Everything You Need to Know About Fire Rated Windows

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Before a window can be labeled “fire-rated”, they must first go through a series of strenuous testing to prove that they are able to hold in extreme temperatures. 

The first test is a heat test, where the windows are exposed to 1600 degree Fahrenheit for 20-90 minutes. This is used to ensure that the glass will prevent the spread of flames and smoke.  For normal tempered glass, the average heat test is held for 20 minutes.  Anything beyond that falls into specially tempered glass, which is much stronger.  The second test, followed immediately after the first, is a hose stream test.  Essentially, a powerful water hose is held to the still hot window to make sure that it is able to undergo extreme changes in the temperature without shattering or warping.  Only after passing these tests do the windows get the “fire-rated” windows.

There are three different types of fire-rated glass available in the market;  wired glass, specially tempered glass, and intumescent glass.


Wired glass is commonly found in schools and businesses.  It is a glass sheet that contains a wire mesh between the panes, preventing it from shattering or breakign when exposed to high temperatures.  Specially tempered glass has a higher fire rating that the 20 minutes that you typically find in tempered glass.  It can have a fire rating up to 90 minutes, more than 4x that of normal tempered glass.  Lastly, there is intumescent glass, which is the strongest you can buy.  What makes this glass so powerful is that it is made of an alternate layer of glass and laminate.  It offers the highest level of fire protection and is fire rated for 3 hours.

Case Study: 630 9th Avenue

630 9th Avenue, also known as Manhattan’s Film Center Building, is a landmarked commercial building located in the heart of Hell’s Kitchen. Last year  Adler Windows was brought onto the project by Shawmut Design and Construction. We worked with our manufacturer, Optimum Window, to supply and install over 100 fire-rated steel double hung windows, all with a 90 minute fire rating.  These new windows offer better safety and protection from any fires or exposure to extreme heat, giving those inside a stronger sense of security and safety.