Any chance you can get any pictures? If not, can you describe the cracks in a little more detail - where they are located in relation to the top/bottom/edges of the glass. When describing the cracks, please note if it is single crack or if it has multiple branches (suspect single), if the cracks go into the center of the glass or are parallel to the edge. When the craks come out from the sash what is the approximate angle of the crack to the edge of the sash?

How much glass is showing - measurements.

Also, please describe the spacer as bet you can.

And finally, how thick is the glass and is it LowE coated?

Is the glass that has cracked ever in sun and shade at the same time?

[quote]Is the glass that has cracked ever in sun and shade at the same time?[/quote]

How would this be possible?

That did sound odd, didn't it~

To clarify, were any of the windows partly in shade and partly in sun due to shading of direct sunlight on the window due to soffit or any other obstruction - where at least part of the window was was in full sunlight and part of the glass was in shade.

I've posted 7 (large) pictures at
http://webpages.charter.net/leeelson/pictures/windows

The cracks are hard to see on the full window shots but they generally start in an arc in each of 2 corners. The 2 arcs are joined by a long arc and where the arcs join, there is sometimes a small (2 mm) hole. The angle of the crack to the sash is generally 30-60 degrees. The glass is about 18" x 40". The glass is low-E and the spacer is "warm edge" and about 3/4" wide. The company invoice describes the glass as "3(7/8)3 CL LEA TES". They only say that the thickness is at least 3 mm. (More info at http://www.inlinefiberglass.com/product_windows_325ser_spec.htm). 3 of the 7 windows have part sun briefly, the others do not. Breakage occurred on different calm wind days.

One other observation: standing inside the house, I can see 2 reflections of inside lights at night. For some windows, one reflection (from the outside glass-the one that breaks) is distorted (magnified) more than the other. For the windows that have cracked, this distortion is reduced. This suggests to me that the outside glass is bowed out (due to over pressure?).

Thanks for your thoughts on this.

Here is a link that might be useful: cracked windows

leeelson,

Excellent pictures btw. Without trying to make light of your situation, I would find it very interesting to have those units in order to personally analyze the break patterns.

When analyzing glass fracture, the analyst has to consider several factors including fracture location in the glass - where it starts and how it runs; the angle of the fracture from both the face of the glass and the edge of the glass; the number of "branches" in the fracture pattern; and if it is an isolated incident or if it appears to be a pattern which also may include the location of the window(s) in the home along with any specific environmental conditions such as the glass being in partial sun and partial shade at the same time.

First, and as you already well know, you have a definite pattern multiple windows all with similar "unexplained" fractures. In addition, you have a number of lites breaking on different sides of the home with different exposure to sun and wind  the randomness of the locations also indicates a pattern - if that makes sense.

The glass fracture designs in your windows indicate low stress breakage. That implies that the amount of stress on the unit in order to break the glass was less than 1500psi. Typically, glass should not break at less than 1500psi unless there is a contributing factor such as a relatively significant edge flaw  usually a chip or a ding of some sort on the edge of the lite. You have several windows with at least some having multiple fractures radiating into the face of the glass from multiple locations.

If the cracks had run parallel to the edge of the sash I would have suspected that there was a possible issue with the sash being too tight on the glazing or else a problem with an insufficient glazing bead. While that doesnÂt appear to be the case with your units, multiple cracks radiating from several distinct locations on a number of different windows indicates to me that there may be a problem with how they were glazed into the sash  or (again) that there were several relatively significant flaws on the edge of several different lites. Unless this window company has no idea how to handle glass, then I would still opt for a glazing issue.

You mention that you are at 5100ft. I would be curious about the elevation of whoever sealed the IGUÂs; partly because you also mentioned that the window company stated that they did something "special" to the windows in order to help them acclimate to your higher elevation. Is there any chance that they told what they actually did?

Typically for higher elevations there are two primary options. First there are breather tubes and second there are capillary tubes.

Usually, breather tubes are aluminum, short in length, provide a relatively large opening for equalizing pressure, and they are sealed once the window has been installed. This is the type of venting unit that would be installed for a trip over the mountains because it allows the interior airspace of the IGU to breathe as pressure changes at different elevations.

Capillary tubes, on the other hand, are stainless steel, longer (~18"), have a very narrow opening, and are not closed at installation. They are left open to the air after the unit has been installed.

Although specific recommendations and usage are very much manufacturer dictated, as a general rule capillary tubes are used in dry, high altitude, environments to equalize pressure on windows actually installed in that environment. Again, they are not sealed when installed - they remain open to the air. At altitude the air is relatively dry and what moisture that does attempt to enter the IG airspace is limited by the design of the tube.

I suspect that your windows arrived on site sealed from the factory with neither breather tubes nor capillary tubes installed. My first question to the window company would be to ask if they used either breather tubes or capillary tubes. If they said breather tubes then I would ask when were they sealed and if they said capillary tubes then I would ask them to show them to me  they can be seen if you know where how and where to look. If they said neither I would then suggest that they made windows that were unsuitable for your environment.

I also suspect, if the IGÂs were sealed at a much lower altitude, that they have tended to bow outwards with the decrease in air pressure at the higher elevation. In addition, I suspect that you have had a good bit of wind where you live - the types of fractures that I see in the pictures appear to be "bending stress cracks" which indicates exactly what it sounds like  the glass was bent until it broke. Basically the crack acts as a stress reliever for the glass.

Bottom line, what I see from your description and pictures is several flaws in the glazing of these units. In their "normal" environment they might have been fine for a number of years but when subjected to the more severe environmental conditions that they are now in, the glass has cracked in an attempt to relieve stress induced by the severity of those conditions. The fact that there are numerous cracks  all low stress and all apparently independent of one another  indicates that there may be a significant edge issue as well as the bending stress issue.

Hope this helps  and I am more than a little curious to know the window company's response.

And what I failed to say in my previous post is that I am suggesting conclusions based on pictures and written descriptions and not on actual physical analysis of the windows.

While I am comfortable with my conculsions (within the limitations mentioned) ultimately I am guessing - educated guess - but still a guess.

You would need the units to be examined by a qualified glazing engineer to completely verify what I have suggested, but again I think that your picture and written descriptions are very compelling and I am comfortable with my limited analysis of your situation.

Thanks for your analysis. I will post the company's response when I get it.

One more observation. Placing a straight edge across a sampling of the windows, I find that the deflection (outward bowing) of the glass is 1/4" to nearly 1/2" across about 18" of glass. This seems like an over pressure indication to me. Is this normal?

Do all these windows face any particular direction? Like South and West? Any broken on the North side of the house?
Ron

Bowing such as you measured is another indication that the units were sealed at a lower altitude and that there is simply too much pressure between the lites causing stress on the glass.

Oberon, Toronto is about 275'. I'm sure their glass is made in house or at least locally. I can't believe they would send glass to 5100' with out some type of breather. This just boggles my mind. It's quite obvious they are exploding from gas expansion. Is Nevada in the same climate range for LOE application or is it in a heated climate? I would almost it's in the hotter climate with the LOE on the inside of the inside glass pushing the heat outward. By the looks of the pictures, the glass is blowing out along the pivot side of the window. I can understand the West window getting an uneven exposure to the sun. With the sun coming over the house I'm sure the eve is blocking the sun enough to cause the sun to hit the bottom of the window first, creating an uneven heating of the glass bottom first. The north side windows at this time of the year would more then likely never see the sun. So I'm assuming the barometric pressure change would have blown these windows out. My question to you is why didn't all the windows pop at the same time, considering the fill was even? Their website states their gas fill is only in the 60% range. Since the glass has cycled a year, it has seen the changes of the seasons. Why wouldn't all the glass have cracked. Is it do to glass size? I know smaller pieces of glass crack faster than the bigger pieces, but wouldn't they all have failed by now. Just curious on why this happens. Adding to the knowledge. Guy

The cracked glass has been on the north and west sides only. The south is entirely safety glass and probably much stronger. Don't know why the east side is unscathed. Also, windows seem to crack in neighboring pairs.

After several conversations with the manufacturer and the agent who sold us the windows, it is now clear that the windows should have had breather tubes installed and that there is considerable overpressure due to the altitude difference between sealing and installation locations. There has been some discussion of who should have specified high altitude windows, but to the company's credit, they say that this does not affect their resolve to make the problem right. (As an aside, Inline has gone to great lengths to fix other problems that have occurred). This issue did come up prior to the sale in my discussions with the selling agent and with the factory, but they assured me that 5000' required no special procedures. They now say that 4500' is the cutoff. What is amazing to me is that the agent sold similar windows to a job site near here (Tahoe) that is more than 2000' higher than we are (i.e. above 7000'). They've had no problems with breakage, which is hard to believe.

As to the fixes. They will, of course, replace the broken windows. They also plan to follow the recommendation of their glass supplier and retrofit the unbroken windows in the field by removing the windows and drilling a small diameter hole to the area behind the spacer. This will break the seal and allow pressure equalization. They will then seal the hole with a sealant recommended by the manufacturer. They claim that this brief exposure will not allow significant moisture inside due to a dessicant that was installed originally. This seems like a reasonable approach to me.

leeelson,

I think that their option is reasonable. By drilling the small hole they will be doing the same thing that a breather tube would have done and since you are at altitude moisture shouldn't be an issue.

Glad to hear that they are accepting the "blame" for this one. It really was fairly obvious what was happening. Again, your descriptions and pictures were excellent.

Guy! Good to see ya, Bud.
Good questions and I will offer a few words (well I rarely offer "a few" words...)

Glass has inherent strength - obvious.
Glass, by definition should be stronger than steel - obviously it is not.
Glass is filled with microfractures that is a characteristic of the material and these microfractures are the reason that glass isn't as strong as it should be.

Glass is a super-cooled liquid or an amorphous or non-crystaline solid - meaning that glass does not form a crystaline structure such as metals and other typical solids do. This non-crystaline structure is part of what makes glass transparent, but it is also part of what makes glass relatively brittle. Glass can be made to form a crystaline structure, but it changes the properties of the material significantly.

When I mentioned that the glass in leeelson's windows were likely to have significant edge flaws, I was not suggesting 2" breaks or anything gross, rather, and in the frame of glass manufacturing, I was thinking of chips and dings that could be 1/16" or even smaller...but, that had certain characteristics that would precipitate a crack in the right circumstances.

And I KNOW that you have seen your share of unexplained cracks over the years!

There are three main types or causes of glass fracture:

1. thermal stress
2. bending stress
3. impact

I won't go into number three since there is not likely to be anyone anywhere who hasn't experienced glass breaking from an impact!

There are also a few other types of stresses that can cause glass to fracture, but I also am not even mentioning them since they are relatively uncommon and this post is going to get detialed enough without going in the "trivia" route!

Thermal stress first. When glass is exposed to heat, it absorbs it. When glass absorbs heat, it expands. But, glass is not a good conductor of heat. In fact, glass doesn't like to share so that it is quite possible to have significantly varying temperatures within a single lite.

As long as the entire lite is exposed to high or low temperatures uniformly, no problems - but, if heat is not uniformly applied to the lite problems can develop.

It could be a window in partial sun and partial shade at the same time. It can be a window that is openly exposed to direct sunlight, but the edge areas of the lite are not exposed to the same temperatures because the edges are being covered by the sash itself.

It can be a tree or telephone pole casting a shadow across an otherwise solar-exposed window.

In any event, when exposed to heat, glass expands. When not exposed to heat, glass remains static. Now we have a problem. The difference in temperature between the heat-exposed portion of the lite and the unexposed portion of the lite can be significant and imagine what is happening to the stucture when one part of the lite is attempting to expand while the remainder is attempting to remain static! "Houston, we have a problem".

One characteristic of thermal breakage is that the intial crack will be 90 degrees or directly perpendicular with the edge of the glass - and 90 degrees or directly perpendicular with the face of the glass - until other stresses within the glass cause the crack to vary from that perpendicularness (I just coined a new word!).

Thermal stress in glass is calculated at 50psi for one degree of temperature difference. In other words, if the glass face, exposed to direct sunlight is at 100F and the edge, covered by the sash is 60F, then that particular lite has an induced thermal stress of 2000psi (40 degrees x 50 psi). A significant stress in the unit, obviously, but not usually enough to cause the glass to fracture unless there is a contributing flaw of some sort somewhere in the glass.

Okay, long enough for one post and I am being called to dinner, so I will continue later!

Very interesting Obi-One! I've dealt with the "Stress Fracture" for many years and never knew there were two methods in which they could occur. I always assumed they were caused by bending stress.

I understood the edge crack theory. I glazed more windows than I care to admit. I can remember a couple times when I saw a chip or tiny crack in the edge of a piece of glass. I never thought it would be an issue and glazed it in. The next morning I'd go into work and see my glass had cracked straight across. Never tried that after a couple times. I was only glazing double strength laminate glass at the time, I knew better with insulated units.

Thanks for the info, your the best! Baseball season is just around the corner. Twins should be starting their new stadium here quickly, can't wait to sit outdoors again like the good old days at the Met. Take Care my friend.

Hi again Guy!

Sorry my long explanation got cut off. I went on an extended road trip and didn't have a chance to get back to it.

If you (or anyone is curious) I can continue it - but not for a few days...

Really looking forward to the season starting up! I caught the Gopher / NoDak game yesterday - wish I hadn't since last week's Final Five against NoDak was a MUCH better game(in my not so humble opinion)

Take care Bud and see you later.

Interesting reading. I too have had a recent string of cracking, double-pane, double-hung windows (Eagle). They are at least 20 years old, one on each of the four sides of our house, and all cracked within a 4-week period. It's been cold here in Pittsburgh (below zero when the first one cracked), but it has also been much colder. I've contacted the manufacturer to find a local rep, but haven't gone beyond that. Any suggestions?

Is the glass in your windows bowing in? In other words does the glass appear to be concave?

Have you seen any moisture or frost in the center of the glass in any of your windows that cracked?

Do you know if they cracked at night or during the day?

If during the day were they in direct sunlight?

Does the crack come from the edge of the glass and does it appear to start out at 90 degrees from the edge?

Lots of questions...

Thanks for the quick response. I don't think I can answer all your questions, but here is what I know now after reading your post:

All the remaining, unbroken windows of the same type bow inward, suggesting a slight vacuum. The greatest deviation from flat was about 1/4 inch for a pane about 1ft x 2 ft in size.

For all the windows that broke, it was the outer pane, and pieces ended up between the inside pane and what was left of the outside pane.

We have never seen any condensation between the panes ever. Except for these latest events, they have functioned quite well.

For three of the broken panes, it appears that there is a point of crack initiation more or less in the middle; for the fourth, it is just a single, arc-shaped crack that starts and ends on the same edge of the pane (not 90 degrees - closer to 45.)

I guess my greatest points of confusion are 1) why now after 20+ years, and 2) why four events in just a very short time. These windows have experienced winters like this every year since they were installed. Can glass experience fatigue?

It is very odd that you have one on each side of your home. I am also a bit curious that it is the outer pane that broke in each window.

I suppose that there is no chance that someone might have broken them on purpose?

I would suggest that you call Eagle and tell them about the bow and the breakage. Currently Eagle has a 20 year glass / IG warranty, but I am not sure if your units have a 20 year warranty on them.

Some other companies that have had the collapsed glass issue have extended their warranties to cover that problem, I don't know Eagle's policy in that case.

Glass can fatigue, and being forced to remain under stress in an "abnormal" shape can certainly result in breakage in the right circumstances.

Again, I would suggest first thing is to contact Eagle and see what they propose.

Without getting too complex, it sounds to me, from my experience as a glazier of 33 years. That the windows were initially glazed or bedded with "silicone" which DOES NOT allow for any expanding or movement in the mainframe. When the frame moves the glass should NOT, it should set on rubber setting blocks (below both lites of glass at once) and be able to slide in the glazing channel while still maintaining a weather tight seal ie. (butyl sealant, is the best), and silicone does not allow this. And they just cracked from the undo "stress". Also, there may not have been enough clearance between the edge of the insulated unit and the sides of the glazing channel to accomidate the amount of movement. I see this in fixed panel PW's (sash set or direct set) and the tops of single hung windows all the time. Lower grades of glass (thank you NAFTA) are also being used causing more and more windows to crack. Good luck.....BG