential market, Rogers says. “Additionally, there may be incentives/stimulus from the DOE to attempt to move the market in this direction, but this, of course, is budget dependent.”

Margaret Webb, executive director, Insulating Glass Manufacturers Alliance, Ottawa, Ontario, concurs. “We anticipate an increase in triple glazed units in order to meet the new requirements,” she says. “Thermal performance is based on window frame and IG. For existing frames, the only way to meet the new energy codes quickly will be to use triple glazed units.”

“Typically, triple glazed units are used in the northern climates, which is why they are more prevalent in Canada,” Webb says. “At the present time, triple glazing has a very low percentage in the U.S. market, but this will change as the energy codes become more and more stringent. Penetration in the Canadian market is greater than in the U.S., but to date, we haven't tracked statistics. I am seeing an increase in the number of triple glazed unit prototypes submitted to the certification program.”

IGMA is responding to the increase in manufacturer inquiries regarding fabrication of triple glazed units and developing new guidelines in response, Webb says.

Triples in the commercial sector

The first step for major energy performance improvement in the commercial sector is simply to mandate dual glazed, low-E, warm-edge in all commercial buildings, Rogers says. "Long term, the IECC and IgCC codes will mandate this level of performance [triple glazed] as energy codes continue to focus on overall energy reduction toward the 2050 net zero energy building goal.”

However, the commercial market likely will take twice as long as the residential market to see any significant triple-glazing impact, Rogers speculates. “The predominant limitation in this market is the size and weight of the units in a triple configuration. The significantly larger size of IGUs in this segment currently leads to fabrication and weight issues for triple-glazed units."

Robert Holcombe, director, Product Development, Kawneer North America, Norcross, Ga., agrees. "Triple glazing can weigh up to one-third more than a typical 1-inch insulating unit made up of ¼-inch glass," he says. "Heavier glass creates challenges for installers during installation of pre-glazed products, field glazing and/or re-glazing. The additional weight of triple glazing can also make balancing single and double hung windows difficult or cause wear and tear on projecting window hinging hardware. In addition, the costs for triple glazing are often higher than those of typical 1-inch insulating glass."

While some systems can be made to accommodate triple glazing with the introduction of a custom glass stop, many systems do not have the overall depth dimension to accommodate triple glazing with the additional thickness, Holcombe says. "Existing installations with standard 1-inch glass can also be difficult to retrofit for triple glazing."

Kawneer has been producing systems for triple glazing since the mid 90s, Holcombe says. These systems include the 7500 Wall with IsoWeb thermal break. Additionally, Kawneer’s 5500/5525 IsoWeb Fixed Windows and Vents have a triple glazed option. "During the first half of 2011, we will be launching a new curtain wall system with a triple glazed option," he says. "Kawneer has also designed job-specific custom 1600 Wall System1 applications that have used triple glazing."

Types

There are three kinds of triple-glazed configurations available today, Rogers says:

  1. Triple glazing with glass as the center lite, using traditional, individual spacer components in each glazing space. This configuration requires spacers to be independently positioned on the center lite of glass in such a way that the sightline of each matches and a ‘step’ is not created from one glazing space to the other.
  2. Triple glazing with glass as the center lite, using a single, U-channel profile spacer that captures the center lite, and seals between the inboard and outboard lites. Typically, such spacer components are flexible in nature and wrap around the perimeter of the center lite. The inboard and outboard lites are adhesively attached to the spacer sides to encapsulate the center lite.
  3. Triple glazing with a suspended film product such as Heat Mirror. The film is adhesively attached to a metal or metal/foam spacer. The film/spacer assembly is then attached to inboard and outboard lites. Once assembled with a structural secondary sealant, the unit is placed in a heated oven to allow the film to shrink and tighten to visible clarity.

“The ‘glazing gap’ or ‘glazing space’ is functionally the same as airspace, but these cavities typically have argon or krypton versus air,” Rogers says.

Triple glazing, at present, is still a specialty market, Webb says. In the nonresidential arena, Cardinal IG, Eden Prairie, Minn., AGC Flat Glass, Alpharetta, Ga., and Viracon, Owatonna, Minn., are a few of the big players, says Bob Spindler, vice  president, Technical Services, Cardinal IG, St. Louis Park, Minn. “For the residential market, the manufacturers are Cardinal and window manufacturers that make their own IG units.”

For traditional systems utilizing a glass center lite, there aren’t any “main” manufacturers of triple-glazed IGU, Rogers says. “Many IG and window manufacturers in Canada and the northern U.S. have triple glazed options available, but only provide them on demand. Most still have double glazed as standard. The suspended film alternative is primarily Heat Mirror at this time, so their fabricator list is the best source for this.”

An alternative to triples

Several IG fabricators are beginning to market IGU configurations that are double glazed with a sputter coat low-E on the No. 2 surface and a pyrolytic low-E on the No. 4 surface, Rogers says. “While this does provide for improved U-factor performance of the IGU, the rejection of heat by the No. 4 low-E coating also lowers the interior glass surface temperature by more than 10 degrees Fahrenheit. This has the potential to create problems with reduced condensation resistance of these systems and the formation of moisture on interior glass surfaces.”

Mark Hutchinson, manager - technical & sales support, Intigral, Walton Hills, Ohio, agrees. “There has been a great deal of interest in the use of surface 4 hard coat low-E along with a surface 2 soft coat low-E to generate lower U-factor performance for double glazing in the residential market,” he says. “The unofficial simulations we have performed for our customers using this configuration would generally agree with Tracey's assertion concerning condensation resistance.”

“We have done this make-up very successfully, says Don McCann, architectural design manager, Viracon. “However we do have to be cautious where we use this make-up, because you can have issues with CRF. This is dependent on the climate zone as well as the type of project you are working on.”

“While this practice is still relatively new and still under exploration, it may offer a potential avenue to get lower U-factors perhaps without having to jump to triple glazing and changing the framing to meet the specific project requirements,” Culp says. 

E-mail Sahely Mukerji, senior editor, at smukerji@glass.org.