Window problems

selfbuilder2009

Hi all
I currently have a problem with cracked double glazing. I am not sure why it happened but my window company is suggesting thermal stress.
Has anybody heard about or experienced this problem before??
I am not sure what to do or how to get an independent evaluation of the remaining windows.

Selfbuilder2009

starbelgrade

When an inner pane in a sealed unit is the one to suffer breakage, this happens when the inner glass is warmed from the heating in the home, and the outer pane of a double glazed sealed unit is cold from a drop in outside temperatures. When an outer pane is the one to suffer breakage this happens when a cold outer pane is warmed quickly by the Sunlight bearing on it. The pane of glass subjected to the thermal stress cannot cope beyond a certain amount of deflection, and it will suddenly crack along the whole length of the unit, always along the long length, or it can suddenly shatter altogether.

Other contributing factors to double glazed sealed units breaking in this way can be:
(1) Very high atmospheric pressure at the time and
(2) An 'as manufactured' original high inbuilt negative pressure within the sealed unit.
(3) One sealed unit laboratory recreated the effect of the glass surface tension being damaged by being scratched when the lead/coloured film/bevels were being cut around with a blade. If the glass is scratched in this way during manufacture it can be a weak point when the glass is under stress and deflection.


If, when the double glazing sealed unit is actually sealed, it is during a period of low atmospheric pressure and high ambient temperature, then, during a cold snap when the external atmospheric pressure is high, the relative pressure inside the sealed unit will lower, producing a greater negative pressure within the sealed unit, and more inward deflection. This is why sealed units tend to suffer from the problem of implosion during mid Winter, when the differential is at it's greatest.

The more humid the air at the time of manufacture of the double glazing sealed unit, the more moisture is held in the air that is sealed up within the cavity of the sealed unit. When the edge seal is complete and the desiccant does it's job and absorbs the moisture, this will be yet another factor that would add to the decrease in internal pressure with the cavity of the sealed unit.

If a sealed unit was made up of one pane of 4mm glass and one of 6mm (thicker than normal) glass, then the one pane of 4mm glass would be more flexible and therefore suffer greater deflection and be more at risk of implosion than if both panes were 4mm (normal).

The actual breakage of a double glazed sealed unit often occurs due to thermal stress:

Both panes of a double glazed sealed unit experience thermally induced stresses, and when either an inner or outer pane breaks this is caused by the same conditions.
If you have a recurring problem with sealed units imploding then I would suggest
(1) Enquire if the sealed unit manufacturer understands what low deflection desiccant is, and do they use it, or feel that they should be using it,
(2) Consider having the replacement unit made of thicker glass, i.e. both panes of 6mm glass instead of the normal 4mm,
(3) Think about your room heating cycles, and
(4) How close the main curtains are to the window, and if air can circulate behind them.

frag4

what could happen also is if a wrong sized glass packers are used.

A 24mm unit needs a 28mm packer as a 24mm or less packer can slip behind the edge of one of the panes(outside one if external glazed, inside one if internal glazed) and cause a break when the sun comes out.

Glass could be measured tight and hitting reinforcing screws if it is a pvc window.

selfbuilder2009

Thanks Starbelgrade and frag4 for this information.

I have 2 X 6.4mm laminate double glazed units.

out | | | | | | inside
side | | |__| | |
1 2 3 4

The crack is on the inside pane of laminate glass on glass pane 3.
1 and 2 are the outside pane of glass.

I have this problem on 2 windows. Is this a common thing in Ireland?
I have never heard of this before and there does not seem to be any posts on this issue in this forum.

Thanks...