Vinyl Siding and Solar Distortion

If you have ever seen what looks like vinyl siding melting on the side of a home it is most likely solar distortion cause by concentrated sunlight reflected from energy efficient windows. The windows are concentrating and reflecting solar energy onto the siding and heating it to the point where it starts to distort.

I don't see this a lot but when I do it can be a significant visual impact on the the home. Most of the time it is the neighbor's windows that are the source.

A very narrow set of conditions needs to come together in order to cause the problem, and this happens very infrequently. If your house has not been affected in the past, it is not likely to be affected in the future. This can change, however, if windows are replaced (either on your home or your neighbor’s) with ones that are more likely to concentrate the sunlight, or if something that blocked sunlight is removed.

I have seen it cause by a window across the street so it is not possible to predict what distance is at greatest risk or whether there is a “safe” distance from the window. The range or of distance from the window in which the reflected beam is most concentrated depends mostly on the curvature of the glass. The curve can be different for different windows, and can even change in the same window under different temperature and atmospheric pressure conditions.

Anything that falls in the path of that reflected beam can be harmed including cups, bags, pool covers, car parts, painted surfaces, and cedar shingles are a few of the materials reported in the media to have been damaged.

The phenomenon can occur anywhere the sun shines, in any season. Even when the air is cool in winter, if the sun’s energy is concentrated onto a small surface area, that location can become far hotter than the surrounding area. But in many cases the relationships of the angle of the sun, the direction of the window and the location of the house wall are “just right” only at certain times of the year. But that's all it takes to do the damage.