Understanding Concentrated Solar Reflection and Its Potential Damaging Effects

Cases of siding distortion (sometimes described as “melted” siding) caused by concentrated sunlight reflected from windows have been getting media attention. In every case, the evidence is overwhelming and unavoidable that multi-pane Low-e windows are capable of concentrating and reflecting solar energy sufficient to damage a wide variety of materials.

The key factor common to every case of damage is the unnatural concentration of solar energy in the reflection off the concave, lens-like surface that can occur in window glass under some conditions.

Damage to property caused by concentrated solar radiation reflecting off multi-pane Low-e windows is infrequent and occurs only under a unique set of conditions. Homeowners can protect their personal property in such instances by blocking the path of sunlight, either to the window or between the window and the siding. This includes the strategic placement of trees, bushes or other landscaping elements and the use of sunshades above windows. Screening applied to windows may reduce the total amount of reflected energy sufficiently to avoid the problem.

If you are a member of the media researching this topic, we encourage you to start with our “Open Letter to Journalists.”

Builders, remodelers, and architects: We’ve included links to white papers that provide technical information.

And all are welcomed and encouraged to watch a less technical illustration of the phenomenon in this short video (below).

View our questions about concentrated solar reflection or review the recent media coverage of damage caused by low-e windows.