Broken Window Pane-Any Ideas on Repairs(and how it might have happened)

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We noticed this one yesterday on the window above our bed in the bedroom. To be honest, we're stumped on it. It's the inside pane of a double pane window, and as can be seen it has spidered and broken out pretty well. The crack has grown since I took the photo(I have since shrink wrapped it to hopefully at least contain any glass shards should it fail completely).

We're certain neither of us hit it, as number one neither of us remember having done that, and number two you would think any hit hard enough to crack it we would have noticed. We thought of maybe the dog, but there again we feel like we would have heard it(he's only ever in the bed with us).

I looked around and couldn't find anything that would have hit it, but also don't know where it would have come from.

First of all, could something like this be caused from thermal expansion or the like? It's been hovering with highs in the 20s and and 30s the last few days, and this side does get morning sun, but that seems strange to me.

Second, I have a call in to a local glass shop to come look at it, but does anyone know if it might be possible to replace the pane without replacing the entire sash? It's a Reliance brand window that's probably not 4 years old (she bought the house in the fall of 2017, and things like the windows were fitted a few months before she bought it).

Also, can anyone suggest anything besides shrink wrapping to at least keep it insulated and contain glass until we do get this fixed? I'd like to avoid the old cardboard in the window look, but will if it's the only option.

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Show us a pic from ouside, at the point of origin. I'm wondering about a stray .22.

I can do so, but the outside pane is fine. Would a 22, or even something like a BB or Pellet, have hurt the outside pane rather than inside?
 
For containment, I have a roll of clear 2inch wide packing tape that would work great. Pretty cheap at hardware stores, or probably even Walmart.
 
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When we built our house we kept having a problem with one window cracking like that. The window company came out three times to replace it, the last time they decreased the overall size by a tiny amount which solved the problem. Here in Wisconsin we have larger temperature swings but for our window it was definitely the stress from expansion and contraction.

You can put clear contact paper on the pane or the self-adhesive plastic wrap that is used to contain breakage. Window places sell it.
 
I had the same thing happen to one of our windows this winter...it is 6'+ above our bed with no chance of bumping or hitting it. I just chalked it up to a thermal problem or house settling. The window still opens and closes just fine though...only the inner pane was broken.

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I can do so, but the outside pane is fine. Would a 22, or even something like a BB or Pellet, have hurt the outside pane rather than inside?
I think not, that is odd, I wonder if some moisture condensed in the right spot and froze, cracking it. Or just some weird thermal expansion.
 
How old is the house ? possible stress fracture from settling ?
1953. One thing that potentially does scare me is that we are on top of an abandoned coal mine per state geological survey maps. This exact area has no known mine subsidence, but it's a big problem just about 3 miles north, and I've read that for this general area it's not "if" but "when." I hope this isn't an indication of that.
 
Thanks also to everyone on the thermal expansion comments and that it COULD be an issue. I'm just stumped on it, and the cold temperatures were the only thing I could think of. It did start off about 20ª the night before and the sun warmed it up into the 40s pretty quickly.
 
Flaw in glass, stress from poor installation, temperature differential, house settling, all can contribute. Finding cause with CSI style investigation is of little help unless you think it has a warranty you can take advantage of.

You can't replace just the glass. It's a sealed unit, possibly exotic gas like argon, desiccant in the frame, made to be more efficient at insulation.
 
No problem! Glass shops will make you a whole new double pane assembly and replace the whole glass while keeping the original frame.
Something definitely impacted the edge of that glass though. It might be found once the pane is removed. It could just be from a very tight fit and a small movement. I hope it's not subsidence.
 
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Stress or possibly temperature extremes from inside and outside your home(?). I would put some shipping tape on the cracks and you can order a new thermopane and replace it yourself or have a window guy do it for you. My guess is stress and it could have had a defect behind the frame which you couldn't see. I had a large pane do that on my patio door window and the glass guy thought if was from the sun heating up the outside and the very low temperature I had my a/c set at affecting the inside glass.
 
Glass breaks some times it is stress from the frame heat cold vibration etc.. Who is the manufacture of the windows. The windows look newish.
 
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Is that the bed next to the window? if one of you has the 'Jimmy Legs' then the mystery might be solved?
I believe this is what happened. If you remember Frank and Estelle Costanza had separate beds because Estelle had the Jimmy Arm.
 
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