Thermal Bowing

Thermal bowing is the warping of an insulated steel garage door section. It happens when the outer and inner steel skins are at very different temperatures. The colder skin contracts more than the warm skin. Both skins are bonded to the same foam core and cannot slide. So the section curves, bowing out on the cooler face.

The effect is strongest in cold climates with sunny winter days. A dark door face can warm up fast when the sun hits it in the morning. The inside of the garage may still be near freezing. The outer skin tries to expand while the inner skin stays contracted. That difference in size pushes the section into a bow.

Signs of thermal bowing:

• The center of a section bows out while the corners stay in line with the sections above and below.
• The bow goes away as the temperatures even out during the day.
• Doors with polyurethane cores are more likely to bow than polystyrene-core doors. Polyurethane bonds tighter to both skins and allows less movement.

DASMA Technical Data Sheet TDS-185 covers thermal bowing in bonded-core sections. It gives guidance on testing and limits. Manufacturers may use thermal breaks between skins, floating skin systems, or foam types that allow small amounts of controlled movement.

Thermal bowing is not a structural failure. The door usually returns to flat when the temperature difference disappears. But a badly bowed section can drag on nearby sections, bind in the track, or leave a gap at the stop molding on one side. A section that stays bowed after temperatures equalize should be replaced.

A single-skin pan door cannot thermally bow. It has only one steel face and no insulation to create a differential.