Alternatives to Insulated Glass Units
After experiencing off-gassing, leaking, fogging and deflection (glass warping) problems with IGUs, the simplicity and reliability of single pane windows is looking extremely attractive. Recently replaced six 46″ x 40″ x 1/2″ IGUs. Within a few weeks 4 of 6 IGUs cloud after the heat of the afternoon sun. Windows are west facing in north Florida (St Johns county). Believe this fogging is from off-gassing. By dawn the next morning, windows are almost completely fog free. Previous IGUs were replaced due to deflection (warping) from persistent heating and cooling over the years. These windows bowed as much as 1/2″ which provided a space for water to penetrate. Have been told deflection is a safety glass characteristic. However, strong windows are desired due to the possibility of hurricanes. Need glass that is strong but stable when heated and cooled. This has led me to impact (SGP laminated) glass. However, the local glass provider has told me my current IGU frames will not support the weight of impact glass. All of the proposed solutions have a major short coming. Regarding energy efficiency, the main issue is solar heat gain. Window treatments that block the sun generate enough cooling to provide reasonable AC bills and a comfortable room. Suspect going from double to single glazing will not significantly change room comfortability or energy bills. Does anyone agree with me? Do any of my points have merit? If so, how can I replace IGUs with SGP impact glass? What about replacing IGUs with polycarbonate – might that be an option? Also, what are the building code issues. Looking forward to reading some great ideas!
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I think by "off gassing" you mean the IGU is loosing whatever inert gas it was filled with? This isn't normally what is meant by "off gassing" -- "off gassing" usually refers to something releasing a contaminant into the air in gaseous form, like the smell you get from adhesive until it's fully cured.
If your IGU had vented, the fog would NOT clear. Once water vapor finds it's way inside the IGU, you have persistant fogging under nearly all conditions. Since the fog you see clears, chances are the glass pane is dropping below the dew point at some time during the day, and once that happens, moisture in the air will condense out onto the windows. If you're running air conditioning during the day and have very high outdoor humidity levels, this will make fogging in the way I just described more common.
Single pane windows are drastically less energy efficient than double pane windows. I strongly recommend you stick with quality double pane (or better) windows. I suggest looking for an IGU that incorporates a pane of laminated glass (note that sometimes the "soundproof" windows are an option here). You should be able to find some products that will work since building codes in hurricane zones frequenty require impact rated window assemblies.
Polycarbonate is durable and insulates a little bit better than glass, but it's much more prone to cracking, and it does not hold up as well over time when subject to significant UV exposure (a fancy way to say it doesn't last as long in the sun as glass :-). Polycarbonate is also much less stiff than glass, and it's more likely to bow and flex, and that physical distorion is one of the things you said you wanted to avoid.
Hi Bill, Thanks very much for your helpful reply. Here's what I understand about "off-gassing". It's a physical state transition from solid to gas due to heat or pressure changes. The materials inside the IGU (e.g. spacers, seals, gaskets, desiccants) can give off a gas when subjected to temperature or pressure changes. When my IGUs are heated by the afternoon sun, materials inside the IGU emit gas. I can see the gas cloud form as the window heats. Around sunset as the window temperature begins to decrease the gas is most visible. Through the night, the gas returns to equilibrium so the IGU is mostly clear by the next morning. As the process repeats, some residue accumulates inside the IGU so they are not as clear as new. No liquid/condensation has ever been visible. Suspect the IGU seals are intact and secure. Please let me say I am no window expert, nor a chemist. I'm a house handy, software engineer that reads what I can find on the Internet. I know enough to be dangerous. That's why I'm on this website hoping to get good ideas from real experts with real world experience. I have learned how problematic windows can be. Anyone designing, building or renovating windows better keep it simple or get help from people much skill and experience. I read, according to a large survey, the majority of people who replace their windows are unhappy with the outcome. Now I can understand why. All the advise so far says to stay with IGUs. You pointed out many of the single glazing short comings. Thanks! Believe my IGU replacement failed because I didn't know enough to buy good IGUs. Did not realize the quality varied that much. I did ask my window supplier who the manufacture was. Should have moved on when I did not get an answer. Specifically asked about Cardinal. If the solution to my window problem is getting better IGUs, what do I need to know about IGUs? Maybe there is already a relevant thread on this site. I need to search. Akos says go with Cardinal and aluminum edge seals. This sounds like important info! To reduce deflection (bowing from suns heat) I've been told not to use safety glass. This however is a problem in a hurricane zone. Maybe a laminated outer lite is the way. Still have UV and solar heat gain issues to minimize. Window suppliers void the IGU warranty if tinting is applied. Hence SHGC coating. This however means new IGU color would not match other windows. Solutions to all requirements are conflicting. One solution fights the other. Need a many faceted expert to tie all the solutions together. How do I find such a person? I know I'm not the first person to deal with these window issues.
Off gassing usually means things coming out that shouldn't, which is usually solvents evaporating out over time as the material cures. What you're referring to, "solid to gas", is phase change -- not really the same thing, although somewhat similar in concept.
You cannot see a gas, at least not any gas you're likely to encounter here. If you see fog/haze, it's almost certainly water vapor -- and remember that water VAPOR can exist even when you don't see CONDENSATION on the glass. If you're seeing water vapor INSIDE the IGU, then you have experienced seal failure with the IGU. That's pretty rare to have happen with a quality IGU, so you might have an IGU made "in house" by a smaller vendor that doesn't have high quality seals.
I completely agree with Akos' recommendations about sticking with a quality IGU manufacturer. Another potential option is that I have heard that Andersen is again making their welded IGUs, which are made by melting the glass panes together at the sames (a glass "weld"), so there is no seal to fail -- you have an all-glass assembly. The tradeoff is the welded IGUs are expensive. My old house had 50+ year old welded IGUs that were in perfect condition though, so they do last.
I think you have purchased some some standard IGUs. I would pick up units made by a major glass supplier (ie Cardinal), they will last. If you have a lot of sun exposure, I would avoid some of the warm edge seals as not all hold up well in the sun. Older style aluminum edge seals also hold much more desiccant which means they last longer.
In your mild climate, there is no need for argon fill, you can use regular glass but select low SHGC coatings to limit solar gain.
I think the glass in 3 windows and in a 12 foot sliding door failed in my house in Florida within 10 years of construction. Speaking to my neighbors, it was/is very common. That house was built in 2004.
With my NY home, it took 40 years for one Andersen window to fail.
Go with as good a window as you can afford and hope for the best.
The IGUs fogging/clouding so quickly (just a few months) after installation was a surprise. Also 4 of 6 IGUs with fogging is pretty consistent. These IGUs are not gas (e.g. Argon) filled. There is air between the lites, right? Wondering about the atmospheric conditions inside the IGU, when IGUs were manufactured. What about pressure differences between manufacturing site and install site - is that a concern? What if IGUs were made in Denver and installed at sea level? What if the humidity was too high at the manufacturing site? Imagine that is well controlled in a clean-room. Could what I think is off-gassing be caused by moisture that was sealed between the lites when the IGUs were made? I suspect the seals are good since the clouding comes and goes. This may be a dumb question, but how do people obtain quality IGUs? Do people generally order IGUs directly from Cardinal or Anderson then find a local installer? My IGU provider would not discuss IGU manufacturers. Current defective IGUs with installation were about $700 a piece. Tinting voided warranty.
So much to address here, not sure where to start.
There are probably well over 50 different spacer options available just from IG manufacturing in North America, metallic, non-metallic, and a boatload of hybrid options.
You do not want an aluminum spacer, you want stainless steel. But many folks who aren't actively involved in the industry understandably aren't well versed on the differences and advantages of stainless over aluminum.
And since Cardinal was mentioned several times a bit of history on Cardinal IG system and spacers.
About 1/3 of all IG's manufactured in North America come from Cardinal using glass manufactured by Cardinal, LoE coatings, tempered glass, laminated glass, and straight up annealed glass in IG units all manufactured directly by Cardinal.
Cardinal introduced stainless steel XL for their IG units in 1993, replacing aluminum spacers that they had been using until then. When Cardinal introduced the XL they predicted seal failure rate of .25% at 20 years and .5% at 50 years. As of 2022 and almost 30 years of field data using the XL, seal failure rate is pretty steady at about .2% or a bit better than they had predicted for 20 years. In 2014 Cardinal introduced the Endur stainless steel spacer which is an upgrade on the original XL predicting a .2% or lower failure rate at 20 years.
The original welded glass IG units really are amazing. There were two manufactures of those units, PPG and LoF, however neither one of them even exist anymore, caveat that PPG glass assets were acquired by Vitro about 10 years ago and are still operating as part of that company.
In any case, not sure where the idea may have come from that Andersen was making their own, but they never made them in the first place, and they aren't making them, nor is there any indication that they are planning to do so now. Logistically it would be a near impossibility. Andersen is almost exclusively a Cardinal customer except for a few small niche products such as blinds or artglass between the glass panels inside the IG unit, things that Cardinal doesn't offer.
You mention in your earlier post about offgassing:
"The materials inside the IGU (e.g. spacers, seals, gaskets, desiccants) can give off a gas when subjected to temperature or pressure changes. When my IGUs are heated by the afternoon sun, materials inside the IGU emit gas. I can see the gas cloud form as the window heats. Around sunset as the window temperature begins to decrease the gas is most visible. Through the night, the gas returns to equilibrium so the IGU is mostly clear by the next morning. As the process repeats, some residue accumulates inside the IGU so they are not as clear as new. No liquid/condensation has ever been visible. Suspect the IGU seals are intact and secure."
What you are describing is called "chemical fogging" not to be confused with moisture fogging, something that not all IG manufacturers appear to completely understand.
Before any material is okay for use in an IGU system it should be tested for the potential for outgassing within the IGU airspace. There is a specific test procedure called the Fog Box Test, and rather than go into details, here is a better reference than I can explain it: https://www.cardinalcorp.com/source/pdf/tsb/ig/IG10_08-2020.pdf
"The IGUs fogging/clouding so quickly (just a few months) after installation was a surprise. Also 4 of 6 IGUs with fogging is pretty consistent."
Who is the window manufacturer? And we are talking fog between the lites and not not the glass surface, right?
"These IGUs are not gas (e.g. Argon) filled. There is air between the lites, right?"
Was this what you were told or otherwise know somehow? There has to be something between the lites, if not argon, etc. then it could be straight up air.
"Wondering about the atmospheric conditions inside the IGU, when IGUs were manufactured. What about pressure differences between manufacturing site and install site - is that a concern?"
For you, no. For someone in Denver or higher, could be but not for the reasons that concern you.
"What if IGUs were made in Denver and installed at sea level?"
That could be a concern, again for reasons other than you describe, but it is VERY unlikely to be the case. Again, who is the window manufacturer?
"What if the humidity was too high at the manufacturing site?"
Not a problem, IF....(see your next question), otherwise if the unit is closed and sealed in ambient then whatever is outside the IGU is now inside the IGU.
"Imagine that is well controlled in a clean-room."
Not precisely. Some manufacturers do close and seal IGU's in room air environment, but the better ones use automated equipment that finishes the unsealed IGU in an enclosed air chamber, evacuates ambient air, then fills the unit with argon (or whatever) and then seals the IGU. If the unit is going to have an air fill then (often depending on manufacture and equipment) the ambient air is evacuated and the unit will be filled with dry filtered air.
"Could what I think is off-gassing be caused by moisture that was sealed between the lites when the IGUs were made?"
Potentially yes but more probably no
"I suspect the seals are good since the clouding comes and goes."
Perhaps? Probably? Maybe? But no way to know for certain without testing, and ultimately it doesn't matter in any case if the IG is bad due to chemical (or some other cause) fogging.
"This may be a dumb question, but how do people obtain quality IGUs?"
Not dumb at all, but the easiest answer is simply to buy windows from a company that uses Cardinal or else manufactures or purchases a high quality IGU elsewhere. Acquiring an aftermarket IGU is a crap-shoot and the odds are far from in your favor. Cardinal only sells to window companies and not directly to regular consumers or to sources that supply ordinary consumers. With the caveat that nothing is 100% and sometimes there are loopholes.
"Do people generally order IGUs directly from Cardinal or Anderson then find a local installer?"
Many window companies, including Andersen (with an E), buy their IGU's directly from Cardinal or other IGU manufacturers and install it in their windows, while many other window companies manufacture their own IGU's. Cardinal supplies the complete system, basically plug-and-play to their customers, while other window companies source the components to build their own IG's. Any window company that sources a complete IGU from Cardinal is on equal footing with every other window company who buys from Cardinal. Big or small, quality or junk (window not IGU), they are all using the same IGU system in their window.
On the other hand for companies that build their own IGU's, often using Cardinal glass, while you should be able to expect a quality IGU from a high quality window company, I wouldn't anticipate a quality IGU from a low quality window company. That's simply reality.
I mentioned that Cardinal is about 1/3 of all residential IGU's in North America, the rest of the market is about the spacer they use, not the complete IGU. Meaning that about an additional 1/3 are made using Intercept spacer either plated steel or stainless steel (two versions) from Vitro (formerly PGT). The plated steel version isn't that good, the stainless steel version is much better. The remaining 1/3 are mostly aluminum or else either Superspacer or one of the "Dura" products, Duraseal, Duralite, or (shudders in horror) Swiggle, then everything else.
Disclaimer, I am retired and out of the loop so 1/3, 1/3, 1/3 is rather generalized, but should still be pretty close.
"My IGU provider would not discuss IGU manufacturers."
Maybe because he doesn't have a clue?
"Current defective IGUs with installation were about $700 a piece."
"Tinting voided warranty."
That doesn't instill confidence in any way.
Other much-more-knowledgeable commenters have preceded me, but if you want an insulated window with no inert gas, Pilkington Spacia windows eschew the gas in favor of a vacuum. They are thinner than standard two-pane windows, and are primarily marketed for use in historic buildings where thinner glass is more period-correct.
I'll try again to get the IGU manufacturer but I think your right about my window provider not having a clue. Fog is definitely between lites (inside IGU). As fog builds I can see the marks from the suction cups that held the lites. Before I purchased, provider confirmed IGUs would not be argon/gas filled. Good - I don't need to be concerned with IGU manufacturing location. Any chance the fogging/gassing could deplete itself and the IGU air establishes a new stable equilibrium without fog? Probably not. Does a list of professional IGU providers exist - like CPA and Engineering associations? I'd like to work with someone who has the proper training that I can trust. Believe my window provider knows they did me wrong. Even though I have not given them a hard time they are pretty much ignoring and stone walling. Definitely need to find another provider. Other IGUs on same wall have been tinted for 26 years without any problems. Believe the tinting clause is just an easy way to work with bad practices. Thank you very, very much for all the great information. Picture of the windows is attached. The bottom row in picture (top part of single hung windows along bottom) are the replaced IGUs with fogging issues. Original IGUs were replaced because they bowed around horizontal axis, causing leaks.
"Tinting voided warranty."
Which side is the tinting on? If the tinting is on the inside, it definitely can wreak havoc with the IGU especially one with a composite warm edge. Definitely something that would void warranty.
The inside tinting reflects a lot of the sun which can cause the temperature of the IGU to shoot up well above what they are designed for. This high heat can cause the plastic edge spacer and sealants to off gas and the IGU to swell. Asking for trouble.
The proper solution is to use low SHGC glass which puts the thermal coating on the inside of the outer pane which keeps the heat out of the house and out of the IGU. Even if you do get better IGUs, tinting them on the inside will most likely cause them to fail again.
Tinting is on the room side of the interior lite. There are conflicting views on the Internet regarding tinting of IGUs. Read one study that compared a control group with a tinted group of IGUs. Forget the time period (10 or 15 yrs?). The failure rate was about the same for both groups. Lots of variables involved. The old IGUs on this west facing wall have been tinted for 26 years without problems. The new IGUs were tinted and failed within a few months. Hoping new, good quality IGUs can last as long as the 26 year old IGUs. Didn't go with the SHGC treatment on new IGUs because we wanted all the windows to match in color. If I do-over, will not worry about matching color. Is SHGC coating the same as low-e? Does SHGC coating also block UV? Can that SHGC lite also be impact (laminated) glass? Would like the outer lite to block UV and solar heat gain while being laminated, annealed glass. Does that make sense? What should the inner lite be used for? Maybe block UV here? Sorry for all the questions. This gets complicated.
What is the best glass type to use in a hurricane zone? Annealed glass is too fragile. Safety glass warps (deflects) from the heat. Laminated-annealed glass looks to be the best option. Have seen how laminated safety glass crumbles. Not good in a storm. Looks like laminated-annealed glass hangs together better without being as dangerous as non-laminated-annealed glass. As mentioned, have had problems with safety glass warping from the heat. The non-warping IGUs in this wall are either smaller with same thickness (1/8") lites or larger with thicker lites. They have not warped. Only the uppers (47" x 40" x 1/2") in the single hung windows warped (all 6 of them). Can see the new IGUs pulling away from the frames already. Apologies for the rambling.
“Tinting is on the room side of the interior lite. There are conflicting views on the Internet regarding tinting of IGUs. “
There is some discussion as to whether it’s better to tint the exterior lite with Low-E on surface 3 or tint the inner lite with Low-E on surface 2, but most often it comes down to aesthetics, whatever the homeowner preference based on what it looks like.
From a technical point of view (and in my opinion) the coating should be on surface 2 keeping the heat out of the IGU, It can get HOT between the lites if the IGU is built with tint out and LowE in, but I suspect that I have probably seen more built this way than the other way around.
As Zephyr pointed out, non-metallic spacers are definitely more at risk of failure than metal, due to high temperatures, but Cardinal for an example has no concerns with their spacer failing due to high heat, but they strongly recommend using tempered glass in most cases when an IGU has both tinted glass and LoE coating to avoid glass breakage.
“The old IGUs on this west facing wall have been tinted for 26 years without problems.”
Are you certain that these IGU’s had LowE coating as well as tinted?
“The new IGUs were tinted and failed within a few months.”
“Didn't go with the SHGC treatment on new IGUs because we wanted all the windows to match in color.”
Not sure what you mean by “SHGC treatment”, do you mean the LowE coating?
“Is SHGC coating the same as low-e?”
Yes, the LowE coatings are designed for solar heat blocking depending on the number of layers of silver in the coating as well as level of tint in the coating when applicable.
“Does SHGC coating also block UV?”
Yes, the more layers of silver and darker the coating, the more UV blocking.
“Can that SHGC lite also be impact (laminated) glass?”
Yes, it’s very common.
“Would like the outer lite to block UV and solar heat gain while being laminated, annealed glass. Does that make sense?”
Yes, you can find that not uncommonly, but it might not be the best option, IMO. I strongly recommend the laminated interior, and annealed is fine for impact performance of the laminated glass. However, impact laminated glass is often manufactured using either heat strengthened or tempered for better structural performance during high wind events.
“What should the inner lite be used for? Maybe block UV here?”
IMO the inner lite should be the laminated, not the exterior. Laminated glass blocks better than 97% (depending on interlayer) upwards to nearly 100%.
“Sorry for all the questions. This gets complicated.”
No worries, it’s interesting and can be complicated.
“Laminated-annealed glass looks to be the best option.”
From an impact perspective, annealed laminated glass is a great option, and it’s very common, however for windload performance requirements, annealed laminated glass may not be strong enough.
“Have seen how laminated safety glass crumbles. Not good in a storm.”
All laminated glass is classified as safety glass, by definition, it doesn’t matter if it’s annealed, heat strengthened, or tempered. I suspect that you have seen the video or at least pictures and are describing tempered laminated glass that was broken while only supported on the bottom and it folded over.
In an actual impact rated window, the laminated glass is going to be held in place using extremely high strength silicone (or other) structural sealant. While tempered lami will break into cubes as you have seen, it will stay in place within the window frame, it isn’t going to collapse on the floor. It’s strong and safe no matter how breaks.
“Looks like laminated-annealed glass hangs together better without being as dangerous as non-laminated-annealed glass.”
Yep, that’s the idea of laminating glass whether in your home or the windshield of your car. First and foremost it’s a safety product.
“As mentioned, have had problems with safety glass warping from the heat.”
This one is a puzzler, and not to contradict, but what you are suggesting is physically impossible at even the highest temperatures than your windows could ever see short of a fire. Glass is tempered at about 700C and after tempering it would have to reach near 400F to affect it. Clearly you are seeing something, but it isn’t tempered glass warping because of heat exposure.
“The non-warping IGUs in this wall are either smaller with same thickness (1/8") lites or larger with thicker lites. They have not warped. Only the uppers (47" x 40" x 1/2") in the single hung windows warped (all 6 of them). Can see the new IGUs pulling away from the frames already.”
You have two ½” lites in the upper windows? At that size the IG’s using ½" glass would weigh in the neighborhood of 160lbs, or do you mean 1/8” lites in a ½" IGU?
Again not sure what you are seeing but something is clearly happening.
“Apologies for the rambling.”
Thanks again for all of the great information! This thread has been tremendously helpful. This time I'll try to stay focused on the warping of the tempered glass. There are 12 windows in this west facing wall. There is a horizontal row of 6 picture windows on top of a row of 6 single hung windows. The single hung windows, of course, have a fixed upper IGU and a moveable lower IGU. Of all these 18 IGUs, it is only the 6 fixed upper IGUs on the single hung windows that have warped. Question is why? My defective IGU supplier told me tempered glass is more in inclined to warp than annealed glass. Don't have 100% confidence in supplier but some of his comments have proven correct. Also read on Internet that safety glass can warp. I'll try to find that reference. My theory regarding why only the single hung uppers warped is because of their size to lite thickness ratio. Believe the uppers and lowers are made from the same thickness tempered glass (1/8"). Aside from being slightly smaller, the lower IGU is also framed differently. If memory serves, the IGUs warped around the horizontal axis. Have seen pictures of partially shaded IGUs shattering from temperature differentials. My IGUs pretty much get evenly distributed sun light. From earlier comments, glass strength to resist wind loads (hurricanes) is definitely a requirement. Also, having non-warping and non-leaking IGUs is a requirement. What are the most important IGU specs to meet these 2 requirements? Warped IGU dimensions are: 1/2" OA: 1/8" clear tempered / 1/8" clear tempered (with interior film tint), size 46-3/16" x 39-7/8". Thanks!
You are welcome, but before addressing IG units once again, I am going back to your original question....can you substitute an impact rated laminated glass lite using SGP for your current IGU's? What about energy performance/building code?
Your original question sort of fell off the road along the way.
The short answer is possibly yes because you live in a warm climate where your primary consideration is keeping cool and not staying warm.
And the longer answer...
When a LowE coating is encapsulated inside of a laminated package, coating against the interlayer, U-factor advantages of the coating are negated. Basically there is no U factor improvement over using clear glass, however the solar heat gain blocking properties of the coating are virtually unchanged. So laminated glass with embedded coating has been used for quite sometime in that application, but with U factor in the neighborhood of 1, it didn't do much to control ambient heat gain or loss.
Several companies came up with a way around this by laminating a softcoat SHG blocking coating such as 366 between the lites and a hardcoat such as Pilkington's Energy Advantage on surface 4 to improve U factor performance. Eventually coaters developed sputter surface 4 coatings such as I89 that improved U factor at least as much as the hard coat in that application but with better appearance, but the result was the same.
The combination of lami surface 2 for SHG and surface 4 for U factor was enough to meet code in many deep south locations, but not all, so I can't say for certain if you can use this option, but it is there.
Tinting can work two ways. One is to absorb the unwanted light and IR. The other is to reflect it. If it absorbs it rather than reflecting it, all of that energy goes into heating the glass. That's not good regardless of where it is positioned.
To me, that's a reason to get an IGU that comes with the tinting that you want, rather than getting it independently added. It will be designed to work well as a system and the warranty will cover that system.
Assuming monolithic (single glazed) laminated glass meets code, how do I go about getting frames made? Cardinal Sea-storm glass with SHGC (LoE3) appears to be what I am looking for. Would like to replace 6 single hung (~4' X 6') plus 6 angle top (~4' X 8') picture windows with Sea-storm glass. How do I get the frames that will hold this glass? What should these frames be made of? Currently, windows have aluminum frames attached to stucco walls. Could the current aluminum, picture window frames support Sea-storm glass? It sure would be nice to find a contractor that could order frames, glass and install. This project would be beyond the capacity of my local glass provider.
The easiest and most efficient way would be to buy new windows and have them installed in the current openings. Otherwise you could pull the old sash and replace the glass directly then reinstall the sash with the new glass.
Have you discussed this option with any local window replacement pros? I don't consider big box or companies like window world in that category.