California failure analysis lab was asked to determine why windows in an expensive hilltop home failed. The windows in question were Lo- E windows that were tinted to absorb infra-red light. At this location two south facing, side-by-side windows cracked. The window expert at Read Consulting was asked to perform a glass failure analysis to determine the root cause of the failure. For this failure analysis the site of the origin was cut from the window and the failure origin was examined using a low power optical microscope. Both windows failed in an identical manner. Thermal expansion of the center of the Low-E window put the ground glass window edges in tension.A damage site from either the window sizing or window seaming processes was activated by the thermally generated stresses and cracked these windows. Please refer to the photographs above.