Afternoon Sun + "Low E Windows" may cause major damage to your property...
How a baffling mystery turned into an unexpected lesson in modern windows
By R. Dominique
A few months ago I was getting ready to install a new above-ground swimming pool. Like many people do, I purchased twelve 4-by-8-foot sheets of rigid foam insulation from Quinn Lumber in Macon. At roughly thirty dollars a sheet, the insulation represented a fairly substantial investment. My plan was to place the insulation between the pool liner and the carefully prepared, level base where the 8,400-gallon pool is now installed.
The stack of insulation remained in the yard for only a few days before something happened that completely baffled me. The top two sheets had literally melted. A long narrow groove had burned completely through the top sheet and badly damaged the sheet beneath it. The damage looked as though someone had laid a red-hot steel fence post across the stack. Another possibility crossed my mind. Had someone spilled some type of solvent onto the insulation? Nothing about the damage made any sense.
Frustrated, I called Quinn Lumber. My friend Chris, who works at Quinn's, patiently listened while I explained what had happened. He suggested that the damage had probably been caused by concentrated sunlight reflected from a nearby window, a vehicle windshield, a shiny metal sign, or some other reflective object. At the time, I wasn't convinced. It simply didn't seem possible that reflected sunlight could melt rigid foam insulation. One thing I did know was that I wasn't about to place an 8,400-gallon swimming pool on top of insulation that had mysteriously melted while sitting in my yard.
Without hesitation, Chris arranged for Quinn Lumber's delivery truck to come to my house. The crew loaded the remaining insulation and hauled it back to the lumber yard. Even though no one knew what had actually caused the damage, Quinn Lumber credited my card for the full purchase price. That level of customer service deserves to be recognized.
A few days later I spread the heavy plastic ground tarp supplied with the pool over the same prepared location. The next afternoon I discovered another surprise. The tarp had melted.
A strip nearly four inches wide and approximately six feet long had burned completely through the plastic. The damage appeared in almost the exact location where the insulation had previously been destroyed. Now I knew something very strange was happening.
The pool was eventually assembled anyway, and for a while I gave little more thought to the mystery. Then one hot afternoon I climbed into the water for a swim. As I moved toward one end of the pool, I suddenly found myself looking directly into an intense reflection of the afternoon sun coming from an upstairs window on the house. The glare was so bright and the heat was so intense that I instinctively turned my head away. I could actually feel the heat striking my face. It wasn't simply bright sunlight. It felt like standing in front of an open oven. I grabbed my handheld digital thermometer and it registered 185 F on the reflective window.
The upstairs window is a modern double-pane window with a Low-E coating. Decorative dividers inside the insulated glass create the appearance of six individual window panes. Standing in exactly the right position, I could clearly see six separate images of the sun reflected in the glass. The concentrated reflection was aimed directly at the spot where the insulation and later the pool tarp had been sitting. I covered the outside of the window with landscape shade cloth. The result was immediate. The reflected glare disappeared completely. So did the intense beam of light. It must be noted that the bedroom on the inside of this window was always super-hot on a sunny day.
The evidence now fit together remarkably well. Two different materials had been damaged in the same location on different days. The reflected beam could be seen with my own eyes and measured with my hand-held digital thermometer. Covering the window eliminated the reflection and the super heated bedroom condition.
While researching the subject afterward, I discovered that this phenomenon has been documented in many parts of the country. Under the right conditions, certain double-pane Low-E windows can reflect and concentrate enough solar energy to damage vinyl siding, artificial turf, dog houses, chicken coops, plastic furniture, and other heat-sensitive materials. Most homeowners never suspect a window because the damage often appears several yards away from the house.
If you've ever found unexplained melted plastic, warped siding, scorched landscaping or mysterious heat damage in your yard, don't immediately assume vandalism, inferior products or spilled chemicals. Spend a few minutes outside on a clear summer afternoon and watch where the reflected sunlight from your windows fall. Vehicle windshields also cause this phenomenon.
On Monday, I'll be stopping by Quinn Lumber to pay for the two damaged sheets of insulation.
The damaged insulation board wasn't the fault of Chris, and It wasn't the fault of Quinn Lumber or the insulation manufacturer. It was the result of a very unusual combination of modern Low-E coated double-pane windows and the geometry of reflected sunlight and an unobstructed summer sun over Macon, Missouri.
Regards Maconites,
R.Dominique - Editor
Very good information. I need to check my west facing windows