The most common cause of these stress cracks is extreme temperature fluctuation.
How to detect cracks in window and door.
Check the exterior caulking around doors and windows and see whether exterior storm doors and primary doors seal tightly.
Inspect windows and doors for air leaks.
Hold a lit incense stick by windows outlets doors and any other suspected areas.
If smoke blows sideways you likely have a leak.
Stress cracks start off small and then expand and grow across the glass.
In most cases the crack will follow a curve in the shape of an hourglass.
The windows cannot withstand the pressure of these scenarios and will crack as a result.
Turn off the furnace and water heater and turn on exhaust fans.
You can usually find them near the edge of the window glass.
Stress cracks can form when there is a large difference between the temperatures inside and outside your home.
Doors and windows another way to test the seriousness of a wall crack is to open and close internal doors to bedrooms and bathrooms and evaluate whether the doors stick.