Is There an Impact Rated Glass Block Window?

Glass Block Window
What does ‘impact rated’ mean?


In recent years Florida has aggressively beefed up building codes. This is largely in response to devastating hurricane activity, and has improved the quality and integrity of our homes and commercial buildings. While we can appreciate the improvement, there is often confusion regarding who needs impact rated windows. In addition, the impact system for glass blocks is more than just a new product, it is a new method of installation. This means an additional learning curve for the installers. Very few people want to be on the beginning of someone’s learning curve!


What does the ‘impact test and impact windows‘ look like?


The large missile impact test must have been designed by a bunch of twelve year olds. First, you take a cannon. Next, you get a nine pound 2×4, stick it in the cannon, and shoot it at the window at 34 miles per hour. Sounds like a great job, shooting 2×4’s at windows all day! To pass the test and satisfy Miami Dade requirements (the most stringent in the state and acceptable state wide) there can be no penetration, which does not compromise the envelope of the house and the design pressures stay intact. In short, your roof, doors, and windows keep the wind and rain out. Your valuables stay dry and undisturbed!


How does glass block fare and impact windows?


Glass block installed using the impact system does not break, nor allow any wind to compromise the envelope of the house. The installation process is the key to its success. For starters, a block with a thicker face is used. This prevents shattering of the glass itself. In addition, there is no mortar used when installing glass blocks in accordance with impact requirements. A perimeter of channel (vinyl or aluminum) is installed. The glass block is installed in the channel using silicone, and vinyl spacers fill the voids between the blocks. Once constructed, the joints are filled with silicone, completing the seal. This silicone construction allows the 2×4 to bounce off of the window.


What’s so hard about that?


Mason’s typically work with mortar and trowels, not caulk guns and silicone. Working with silicone requires patience, and most importantly, experience. As I stated before, who wants to be on the front end of someone’s learning curve? Silicone improperly applied leaves smears on the glass, and, worse yet, a poor seal that lets water in. Make sure that your installer knows what he/she is doing, and has done this type of application before!


What about the cost?


You can expect to pay about 2-3 times more for an impact rated glass block window than a standard glass block window. This is consistent with the price difference between impact and non-impact windows, and, where the codes demand it, is just part of the cost of living on the coast!

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