By William D. Smith
As we approach another hurricane season, one that the prognosticators tell us will be very active, building owners on the eastern seaboard and the Gulf coast states will begin to think about preparedness. Not only will the weather experts issue words of caution, but manufacturers of building products will also bombard the airwaves with marketing campaigns designed to garner our attention and make us question the vulnerabilities of our homes and offices.
Many of us remember previous hurricanes where catastrophic damages made headlines and captured the nation’s attention. Often, these damages laid a foundation for significant building code revisions (Click here for a more in-depth post on this topic by Paul Beers.), but many property owners have procrastinated for far too long, and their property remains vulnerable to damage. If past experience is any kind of teacher, glazed assemblies like commercial storefront and curtain wall, as well as residential windows and doors, can be the cause of significant property damage.
The building codes that are written to protect us generally require that the exterior building envelope be structurally adequate and weather-resistant, and they require that windows and glazing systems be tested to demonstrate compliance. However, these issues are not always crystal clear. For example, the codes use terms such as weather-resistant, not weatherproof, so what expectations are realistic? Similarly, does testing and approval of windows and glazing systems for use in hurricane prone regions mean that they are hurricane proof? And when a manufacturer markets their product as a “hurricane window,” what does this mean?
History tells us that as the general knowledge base of hurricane events has broadened, building codes have evolved and the construction industry has responded. For example, resistance to failure because of flying debris has resulted in many manufacturers offering new impact-resistant glazing assemblies and wall systems. The development of more accurate and realistic methods to calculate wind speed has resulted in manufacturers providing products with far greater structural capacity. These two critical issues, impact resistance and structural wind load capacity, are those that most manufacturers point to when discussing “hurricane windows.”
However, water leakage during a hurricane is another item of concern. Without question, water leakage has been reported during previous hurricane events. Some of this was allegedly attributable to the windows, and in some cases these were newer “hurricane windows. ” So, is a hurricane window supposed to be waterproof?
At the risk of oversimplifying, certification of windows and glazing systems requires laboratory testing according to nationally recognized standards to evaluate a number of performance factors. One of these factors is resistance to water leakage. This test involves spraying water on the outside of the window while simultaneously applying wind pressure to simulate the effects of a wind driven rain. The variable in this test is not the volume of water applied, but the amount of wind pressure. The standards require that the wind pressure used during water testing is to be 15 percent of the pressure that is used to certify the product for wind load resistance. For example, if a manufacturer wants to sell their products for use in buildings where the maximum required wind load is 60 p.s.f., then the standards require that this same assembly be tested for resistance to water leakage at 15 percent of that pressure or 9 p.s.f.
Why the apparent disparity? Well, that could be the subject of another entire article, but things such as sustained vs. gust wind speeds, testing methodology, and product design are among the factors that are argued. Also, it must be remembered that conversion of wind speed to pressure is not a straight-line ratio, as some would expect. For example, 60 p.s.f. is an approximately 153 MPH wind speed, but 9 p.s.f. is approximately 59 MPH or roughly 38 percent of the higher speed, not 15 percent.
It must also be understood that the majority of the glazing systems and windows on the market cannot be designed to stop water, but instead must control the water that enters into them. This is especially true of operable windows and doors since they have hinged or sliding panels that, in order to function, cannot be permanently sealed in place. Instead, these products must use various types of weather-strips and gaskets to seal the operable panels, but these are water resistant, not waterproof. Even many inoperable fixed glass systems function this way also since they too use gaskets to seal the glass in place. Therefore, because water will pass inward of the gaskets and weather-strips and enter into the frame, the frame must be designed to control that water and eventually drain it back to the building exterior.
Again at the risk of oversimplifying, the water resistance capabilities of many glazed assemblies can be calculated in simplest terms by determining water column height, which is a calculation of how high water can rise when subjected to pressure. In our earlier example, water resistance testing at a pressure of 9 p.s.f. creates a water column of 1.73” so if the product is a sliding glass door for example, the manufacturer must design the frame in a manner that is able to contain at least that much water without overflowing.
Questions occasionally arise about the validity of the current requirements for water testing as stated in the standards, especially following a major hurricane. Some suggest that water testing should be done at more than 15 percent of the pressure that is used to certify the product for wind load resistance. Others argue that, even if the product is designed to accommodate it, no water should be allowed to pass inward of the gaskets or weather-strips. In the extreme, there are those who believe there should be no reduction allowed and that water testing should be done at the required design load pressure. Although we’re certainly not condoning such extremes, there are products on the market that are capable of water resistance at much higher pressures than the minimums required by the standards, and sometimes GCI does advocate the use of these products for certain building projects.
The evolution of the building codes means that new structures and remodeling projects in hurricane prone regions gain the benefit of improved construction materials and enhanced performance. Changes that have occurred in glazing systems and windows will provide increased energy savings, improved safety and greater resistance to wind pressures, water leakage and air leakage. However, some products are marketed as “hurricane windows,” and this undefined term should not be misconstrued to mean the windows are “hurricane proof.” Although windows that comply with the requirements of hurricane prone regions do provide enhanced performance, there are limitations, including resistance to water leakage. Therefore, we recommend that the available options be explored before making a final commitment, and that the limitations of these products be clearly understood.
William D. Smith is the President of Glazing Consultants International, LLC (GCI), a building envelope consulting firm in business since 1988. He has nearly 40 years of experience in the design and construction of glazing systems and building envelopes and is recognized as an expert in the field of windows, doors, glass, and exterior wall systems, including all aspects of weatherproofing and water intrusion. He is an authority on Exterior Insulation Finish Systems (EIFS), sealants, and waterproofing systems, and has an extensive history of forensic building investigation. Mr. Smith has demonstrated his expertise in the field of hurricane damage and development of hurricane protection systems. He has performed many post-hurricane damage investigations. Mr. Smith has designed a variety of glazing applications for new construction projects including windows, doors and glazed curtain walls as well as specialty glazing system for exhibits and blast resistance. Will can be reached at firstname.lastname@example.org or on Twitter @glazingconsult. Find out more about GCI on the web at http://www.glazingconsultants.com, and join its Building Envelope Matters LinkedIn group to discuss building envelope issues.