Fact or fiction: melted vinyl siding

Here's an instance of "truth is stranger than fiction": sometimes, the vinyl siding on houses has melted straight off the wall. Considering that vinyl siding doesn't lose its rigidity until temperatures reach 160 degrees and that air temperatures never reach 160 degrees in the United States, what's happening?

Windows get the blame on this one. Windows with a reflective coating such as that found in low-e glass can bounce light, and when concentrated to a point (which can happen when the pressure is high and the window glass forms a concave shape) it can create heat well in excess of 160 degrees.

It does not, however, happen every time the sun shines. Otherwise you'd see vinyl siding melting off on every warm day. The azimuth of the sun has to be at the exact angle to create the condition, which only happens a few days out of the year as the sun moves north in the spring and summer and south in the fall and winter.

Can the condition be totally eliminated? Not really, but there are a few solutions that can prevent the intense concentration of the light.

• Full screens on the windows covering the entire surface of the glass (no half screens) can diffuse the light.
• Double strength glass as opposed to single strength is not as radically impacted by changes in pressure.
• Use of non-low-e glass in the windows facing other houses will not reflect heat as efficiently. However, elimination of low-e glass can harm the Energy Star status of the home, so make sure doing this won't lower your energy savings.
• Use capillary tubes. Capillary tubes are used in insulated glass (two panes of glass with a gas filling the space between them) when transporting windows across altitudes such as the Rocky Mountains. The air space is kept open by inserting these small diameter tubes between the panes. When the windows reach altitude, the tubes are pinched closed at the ambient air pressure. Keeping the tubes open more quickly negates changes in barometric pressure, but can allow moisture migration into the insulated glass space causing internal condensation. Non-closure of capillary tubes also voids glass warranties, so use them at your own risk.

This likely won't be a problem you have to deal with often, and you may indeed never have an issue with it, but it's better to be safe than sorry. When you're having your windows replaced, ask your window contractor how you can prevent damaging nearby vinyl siding.