08/01/2009

The Impact of Impact-Resistant Windows

 

Major code changes have been enacted in recent years in response to hurricane damage requiring building envelopes to be more weatherproof and impact resistant. In fact, the damaging effects of gusting winds and windborne debris have been so widely documented that the entire Atlantic Coast has been declared a hurricane-prone region.

In the aftermath of Hurricane Andrew in 1992, South Florida adopted the first hurricane-resistant building codes and standards. What is less known is that the first code was actually based upon lessons learned from Cyclone Tracy, which hit Darwin, Australia, in 1974.

Engineering studies following the Darwin devastation found that the vast majority of the damage was caused by windborne debris and fluctuating pressures. Experts concluded that the single-gust concept of design was inadequate to protect against sustained, turbulent winds that change direction slowly and carry debris.

Lessons Learned: The Code Works

Yes, impact-resistant window systems work; however, the codes mandating such systems also aid with insurance and sales issues (thanks to Hurricane Wilma).

In 2005, Hurricane Wilma damaged many South Florida buildings built before impact-resistant codes (to the cost of $20.6 billion). While insurance claims are still pending for pre-code buildings, others built with the new code suffered little.

With clear evidence of the code’s success, Florida recently passed a statute requiring any condominium greater than 3 stories tall be inspected every 5 years to provide a report under seal of an architect or engineer.

The benefit? In case of storm damage, you’ll have a certified report stating that your facility was maintained to code, which should expedite insurance claim payments. Also, the report could be used in the sales process to erase doubts about the building’s health or pending audits for maintenance. With little surprise to the buyer, the sales process could also be expedited in a tough market. Other coastal states may follow suit on this statute.

Based upon these findings, new codes and test methods were developed with the intention of reducing the damage caused by hurricane winds and flying debris. The original test standards or protocols, TAS 201, 202, and 203, were developed by the state of Florida. Subsequently, ASTM developed two standards, E1886 and E1996, which have been adopted by the American Society of Civil Engineers (ASCE) and the Intl. Building Code (IBC).

ASCE 7 defines hurricane-prone regions and windborne-debris regions. Only buildings constructed in designated windborne-debris regions are required to have impact-resistant glazing to prevent wind from entering the structure (termed “internal pressurization”) or be designed to withstand increased loads resulting from internal pressurization. And, the code has been proven to work (see Lessons Learned: The Code Works, on the right).

For a glazing product to qualify as impact resistant, it must be demonstrated through testing that the assembled system meets the requirements of the standards:

  1. Impact with projectiles representing windborne debris – either large missile (projectile is a 9-pound, 2x4 timber) for systems in the lower 30 feet of a building, or small missile (projectiles are 10 2-gram steel balls) for systems 30 feet and above.
  2. Followed by cyclic structural loading (9,000 positive and negative static pressure loads) representing fluctuating wind pressures.

Products are qualified based upon the ability of three test specimens to resist large- or small-missile impacts, or both, without penetrating the inner plane of the glazing infill, and resist the cyclic pressure loading with no tear longer than 5 inches and wider than 116 inches through which air can pass. Test reports or product approval documents indicate a description of the test specimen and components, the maximum size, the pressure rating, and type of impact for which the product is approved.

Common glazing materials include traditional PVC laminated glass for small-missile impact-resistant systems, and PET laminated glass and glass-clad polycarbonate for large-missile impact-resistant systems. In almost all cases, the glazing is attached to the frame using structural silicone sealant.

Finally, it’s not always practical or economical for existing window/wall frames to be retrofitted and be certified as impact resistant. Rather, it’s far more cost effective to replace the entire unit with pre-tested, rated, and approved systems.

Mark Baker is president at Boca Raton, FL-based IBA Consultants Inc.. He can be reached at mbaker@ibaconsultants.com or at (888) 550-4422.

 


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Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

Replace core drilling with Connectrac In-Carpet and On-Floor Wireways, the proven connectivity solution in open interior spaces of all kinds. These elegant low-profile wireways are great for AV / telecom connectivity wherever it’s needed.

Bluebeam® Revu® simplifies digital facilities document management from design review to leveraging as-builts, maintenance manuals and O&Ms submittals.


 
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