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NAHB Reports on Damage From Window Sunlight Reflection

While not necessarily a common occurrence, damage to vinyl siding from reflected sunlight reflected off low-e windows has been reported in all climate regions where the product is normally used.

A new report from NAHB’s Building Product Issues Committee describes the phenomenon, and suggests several approaches to keep reflected sunlight from distorting and melting vinyl siding on neighboring homes.

Double-paned, low-e windows may develop a concavity due to a difference in barometric pressure between the glass panes and the outside air, according to a mini-task force that was designated by the committee to investigate the issue. While the concavity does not affect window performance and is not considered a defect, it can focus reflected sunlight on nearby surfaces, including a neighbor’s vinyl siding, much like a magnifying glass.

The reflected sunlight can generate heat in excess of 200 degrees Fahrenheit, sufficient to distort vinyl siding. Other materials and components can be affected as well; there have been reports of reflected sunlight discoloring and charring wood and damaging paint, decking, window lineals and trim.

There appear to be a number of factors behind the phenomenon, including the angle of the sun and the time of year, separation distances, wind speed, air temperature and intervening foliage.

The NAHB report details several remedies, including:

  • Installing screens or awnings on the double-paned, low-e windows
  • Planting trees or shrubs to block the reflected sunlight
  • Using  double-paned, low-e windows equipped with capillary tubes to equalize barometric pressure
  • Using low-e windows with double-strength glass

Additionally , the vinyl siding industry is exploring the development of heat-resistant vinyl siding designed to withstand temperatures beyond 200 degrees.

To view the report, which has been posted in the Construction Liability section of the Building Product Issues Committee Web page at www.nahb.org, NAHB members can click here.

For more information on reflected sunlight from low-e windows and its effect on vinyl siding, e-mail David Crump at NAHB, or call him at 800-368-5242 x8491; or e-mail Matt Dobson at the Vinyl Siding Institute, or call him at 703-244-2930.

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