horizontal crack in window above foyer

[PSUengineer1]

Please reference attached photographs, thank you. I am looking to gather information in regard to a two-story, double-paned foyer window with interior ledge above a front entry door that displays a horizontal crack in one of the windows and some fogging between the panes in another window. I am comfortable with the cause of the fogging between the panes. I am more interested in gathering information on the horizontal crack of one of the windows. The window appears to have possibly been installed out of plumb based on the lack of apparent tearing displayed in the vertical beads of caulk between the brick veneer and the window frame. The window was installed in 1992. I am trying to gather information to research so as to come up with a conclusion in regard to the reason for the crack in the window. The crack was noticed in early spring 2014 following one of the fiercest winters in recent history (polar vortex; northeastern portion of U.S.). The unit is leaning inward, toward the home’s interior as was measured with a 4-foot digital level.

 

[jayrod12]

I'd be tempted to say that the window pane itself was too strictly constrained at it's edges and didn't allow for the proper thermal shrinkage. Manufactured in a warm plant, installed and operated in mostly warm temperatures, then a whopper of a cold winter hits and the pane isn't allowed to shrink so it cracks.

That's just my first thought considering none of the other panes appeared to show signs of movement that could cause a pane to crack like that.

 

[msquared48]

Is it just my eyes, or is the lower window horizontal mullion, just above the affected panes, bowing in.

I wonder if the mullion system is improperly framed allowing too much lateral deflection too.

Mike McCann, PE, SE (WA)

 

[dhengr]

Jimjxs263:
The right edge of the broken window is pretty well held straight by the right jamb, caulking, brick and wood framed pier. I also think MikeMc’s eye is also pretty good in terms of the mullion below this window moving. That window was twisted out of plane by this middle jamb and mullion movement. For example, twisting the top of that broken window clockwise and the bottom counter clockwise about its own plane. Then, there was probably some form of stress raiser along the vert. edge of the glass and it broke. The same thing, to a lesser extent, happened with the lower middle window because its lower edge is kinda restrained and the max. deflection happened at its upper right corner; at least enough to break the seal. That window arrangement, its jambs and mullions, is probably not framed properly for that shape and size of opening, and this should be studied. You might be better off having the mullions continuous, from side to side, and the jambs spanning btwn. the mullions.

 

[DBronson]

jimjxs263:

My feeling is that the proximate cause of the breakage is edge damage on that unit. The crack pattern doesn't look like a thermal crack. Unfortunately without removing the unit from its frame it's just about impossible to tell for sure. The plumbness of the widow is irrelevant to the cracking. Bear in mind the units are 22 years old. Judging by the amount of damage to the adjacent finishes the seal failure on the other unit looks like it occurred several years ago. The unit immediately above it looks suspect as well. My recommendation is to consult with the glass unit manufacturer and get their input. (Their name is usually stamped on the metal spacer separating the glass lights.)

Regards,

DB