Melting Vinyl Siding

In the past several years there has been a rather unique situation arise and that is melting siding as a result of the sun’s energy reflecting off of high performance Low-e glass windows.  If you read my post on how low-e glass works it might not be intuitive on why this phenomenon has happened.

When insulated glass is manufactured the glass is cleaned and then sandwiched between a glass spacer system.  This creates a dead air space between the glass panes, which creates an insulative space to resist heat.  The glass is sealed in the factory which locks in place a finite amount of air (or Argon gas) within the unit.  At the time of manufacture, the unit has more or less air/gas in the unit depending on the ambient atmospheric pressure.  On a hot summer day, less air is sealed in-between the glass than on a cold winter day.  What this means is that if the current outside atmospheric pressure in which the window is installed is greater than the pressure at the time of manufacture, then the glass will “bow” towards the interior of the insulated glass unit.  When this happens a concave glass surface acts like a parabolic mirror (or magnifying glass), as a result of the reflection created by the high performance Low-e.

The glass company scientists are studying this phenomenon right now; even they don’t have a complete understanding of the process.  What we all know is that the energy of the sun is concentrated by this parabolic mirror effect as it reflects off the glass. If the focal point hits the siding at precisely the right distance, then thin-walled vinyl siding can reach it’s distortion temperature and “melt”.  It doesn’t actually melt, it distorts.

Because of the large efficiency gains as a result of low-e glass, it looks like it is here to stay.  A few ways to combat this problem are:

  • Install full screen or solar screens to dissipate the light beam
  • Plant shrubs to block the light beams
  • Install awnings to block the sun
  • If it is a new home, design the southern exposure with deeper soffits to block the sun.

The solution is not to replace the high performance glass with clear low performance glass: that would be like rejecting the new automotive electric technology because it’s new and we like the “good ol’ days”.

BTW, there is a sale on buggy whips, if anybodies interested send your pony express communication, I’ll be on the porch with my hand fan–wish I had some ice!!!

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