On The Benefits—and Drawbacks—of VIG

Vacuum insulating glass (VIG) has been around for decades, yet it isn’t widely specified in the U.S. commercial market. While VIG has found a niche in historic retrofit applications as a result of its thin profile, light weight and energy efficiency, several factors are preventing architects from specifying the technology for other applications.

The Case for VIG

Russell Drewry, associate vice president for architecture firm HGA of Minneapolis, worked with VIG for the first time on the Milwaukee County War Memorial bird cage stair restoration project. Designed by FinnishAmerican architect Eero Saarinen in the 1950s, the original curtainwall included a single lite of ¼-inch wire glass.

“The owner was having a great deal of difficulty with condensation and frost in Wisconsin. They asked us to come up with a replacement enclosure for the steel curtainwall because the condensation caused a lot of rusting and paint degradation,” says Drewry, adding that while the framing and mullions appeared poor at a casual glance, the structure was actually in good shape.

The project team was looking for a replacement product that didn’t weigh more than ¼-inch glass because they weren’t sure if the structure could support additional weight. After considering several options, window restoration company Restoric LLC told Drewry about Pilkington Spacia VIG. It was chosen for the project because it allowed the project team to maintain the glazing channel size and reuse the existing glazing holes while providing improved energy performance. The VIG includes two 1/8-inch lites with a thin vacuum cavity and is only slightly thicker than the original ¼-inch glass.

“We eliminated condensation and, more importantly, we maintained the architectural integrity of the stair enclosure,” says Drewry.

Matthew Radune, project manager for Scott Henson Architect in New York, currently is working on his first VIG project, 111 4th Avenue in the East Village of Manhattan, a multifamily building. The project involves restoring all 685 of the building’s 100-year-old steel, double-hung windows. Radune found a VIG sample at his office while wondering how the windows could be restored rather than replaced.

He said the windows have a ¼-inch depth, so an insulating glass unit (IGU) wouldn’t fit. Without VIG, his team likely would have replaced the windows with aluminum frames and traditional IGUs, which would have a U-value of 0.30. VIG allows the steel windows to be restored, which is better in terms of sustainability. The steel windows combined with Pilkington Spacia Cool have a U-value of 0.18.

“Looking at carbon emissions related to the operational performance of the two window options, over a ten-year time period, the restoration option would have 57% less carbon emissions. On the level of the whole building, this would result in a savings of roughly 1,400 metric tons of carbon,” said Radune.

Architects’ Analysis

While VIG has thermal performance and energy saving benefits in addition to its ability to be used in thin, historical framing, Drewry says some architects may be apprehensive to specify VIG due to aesthetic considerations. He says VIG has tiny glass spacers which are especially visible when viewing samples.

“Once it’s installed you don’t see them. They are very important to maintain the vacuum but architects might be apprehensive about that,” he says. “… Another aesthetic concern is the little valve used to produce the vacuum. Each glass lite has a ½-inch button in the corner. That’s a visual obstruction that might cause objection but if the VIG loses its vacuum the button can recharge it.”

Drewry also pointed out that VIG lead times are long, so if a unit breaks, the project team would have to wait for a new one to be shipped. On the other hand, he sees an exciting opportunity for VIG to be used in hybrid insulating units.

“Hybrid units provide the performance of a triple-glazed unit without the weight, which is a huge disadvantage in triple-glazed units,” he says, adding that while the weight of VIG is an advantage, there are size limitations. Radune agrees that size limitations may be an issue for architects, especially those that prefer large expanses of glass.

Code Compliance

Kyle Sword, manager of business development for VIG manufacturer NSG/Pilkington, says the U.S. market tries to use the lowest cost solution to meet required specifications, and VIG is often higher performing than the target.

However, he sees this changing as voluntary codes such as Passive House become more popular in the U.S.

“To meet the energy goals in Canada for 2025 or 2030, we can’t get there with triple or quadruple silvers. On top of that there’s Architecture 2030 and OneNYC 2050,” says Sword. “… To hit these targets we’ll have to go beyond standard double glazing … We’ll have to go to triple glazing, VIG or a hybrid product to hit the performance levels people are looking to achieve.”

Local Law 97 in New York City could be the catalyst for further specification of VIG. It establishes protocols for assessing the annual energy use of existing buildings, new construction and major renovations and determines recommended penalties for buildings that are noncompliant with applicable emissions limits. Building owners can be fined beginning in 2024.

Radune says 111 4th Avenue is currently one of the worst performing building in the owner’s catalogue of buildings.

David Cooper, president of DJ Cooper Consulting in DeForest, Wis., says he’s spent the last 10-15 years trying to gain VIG acceptance from a codes perspective to get it ready for placement in the market.

“The product has been around for decades but its use is in the infancy phase,” he says.

There’s no ASTM standard for VIG, but Cooper says ISO currently is working on a second standard. ISO 19916-1:2018, Glass in building — Vacuum insulating glass — Part 1: Basic specification of products and evaluation methods for thermal and sound insulating performance, was published in October 2018.

Expert Insights

Aesthetics and lead times aren’t the only setbacks preventing widespread market acceptance for VIG. It’s also expensive to manufacture, which Peter Petit, CTO of V-Glass LLC, says is the number-one barrier.

“If the vacuum glass could be made less expensively I think it would have a very wide market. Basically it costs too much to manufacture for [it to achieve] broad market acceptance. It’s our belief that the cost of vacuum glass manufacturing is at least four times higher than conventional dual pane insulating glass,” says Petit, who has been doing research and development on VIG since the 1970s.

Cooper adds that once a higher-volume production line is available, the cost will drop. It could become cost-effective enough for VIG manufacturing to return to the U.S.

“VIG is a difficult product to make and requires precision in the manufacturing process … Making insulating glass units using an automated production line is getting to the point where companies only need two to three people and can crank out 1,000 units per hour.

VIG is nowhere near that,” he says. He attributes this to the high levels of quality control that are needed compared to the typical insulating glass line.

Petit started V-Glass in February 2008 in order to pursue an insulating technology for windows that could make a large impact. Currently, his company is developing a cheaper way to manufacture VIG using an oven-free method, as the oven is what raises manufacturing costs. The heart of the process is a rapid room, temperature-flexible metal foil seal with potential to lower manufacturing costs.

“Oven-based vacuum glass is very expensive inherently because of long cycle times to hold the glass at temperature, melt and solder it and then cool the assembly down from the high temperature,” he explains.

The method in development uses whisker spacerettes, rather than pillars, to keep the glass lites from touching. The spacerettes allow for relative pane movement which, according to Petit, prevents bowing.

Jordan Scott is the editor of Architects’ Guide to Glass & Metal. She can be reached at jscott@glass.com

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