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What is a VIG vs an IGU?

vig vs igu
Image Credit: 123rf.com

When it comes to windows everybody wants the most energy efficient glass. I read a recent study measuring the effectiveness of sextuple-pane glazing. That’s 6 panes of glass in one window! The numbers were not as impressive as I think a lot of people were looking for either because, in my mind, there is always the law of lessening returns.

With this insanity going on and people striving to reconcile living in a historic home with our desires to lessen our carbon footprint and achieve net zero in our homes what are the real solutions? We can’t seriously think that layering more and more glass is the solution, right?

Enter VIG otherwise knows as Vacuum Insulated Glazing which is a completely different idea than an IGU, Insulated Glass Unit. In this post, I’ll get into both and compare and contrast them so you can understand the differences and whether one or the other might be a good option for you.

What is an IGU?

An Insulated Glass Unit (IGU) also known as “double glazing” has been around for longer than you might think. The first patent for the design was filed October 12, 1934 by American refrigeration engineer Charles Haven. He dubbed the new invention a “Thermopane” which had two glass panels separated by an air gap and sealed around the edges with rubber strips.

In 1938 the Libbey-Owens-Ford (LOF) Glass Company partnered with Haven to begin manufacturing the first IGU’s in America, but they were pulled from distribution the following year due to frequent seal failure and fogging (a common problem with the technology still today).

Over the years, the basis of design has remained much the same for these windows, but the technology and materials have changed radically. Different spacers, sealants, desiccants, coatings, and gasses have been employed to make the window as energy efficient as possible with varying degrees of success.

Essentially, an IGU takes the age old idea of double glazing, traditionally done by adding a storm window, and combines it into the primary window. This essentially eliminates the need for a storm window, but it still struggles with performance issues unlike the traditional solution of a single glazed window with an exterior storm.

The main issues, for my taste, are about decreasing energy performance over time. Seals are never solid enough to last much longer than 10-15 years as the gas seeps out and moisture seeps in leaving a fogged and inefficient window that cannot be repaired or maintained. This leads to a regular cycle of replacing glass (or in many case full window units!) due to failed seals.

Condensation between the panes is a major problem with IGUs Image Credit: 123rf.com

This is extraordinarily inefficient and wasteful when you could have a single pane glass window with an infinite lifespan, or at the very least, the window can be repaired or maintained unlike IGUs. When you check the ROI on replacing single pane windows with IGUs it’s terrible, sometimes taking over 80 years to return the initial investment. It’s for these reasons I am not a fan of IGUs as a product in general.

What is a VIG?

A VIG or Vacuum Insulated Glazing, is a newer technology that I feel is perfectly situated to replace IGUs much the same way the MP3 replaced the CD. The CD was a necessary step in the development of efficient glazing, but I feel its time is limited.

VIGs combine two pieces of glass just like an IGU, but the difference is what’s between the glass. Micro spacers only 1 mm in size keep the glass panes apart and the edges of the glass are fused together with molten ceramic, providing a vastly improved seal with much longer lifespan than traditional IGUs. The air is then sucked out of the space creating a vacuum between the two panes of glass. The result is much higher performance in a much thinner design.

The performance is off the charts in both energy and sound blocking abilities.

  • Vacuum glass has a thermal insulation performance four times higher than an IGU and six times greater than that of a single pane glass. A normal VIG would provide thermal performance equivalent to a 14″ thick concrete wall!
  • Due to the existence of vacuum in VIG, sound transmission is blocked. Hence, its sound insulation performance is about 10 dB higher than that of a normal IGU.

The cost of VIGs is considerably higher than IGUs as there are fewer manufacturers making these products, but in time I feel that the price will come down as other players enter the market. One of the companies offering this technology is the Pilkington Spacia line of VIG glazing options.

The question comes down to you in terms of which direction you go. If we truly intend to build and renovate with the environment in mind we have to consider the big picture. Across 100 years what option uses the least energy and causes the least waste in the landfill? In my calculations, the options that meet these requirements most closely are either the traditional single pane window with exterior storm window or a VIG since both have extremely long lifespans and eliminate waste or decreasing efficiency over time.

What do you think? Tell me your thoughts in the comments below.

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7 thoughts on “What is a VIG vs an IGU?

  1. I have looked into purchasing these and have had zero success in finding a company willing to sell to an individual. Can someone direct me to a contact?

  2. On the item of sound insulation, does the vacuum create most of that benefit? It would seem like the thin profile would not be sufficient for a necessary air gap otherwise. What type of reduction in decibels are we talking about?

  3. A very interesting read, I haven’t heard of VIG before.

    I have a question though. The old houses in my home country in Eastern Europe have 2 sets of casement windows in each window opening, one set opens inside (pull it towards you), the other set opens to the outside (push it away from you). The distance between the sets is about 4 inches (100 mm). Each set consists of timber frames and is single glazed. Is it what you call secondary glazing?

  4. Wow. At 1/4″ thick, one could use these as replacement glass in vintage windows. Now, about that weatherstripping…

  5. VIG is being used in historic windows in the UK. The weight and sight lines are acceptable in historic buildings feasible to fit in their existing sashes.
    But it’s so expensive, even if you cheat with one panel in a sash and cosmetic muntins. Last year, typical 6 separate lites was around $1200.
    Scott- Perhaps you could use your influence through the Alliance to encourage Pilkington to offer a few standard sizes to suit the double hung sashes.
    Thank you.

  6. Great article Scott. You are one of the only intelligent voices I hear out there on windows and old houses. Nobody looks at the ROI and I’ve looked at peer reviewed studies, not funded by window manufacturers, showing the energy efficiency of single pane vs double and triple is only about 15%. It’ll take years to recoup that! Solar is the same. These technologies only make sense with new construction.

  7. This seems to me to perpetuate the scam that is the replacement window industry. It is well documented that much more energy is lost from around the windows and through the roof than through window panes. How do we know how long these windows will last if they are new? Will the frames degrade as current vinyl and wood ones do? If a pane gets broken, can I go down to Ace and get a replacement for $8 and replace it myself? I think there are very few applications that would truly benefit from this technology.

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