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RE: Glass Cracking

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Jesse and Jeff,

Jesse, I don't know if the glass is encapsulated (sealed) with gas between 
the two panes.  I think that it is just a double pane window with the panes 
separated by a gasket, at least that is what it looks like.

Jeff, the perplexing (to me) part of the crack is the parabolic shape.  If 
there was racking, I would expect the crack to be diagonal, e.g., failed in 
diagonal tension, a la concrete shear cracking.  I also don't know if there 
is a laminate applied to either pane.  The upstairs window is about 3' wide 
and 4' high; the first floor window is about 4'wide and 5' high.

There are workmanship problems regarding windows in the house.  The bottom 
sliding sash of a double hung window in a bedroom had fallen out of its frame 
and has been replaced but there is still an indication that the jamb is not 
plumb in that window --- a wider side gap at the top of the moveable sash 
than at the bottom.

The homeowners, who are not the original owners, fortunately were able to 
obtain copies of the county's approved plans just before the plans were 
scheduled for destruction and are trying to get additional information on the 
construction of the house.  I have made only an initial inspection of the 
house and don't know how far the homeowners want me to go with the 
investigation, or even if they want me to continue with an investigation.  If 
I do continue, your comments will be considered.

Thanks for your comments, an I welcome any other thoughts, comments, or 
suggestions from the knowledgeable people on this list.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Jesse D. Moore wrote:

. > Could it be gas expansion between the panes?

and Jeff Smith wrote:

. > How big are the window and are the headers supporting floor and roof load,
. > are there point loads over the windows? Any recent impact loads? You said 
. > no signs of distress, maybe do a water level survey, check all doors 
. > windows and cabinets for square/plumb. when was the house last painted has
. > there ever been any leaking i.e. shrink swell cycles? You may need to 
. > remove the trim to see how it was installed. Check for equal diagonals of 
. > the window opening for racking. I am sure you have thought of numerous
. > possibilities:

. > header deflection
. > wood shrinkage
. > maybe they were installed too tight with no shim space for the rough
. > opening.
. > some windows have receiving channels for deflection space and racking

. > Jeff

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