DASMA TDS 185 - Thermal Bowing in Insulated Garage Door Panels

A homeowner notices that the middle section of their insulated garage door bows outward on a sunny afternoon, then straightens out by evening. That is thermal bowing. DASMA TDS 185 explains the physics behind it and when it crosses the line from normal behavior to a real problem.

What this data sheet says

DASMA TDS 185 addresses thermal bowing, a deflection that occurs in garage door sections with bonded foam-core construction (sometimes called "sandwiched" sections). When the outer steel skin is exposed to direct sunlight or a large exterior-to-interior temperature difference, it expands faster than the inner skin. Because both skins are bonded to the foam core, neither skin can expand independently, so the section bends.

"Thermal bowing is a physical phenomenon that results from the differential thermal expansion of the two steel skins of a bonded-core garage door section."

The TDS makes clear that thermal bowing is not inherently a manufacturing defect. It is a predictable physical response. Manufacturers design bonded-core sections knowing this will occur to some degree under certain conditions.

Key factors that increase the magnitude of bowing:

• Dark exterior colors: darker finishes absorb more solar energy and reach higher surface temperatures.
• Wide sections: a 16-foot-wide door section has more length over which the deflection accumulates.
• Thin steel skins: lighter-gauge steel (thinner) is less stiff and deflects more for the same temperature delta.
• High solar gain days: direct afternoon sun at low angles creates the highest surface temperatures.

TDS 185 also defines when bowing becomes a functional problem: if the deflection is severe enough to bind the door in the track or create a persistent gap at the weatherseal, the cause needs investigation.

When it applies

Thermal bowing is especially visible in Colorado for two reasons:

First, Denver averages about 300 sunny days per year, and the Front Range receives intense direct sunlight at high altitude. A dark-painted door facing west can reach steel surface temperatures exceeding 140 degrees Fahrenheit on a summer afternoon, even when the air temperature is only 90 degrees.

Second, many Front Range homes were built in the 1980s and 1990s with vinyl-backed foam-core doors using relatively thin (25-gauge) steel. These doors bow more than modern 24-gauge or 25-gauge options with stiffened sections.

If the door straightens by evening and continues to operate normally, TDS 185 describes this as expected behavior. If the door binds, pulls a section out of track, or shows a permanent bow when temperatures equalize, that warrants a closer look.

What this means for you

Dark colors on south- or west-facing doors create the most visible bowing. If you are choosing a new door color and the door gets afternoon sun, a lighter or medium color reduces the temperature differential and reduces bowing magnitude.

Temporary bowing that self-corrects is not a warranty issue under most manufacturer policies, because TDS 185 classifies it as a normal physical phenomenon. Read your warranty terms to confirm, but this distinction is important before calling for a warranty claim.

Persistent bowing or binding after temperatures normalize is a different situation. It may indicate a damaged foam bond, a section that was hit, or a strut problem. Those conditions merit a service call.

G Brothers can assess whether a bowing door is within the normal thermal range or indicates a structural issue. We serve the Denver metro area and Front Range communities.

Full text and source

Download DASMA TDS 185 from the official TDS index at https://www.dasma.com/technical-data-sheets/.

This entry applies to residential and light commercial sectional garage doors with bonded foam-core panel construction. Non-insulated (non-bonded) doors do not experience the same bowing mechanism.