Mark Meshulam is an expert witness and consultant for windows, glass and building exteriors.
This is the very first posting of Chicago Window Expert… welcome!
Windows (the building kind, not the Bill Gates kind), have become an increasingly pivotal element of almost every building, whether new or existing.
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I have a rental home out of state (IL) with a approx. 7’x4′ fixed, insulated-glass, vinyl picture window. After an ice storm, my renters told me that a branch had fallen & cracked the glass in this window. I sent a friend (since I live in CA) to look at it. The glass on the INSIDE was cracked– outside glass was fine, & no marks or blemishes on the outside vinyl frame.
My question: Is it possible for an impact from the outside to crack the inside pane of this dual-pane window?
Or, if it’s possible, is it likely?
Thanks- Daryl Walker Walker Construction darylwalker1@comcast.net
Hi Daryl,
That’s a good one. Mental note: write an article on glass breakage patterns. It’s a cool subject.
To answer your question, yes it is possible for an outside impact to initiate the breakage of an interior lite.
I can think of these circumstances:
1. The inner and outer lite are different with regard to tempering. If the outer lite is tempered, it can absorb almost four times the blunt impact force (prior to breaking) than a non-tempered lite can tolerate. During the impact, it deflects and hits the interior non-tempered lite which is more brittle. Counter argument: the outer lite must travel the distance of the airspace before even touching the inboard lite. By this time it has already absorbed much of the blow. Then it must deflect the inner lite to the breaking point without itself breaking. Likelihood: low.
2. The inner lite has a concealed defect which is triggered by the outside impact. The most common defect which could behave this way is a chip in the edge of the glass (sometimes called an “oyster” but don’t eat it). It is concealed within the frame. Edge damage which eventually devolves into breakage usually expresses itself in the first few seasons, responding to thermal cycles, which your Illinois home should experience. It could be possible that an outside impact could get that edge chip to “run”. Likelihood: medium.
3. Tenant had wild party and drunk bimbo stumbled and put elbow into glass. Or jock buddy was trying out new 3-iron and missed the open part of the window. Have a security deposit?
Daryl, if you have pictures of the breakage pattern or the branch, send them to mmeshulam@buildersarch.com and I will be happy to comment further.
Thanks so much for your response. I have a cell phone picture but it’s not very clear. I’ll see if I can have someone take a better one & get back to you. I suspect your option #3 is the most realistic. Thanks again…
I have been looking looking around for this kind of information. Will you post some more in future? I’ll be grateful if you will.