Tom Shafer

Inner strength makes vinyl windows a contender

June 13, 2011

If you've been told that vinyl windows are inferior to wood or aluminum windows, you've been mislead with outdated information. Today's vinyl windows are strong and energy-efficient--a worthy adversary of materials that have been around longer.

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When vinyl windows were first introduced in the U.S., frame material consisted of hollow vinyl extrusions -- also known as lineals -- with either a single chamber or a single chamber divided into two parts. It's true that these early vinyl windows had some issues. The single-chamber construction created a convection current, moving colder air to the warmer wall of the window frame and--just like an aluminum frame--creating condensation and a cold indoor window frame.

Condensation forms on windows

Condensation forms from convection current - credit http://chicagowindowexpert.com/2010/12/09/top-10-causes-of-window-condensation/

The single-chamber design also lacked structural strength. It bowed when pushed by the wind, causing both air and water leakage.

Multiple chambers revolutionized vinyl windows

Times have changed and vinyl lineals are now constructed with multiple chambers, making them structurally sound and energy-efficient.

  1. The internal web of multiple chambers is stronger than a single hollow chamber in much the same way the vertical member of a steel "I" beam makes the beam less likely to bend than a single bar of steel. Multiple-chamber lineals can withstand more wind pressure.
  2. The chambers prevent convection currents from forming condensation by blocking air movement, keeping colder outside air outside and warmer inside air inside.
  3. Air trapped in the chambers acts as an insulator, improving thermal performance.

Vinyl window frame cutaway

Multiple chambers give vinyl windows their inner strength - credit http://yoursunnyhouse.com/appearance_and_material_selection_windows_ct.html

Other design advancements over the years have further improved the strength of vinyl windows. Welding the corners of the frame and shaping the extrusions to allow for steel inserts both provide additional support and increased wind resistance, enough to allow mulling (combining a series of windows into one large window without brick or siding in between for added strength.)

Don't pay attention to anyone who tries to tell you vinyl replacement windows can't cut it. Vinyl is definitely one tough contender.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.


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