The magnitude of thermal stress depends on the temperature difference between the hottest and coldest parts of the glass and also on the distribution of the temperature across the glass. Glass is commonly glazed by retaining the edges of the glass with a gasket or glazing bead. The area of glass exposed to solar radiation absorbs heat, rises in temperature and expands. The edges of the glass, which are shielded from solar radiation, remain cooler than the exposed area. The resulting differential expansion causes tensile stress at the edge of the glass, if this exceeds the breakage strength of the glass a thermal fracture will result.

The risk of thermal fracture of glass can be assessed for Pilkington products using the Pilkington Thermal Stress online calculator which is available in our MyPilkington online resource. To register for MyPilkington, please click here.

If your glass has fractured, you should report this to the installer.  The glass may or may not have been manufactured by Pilkington; if it is of Pilkington origin, it may have been processed and fabricated into an insulating glass unit by a third party.