Impact windows

Home Inspector with Home Inspector/Structural Engineer/Mold Assessor


Looking into Impact Rated Windows

          In new construction and renovation projects, growing numbers of builders and homeowners are electing to install impact rated windows.  High quality impact windows eliminate the need for storm shutters, serve as a noise barrier, prevent criminal break-ins, and may increase energy efficiency.  

Unfortunately, people throw around the term impact rated without truly understanding it.  To make sure you are getting the real McCoy from manufacturers or builders, read on.

Impact-rated windows are like the front windshield of your car; they are comprised of two layers of glass bonded together with a thin, clear interlayer of film or resin.  Windows certified as "impact-rated" must pass the Florida Building Code (FBC) test for either the "large" or "small" missile impact, AND survive a lengthy sequence of cyclical pressure testing.  Impact-rated windows also must also conform to the Code of Federal Regulations (CFR) for consumer product safety, the testing requirements of the American National Standards Institute (ANSI), and the guidelines from the Safety Glazing Certification Council (SGCC).

To achieve the "large" missile rating in Florida, three different windows of the same design are each shot with, and must survive two head-on impacts from, a nine pound, 2"x4" wooden timber traveling at 34 miles per hour.  Even though the glass may be shattered by the impact, the strong, interlayer of film absorbs the impact and keeps all the broken pieces together so neither wind nor water are able to pass through after it is hit.  The "small" missile rating is a lower rating of strength and requires each test window to survive three impacts; using ten 0.07 ounce steel balls with a diameter of 5/16" traveling at 88 miles per hour.  The windows must then pass a sequence of tests in which 9,000 various pressures cycles are applied to the inside and outside of the window to simulate the brutal cyclical forces of wind that occur during a storm. 

          To receive either the large or the small impact rating, the entire window assembly from the manufacturer must be equal to or greater than the strength of the glass itself.  The standard thickness of the glass in an impact-rated window is 5/16", which typically includes two pieces of glass each 1/8" thick, bonded with an interlayer material, such as PolyVinyl Butral, which is 0.03" thick.   The  attachment of  the frame to the wall of a structure must be equally strong.           

Impact rated windows should have a permanently etched label in one corner that shows four lines of data: (1) the manufacturer's name,  (2) "16 CFR 1201- I", (3) "ANSI Z97.1-2004", and (4) "SGCC Certified Product #" (e.g. 4444SUB).  However, those national standards are not enough to verify compliance with the Florida Building Code for your area since none require Florida's large or small missile tests.   

 The manufacture and/or installer of windows that are FBC missile tested and certified need to provide a homeowner with a separate label or certificate to that effect.  If you are claiming or required to install windows of a particular impact strength rating, your local municipal building inspector will need to see the certificate for final approval.  Be sure to receive and permanently retain any such certificates, receipts, and installation information.  All home buyers need to request and receive relevant documents and certificates from a seller prior to closing.

Like most modern technologies, impact windows are expensive.  However, they can save the cost of installing storm shutters, and may save energy.  Additionally, they provide 24/7 protection from storms and burglars without the need for shutters or bars.  No human can break through an impact rated window.

           On a final note, to ensure savings on your wind insurance, ALL your windows and doors must be equally rated against impacts (small or large). So, if you install impact windows in only certain rooms, all the other windows and doors in your home must have an equally rated protection barrier such as metal storm panels for full insurance savings.  Also, the "protective" films that some companies sell for homeowners to apply to windows are not sufficient, and no insurance companies recognize or give credit for their use.              


Greg Bertaux is a licensed professional engineer and home inspector.  His company, ISLE   Management Corp., provides property inspection services along the entire Treasure Coast. For more information call (772) 569-2141, or visit

Copyright 2008 ISLE Management Corporation


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