AskMrRogers.com Home Improvement Questions? Ask Mr. Rogers

It is a crazy phenomenon, but windows can actually affect vinyl siding and create a meltdown, although it is pretty rare. I recently saw a news report about one incident that goes something like this: A homeowner’s vinyl siding is bowed, warped, and buckling—for the second time in two years—from sunlight reflected off the neighbor’s windows. And there are six other houses in the neighborhood with similar ‘melting’.

So let’s take a closer look at this phenomenon.

Warping vinyl siding has occurred before. In fact, the Vinyl Siding Institute (VSI) issued a warning about such distortion over 8 years ago. The Institute reported that a number of other variables can contribute to siding distortion:

• outdoor temperature and wind speed
• how close other heat sources are, such as air conditioning compressors
• color and solar absorption of the vinyl siding (darker colors absorb more heat)
• the heat distortion temperature of the vinyl siding (cheap siding has a low distortion temp)
• architectural designs that block wind and trap heat
• angle of the sun and orientation of the glass relative to the vinyl siding
• distance of the window to the vinyl siding

It’s usually a combination of one or more contributing factors that occur before the siding “melts”. Even home-builders are reluctant to blame the neighbor’s windows, and point to a variety of factors that could affect the intensity of the reflected sunlight.

Each case needs to be investigated on an individual basis.

For example, melting can occur from the reflection and radiant heat of a dark roof, or the pavement, or some underlayments. And crazy at it may seem, even an interior vapor barrier installed behind drywall can trap enough heat under the right conditions to affect siding. Alcoves that block the wind, overhangs that trap convected heat, and inside corners that capture glass reflections…these can all contribute to the problem.

A home inspector friend of mine agrees—there are other contributing factors that can cause vinyl siding to warp, buckle and melt. He’s observed it mostly in newer neighborhoods, where the homes are built really close to one another.

And it could be the quality of the siding.

According to current manufacturing standards, normal grade vinyl siding begins to distort at 160 – 165 degrees. That’s pretty low to begin with. Now consider that newer homes and retrofits have darker siding options—grays and beiges—which absorb considerably more heat than white siding when exposed to reflected or even direct sunlight.

Research from Cardinal Glass Industries shows that vinyl siding with high solar absorbency can distort from solar reflections from all glass products, including clear glass as well as glass with one or multiple Low-E coatings.

In my opinion, Low-E windows are not the problem.

Local building codes all over the country now require installation of energy-efficient windows with Low-E coatings. Low-E glass and energy-efficient construction make good sense for your home and for the environment. We’ve saved millions of dollars in energy because of these requirements, plus we substantially reduced greenhouse gas emissions from the lower energy consumption. Low-E windows are here to stay.

I think what’s happening is more indicative of the cheap, lower grade siding commonly used by tract builders. Maybe you’ve heard toe saying, “Cheap is the most expensive price to pay.” Wood and metal siding products, which cost more, react to reflected solar radiation at much higher temperatures. Inferior products just can’t be trusted to hold up under extreme conditions.

So what’s a homeowner to do? Choose siding with a high heat distortion rating, high solar reflectivity, and a light color. If you already have vinyl siding that may be affected by heat distortion, plant shrubbery or trees to deflect heat, and in some cases screens or awnings can help.

For more technical information about vinyl siding distortion, you can read the Cardinal IG technical bulletin here.

This entry was posted on Wednesday, March 3rd, 2010 at 2:37 pm and is filed under Case Histories, Energy Efficiency, Windows. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.