Why Did this Window Break?

BusterlodeJune 3, 2014

Am I wrong?

This is a newly installed 2nd story Pella window that faces east in a newly constructed house situated at 8,300' in Colorado with a view that stretches far out over the plains (this is relevant.. I'm not just waxing poetic). We discovered this window had broken a few mornings ago, quite possibly the first morning that we'd had the blind--which is built into the window--closed against the morning sun. My theory is that the gas in the window was never equalized and the heat from the morning sun, that much greater because the blind was drawn behind it, increased the pressure between the panes such that the exterior pane broke.

In support of this theory:
1. An identical window of the same dimensions nearby exhibits a significantly bowed profile such that a straight edge rocks when placed against the window.
2. The glass has been pushed outward from the window, rather than being pushed inward by an external force. Zoom in close on this image and you'll see the edges protruding.
3. Without rock-throwing kids nearby, the only external factor that could have caused this break that I can think of is a bird flying into it. Sadly, this has happened on a handful of occasions in the distant past (this house replaces another that was burned in a forest fire), where the impacts have been startlingly loud, but they have never resulted in a broken window.

Does this sound plausible? Has anyone seen this happen before? Pella may argue that it was a bird or something, but I really don't think so. And if it was pressure, I need to have other windows equalized before they suffer the same fate.

Thanks for any ideas you may have.

This post was edited by Busterlode on Wed, Jun 11, 14 at 19:07

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PRO
Windows on Washington Ltd

It is plausible and without confirmation of any exterior damage (i.e. rock, foreign object, etc.) the pressure differential certainly can do that if it is extreme enough.

Should be a covered warranty item if it is not from an impact.

    Bookmark   June 3, 2014 at 9:03AM
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Busterlode

Thanks, Windowsonwashington. I appreciate your input. Nick

    Bookmark   June 3, 2014 at 5:51PM
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millworkman

Does a window with integral blinds even have gas infill?

    Bookmark   June 3, 2014 at 9:34PM
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Busterlode

Yes. It ends up being 3 layers of glass. One removable, the other two fixed.

    Bookmark   June 4, 2014 at 12:43AM
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PRO
Windows on Washington Ltd

+1

Sealed IGU with removable interior panel for the blinds.

    Bookmark   June 4, 2014 at 7:12AM
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oberon476

"My theory is that the gas in the window was never equalized and the heat from the morning sun, that much greater because the blind was drawn behind it, increased the pressure between the panes such that the exterior pane broke."

More like working hypothesis, but you hit that nail right on the head...that is exactly what happened.

At 8000ft installation, your IG units needed to to be either a) manufactured at a comparable altitude or, b) manufactured using either breather or capilary tubes to equalize pressure between the lites if they weren't produced at a comparable altitude.

In this case your IG units were put together in Iowa, which is a long way from 8300'.

Although up to this point the units were able to withstand the altitude change without failing, you are correct that closing the blinds helped to trap sufficient heat between the lites of the IGU resulting in gas expansion enough to break the glass.

The break pattern in your picture is an absolute text book example of a high internal pressure break.

You are absolutely correct that you need to equalize pressure in the other windows before you see more of this type of breakage.

You need to contact the window supplier or the Pella rep and find out if the IGU's are factory sealed, or if they have tubes that were somehow crimped or plugged. In either case someone needs to make arrangements to get those windows checked and if there is over pressure then get it fixed before you lose anymore of them.

If you do have factory sealed IGU's, then in my opinion it appears that someone, somewhere, may have made an error in sending them to your altitude...

    Bookmark   June 4, 2014 at 1:07PM
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Busterlode

Thank you for adding your detailed analysis, Oberon. I sincerely appreciate it. We obviously have quite a bit invested in these windows, and it sounds like we need to take a close look at what accommodations were made by the manufacturer for altitude.

    Bookmark   June 4, 2014 at 1:25PM
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PRO
Windows on Washington Ltd

Oberon is the man when it comes to glass.

    Bookmark   June 4, 2014 at 1:45PM
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Trapper1

Oberon is spot on. IGUs need capillary tubes at this altitude. No doubt the sales rep knew this. The tube may be plugged or the factory may have forgotten to install it. The bulging other IGU is a good indication that this is the issue.

On the other hand, glass plates have significant internal stresses built in and edge strength varies. It's a statistical thing, but a certain percentage of glass plates will break in the first year of service due to thermal stress (either from the sun or room-side infrared radiation). The unit could have failed for this reason even if it had a properly functioning cap tube.

    Bookmark   June 6, 2014 at 9:38AM
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Busterlode

Thanks, Trapper. I appreciate your added comments.

    Bookmark   June 6, 2014 at 10:49AM
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oberon476

Thanks Busterlode and thanks WoW.

Trapper,

Good comments on thermal breakage and edge flaws, but this one isnt a thermal break.

In this instance the glass failed because there was too much gas in it for the altitude. If it was thermal-induced the break pattern would be very different.

This is a very high stress break and in this case the IG popped like an overinflated balloon.

    Bookmark   June 6, 2014 at 11:52AM
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Trapper1

Oberon, yeah, looking at the break pattern again, I think you're right. It certainly doesn't look like any thermal stress crack I've seen.

Missing or plugged cap tube.

    Bookmark   June 6, 2014 at 3:58PM
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