Replies

1. 
   TommyB12 | Feb 15, 2003 05:23am | #1

   I'm not sure I can shed any light on the problem although I have a similar one with vinyl windows.

   We installed some rather large vinyl composite window units about two years ago on a commercial job.  They were maybe 6' wide picture units with transoms about 5' tall.  The transoms have almost all cracked in a manner similar to yours.  The window manufacturer questioned the framing but the headers were all oversized.   Somewhere along the way they suggested that the glass was made to big, and they have replaced multiple units but none of them more than once.  That leads me to believe that that was the problem.  I would expect a similar result with an aluminum window with oversized glass.

   Hope this helps.

   Tom

2. 
   MikeSmith | Feb 15, 2003 05:47pm | #2

   two things occur to me.... one.. did they have one of those films applied to the window ?...this will add a surface tension to the glass that will stress it to the point that any nick in the edge will run  and turn into a crack..

    the 2d is that one of the mouldings installed in your settin may have a nail that is in contact with the edge .. and that stress point has run and turned  into a crack..

   in either case the symptom sounds like edge stress 

   Mike Smith Rhode Island : Design / Build / Repair / Restore
1. 
   jimblodgett | Feb 15, 2003 07:15pm | #3

   Yeah, sounds like a knick in the edge of the glass that grew over time.  I've done this a few times, hand nailing a stop in, where the nail JUST touches the edge of the pane, I see it crack, then the crack disappears.  Sure enough, within a couple years, something vibrates the window enough for the crack to reappear and lengthen, like  the way a windshield crack grows, only in a straight line.  Odd that you had two on one job though, huh?

   That's another good reason to always order glass about 1/8" smaller each dimension than you need, and set it on spacer blocks or against double sided glazing tape.  The weak point is the edge - especially tempered glass.

1. 
   HHawkes | Feb 16, 2003 02:13am | #4

   Thank you for your reply.  I am going to the jobsite Tuesday with the window rep and I will check to see if there is any way we may have hit the glass with a nail.

1. 
   Robertzcool | Mar 01, 2003 06:10pm | #5

   On a large window another problem can be that the window was not set square and plum and resulted in the frame being "twisted".  This puts stress on the glass which eventually causing a crack.  An easy way to check this is to run string diagonaly across the unit in both directions.  The string should just barely touch in the center.

   Also what thickness of glass was used.  Make sure it was engineered to withstand the wind loads that that size unit will have to endure.