This homeowner had engaged several contractors to examine the problem, but none of them could explain what was happening. She had the siding replaced, but it melted again (Photo 1). Her chimney guy simply told her not to use the fireplace.
During my visit, I saw melted siding on the exterior of a wood-framed and vinyl-sided chimney chase. Inside the chase was a factory-manufactured fireplace and metal flue.
Here Comes the Sun
Because the professional fireplace evaluation had found nothing wrong, I concluded that ultraviolet energy reflecting off the high-efficiency (low-emissive [low-E]) window melted the siding.
Take a look at the window next to the chase (Photo2). The window faces south. All day long, the sun reflects off the glass and onto the siding.
The owner had several options: Cover the window with an awning, install a screen, replace the glass with a new pane with nonreflective coating, or put up some type of shield or plant a bush to block the sun.
Although the owner was not happy about the continuing problem, she was relieved to hear these solutions for the melted vinyl.
Melted Siding Needs to be Reported
During your inspection, note any significant damage to siding of any type. Melted vinyl is found often next to the patio slab, which probably means that a barbeque flame next to the home got a little too hot.
Melted siding away from the patio is a different problem. You don’t need to identify the cause, but you should recommend further evaluation. I have also seen extensively damaged siding due to reflected energy from the neighbors’ windows (Photo3). There’s a pattern to this melting; maybe it follows the movement of the sun (Photo4).
Here is What’s Happening
What causes the issue? High-efficiency glass with low-E coating reflects the sun’s ultraviolet rays. Low-E glass protects the interior of the home and limits heat transfer, but under the right conditions, these properties can lead to damaged vinyl siding.
A secondary theory is that the glass is slightly convex. The space between the window layers is sealed, so changes in pressure outside the glass might bend it. This, in turn, may focus heat from the sun.
Tom Feiza has been a professional home inspector since 1992 and has a degree in engineering. Through HowToOperateYourHome.com, he provides high-quality marketing materials that help professional home inspectors educate their customers. Copyright © 2018 by Tom Feiza, Mr. Fix-It, Inc. Reproduced with permission.