Hurricane Windows: Fact or Fiction?

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 wsmith@glazingconsultants.com 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.

Interior Air Seals: The Added Benefit

By William D. Smith 

In a prior column we discussed the importance of using flashing at openings and how the failure to do so can result in significant building damage.  This month we’ll look at another commonly overlooked weathering component for many different types of glazing systems, the interior air seal.

As the name implies, the interior air seal simply describes a seal or barrier installed around the interior perimeter of a fenestration product.  Traditionally, installation instructions published by many residential window manufacturers have required that insulation be placed between the window frame and the rough opening, but now, many manufacturers of both residential and commercial glazing products also recommend the use of expansion foam or an elastomeric sealant with backer rod. 

One benefit of an interior air seal is obvious; while insulation will obviously provide insulating value, an air seal around the inside of a window or door frame will help control air leakage.  But there’s a potential side benefit offered by the air seal that is often overlooked; water leakage prevention.  On the surface, it doesn’t seem like an interior “air seal” would have anything to do with controlling water leakage, so to understand how this works, we need to go back to basics. 

For water leakage to occur, three things are needed; 1) water, 2) a hole or breach for the water to penetrate and 3), a force to move the water through the hole.  Of these three, the volume of water is not a very significant factor.  To illustrate, imagine you’re holding a garden hose in a U shape and the hose is nearly filled with water as shown at right.  If you force air into one end of the hose as illustrated by the arrow, we all understand that the water will rise upward on the other end of the hose.  In fact, the laws of physics tell us that if we apply a pressure of approximately 5 pounds per square foot, the water will rise up the other end of the hose about 1 inch.  And it’s easy to understand that the greater the pressure, the higher the water will rise.  Now, if instead of a garden hose you were to use an equal length of fire hose, which clearly has a significantly greater volume of water, the physics remains the same: a pressure of approximately 5 pounds per square foot at one end will still force the water to rise about 1 inch at the other end of the hose.  So it can be seen that the volume of water is not as significant as the applied force. 

Now let’s imagine that a fully enclosed, air tight box is attached to one end of the hose as shown at left.  Your objective is to put pressure on the open end of the hose and force the water to rise up into the enclosed box.  This time, however, physics tells us that there’s going to be little or no effect on the water level because the box at the other end of the hose is sealed shut.  This prevents displacement of the air in the box which prevents water from entering.  So even though there is an opening where the hose is connected, which is immediately adjacent to the water level, water entry into the box can be minimized or eliminated if the box is airtight.  This is the theory for installing an interior air seal to control water leakage around windows and doors. 

As noted previously, the installation instructions of many residential and commercial glazing system manufacturers now require that expansion foam or an elastomeric sealant with backer rod be provided on the interior around the perimeter of the window frame. In the section drawing at right, it can be seen that using a perimeter seal on both the interior and exterior of a typical storefront window results in an air space between the two seals.  Whether or not this air space is air tight depends on a number of factors including the integrity of the window frame as well as the substrate materials.  Nonetheless, while this space might not be absolutely air tight, the ability for air to enter into the sealed space can be significantly reduced.  As a result, if there were to be a failure of the exterior perimeter sealant the interior air seal minimizes air flow into the space around the perimeter of the frame.  And as we saw in our earlier experiment, if air can’t flow into this space, then water doesn’t flow into it either.  Several window manufacturers have conducted a battery of laboratory tests that confirm success of this installation.  And in addition to installation instructions, we’ve found that the Notice of Approval issued for many windows, doors, and glazing systems illustrate that an interior air seal is to be installed. 

When expanding foam is used as in the photo at left, only low expansion foams should be used in order to prevent excessive bowing of the window frame while the foam expands and cures.  Annex A.1 to ASTM E 2112-07 “Standard Practice for Installation of Exterior Windows, Doors and Skylights” is a very good guideline for using expansion foam around window frames.

In addition to being specified by many manufacturers’ installation instructions, the use of an interior air seal is also becoming noted in reference standards.  Paragraph 16.9.2 and 16.9.3 of AAMA IPCB-08, AAMA Standard Practice for the Installation of Windows and Doors in Commercial Buildings, require that after insulation is placed around the window, “backer rod should be placed over cavity insulation on the interior side of the window” and then, “place sealant over the backer rod in a continuous manner.”  Also, paragraph 3.5.3 of AAMA 502-08, Voluntary Specification for Field Testing of Newly Installed Fenestration Products requires that if field testing is conducted on windows and doors, “Care shall be taken not to disturb the interior side air seal, if present.” 

Unfortunately, many installers omit the interior air seal, which we suspect may simply result from a misunderstanding of its benefits.  We encourage installers and builders to take a second look at the potential advantages offered by installing an interior air seal in both new construction and renovation work.

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 wsmith@glazingconsultants.com 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.

Weathering the Wall and the Window

By William D. Smith

I was recently called in to analyze a mid-rise residential building undergoing repair because of water leakage problems. The photo on the right shows water damage to the wall sheathing at the sill of an opening after the windows were removed.

As often happens, the builder did not flash the sill of the openings. Instead, the window was installed first; then, a water resistive barrier (WRB) was installed, but it was improperly integrated into the window frame. As a result, water leaked into the wall damaging the sheathing and wall framing.

Fortunately, the problem was found soon after building occupancy, and as a result, the damage was not severe in this case. However, because the intensity of water leakage is often concealed from view, it’s not unusual to see very extensive structural damages.

Installation of windows and doors in wood or steel frame construction demands special attention to the waterproofing system on the wall. Although not part of a typical window assembly, and often not part of the window installer’s work, flashing of the rough openings and integration of the window frame into the WRB should not be overlooked or misunderstood.

Use of a WRB in frame construction is common, and it is a requirement of the building code. There are several manufacturers and variations of the WRB; many are provided in large rolls like sheet goods, while others are applied over the sheathing as a coating similar to paint. In either case, whether in residential or commercial construction and whether low-rise, mid-rise or high-rise, the WRB must be properly integrated into the window or door in order to provide continuity of the water barrier throughout the building envelope. Although not all WRB manufacturers also manufacture sill flashing materials, and therefore may not include sill flashing instructions, guidelines are available from many sources.

While some manufacturers provide adhesive backed tape, commonly known as “flashing tape,” that is intended to be applied over the edge of the window onto the surface of the WRB, flashing of the rough opening sill using a membrane or similar material that is lapped into the opening underneath the window is much more effective. This is not a new idea; I have carpentry manuals dating back 20 years and more that illustrate this basic concept using tarpaper. But unfortunately, the extra step of flashing the sill is sometimes not done simply because of time or costs constraints.

We encourage contractors to follow the WRB installation instructions and to be aware that, even if sill flashing instructions are not included, the use of sill flashing materials that lap into the rough opening underneath the window is highly preferred; the failure to do so could result in very costly repairs.

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 wsmith@glazingconsultants.com 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.