Boca Raton Development Corp

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Hurricane-Resistant Glass Skylights Meet New Codes 

   Since Hurricane Andrew swept through Florida in 1992, there have been numerous changes in building codes in Southern Florida and other coastal areas. Much research and development of specialized hurricane-resistant products has taken place to meet new code requirements.
Many curtain wall, door and window manufacturers have invested considerable sums of money to develop new products or to enhance their existing lines, but few glass skylight manufacturers have ventured into the hurricane glazing arena.
At the time of this printing, only two glass skylight manufacturers have glass system approvals listed with Dade County. Check and see for yourself by logging on to Dade County's web site at
Glass skylight manufacturers are now realizing that the impact resistant code changes are here to stay. In fact, the Southern Building Code Congress (SBCCI) is placing significant weight on the need for impact-resistant glazing in most of their coastal jurisdictions. The insurance industry is also making it a financial necessity for building owners to participate on a voluntary basis even in coastal areas that still do not have mandatory impact codes in place. It is no longer a local or regional performance issue.
    Wind borne debris caused by hurricane force wind storms creates serious challenges on the structural integrity of the exterior cladding of a building. Once the exterior cladding is breached, internal pressures can double the uplift loading on a skylight, which could cause the glass to evacuate the framing system. Water and property damage is inevitable.
    To prevent the occurrence of such catastrophic damages, the South Florida and SBCCI code groups established missile impact design and test protocols for all exterior cladding systems of a building. They mandated a systems approach, not just for the glazing infill. The codes also devised large and small missile subdivisions in the test protocols to address the characteristics of wind borne debris.

Large Missile Requirements

    The large missile impact test standard for heights above grade up to 30 feet requires that a 2x4 wood stud (weighing 9 pounds) be fired from an air cannon at a speed of 50 fps. The test specimen is impacted at specific target locations: center of lite, 6 inches from one corner and at mid-span of the rafter framing member.
    The test specimen is then cycle loaded 4500 times under an increasing positive load and 4500 times under a decreasing negative load.
    The system must withstand the attack without allowing excessive venting or glazing withdrawal from the framing members. This test required that special laminated glass and unique methods of retaining the glass be employed.
    When considering large missile impact resistant glass for skylight applications, we must consider the need for high performance and ceramic frit coatings, as well as the integration of the same at the laminate surfaces. With the recent energy code mandates in effect, conventional tinted glass make-ups just don't work. Heat strengthening the plies of a laminated glass for large missile impact resistance and guarding against thermal stresses becomes an absolute must.

Small Missile Requirements

    The small missile hurricane-resistant requirements apply to installations over 30 feet above grade. Approximately 90 percent of the commercial skylight applications would fall under the small missile category.
    Test protocols for small missile tests vary from the large missile requirements. Three groupings of ten - 2 gram ball bearings are fired from an air cannon at a velocity of 130 fps at specific target locations. Typically, only the outer ply of the 9/16-inch heat-strengthened, laminated glass is broken by the ball bearing impacts.
    The impacted specimen is then load tested using the same cyclic procedures as for the large missile. Usually, the laminated glass infill exhibits little progressive damage or change after the cyclic testing is complete. Conventional skylight glazing techniques usually work with small missile applications.
    From a systems standpoint, the small missile testing can be more challenging due to the greater design and two times the test load requirements. It is very common at typical elevations and with coastal exposures to be faced with negative wind load conditions of 80-100 PSF or more.

Impact and Mock Testing

    The codes require that a minimum of three specimens be impacted and cycle tested to provide the empirical data for product control approval. The testing must be performed by a code approved laboratory.
    Requirements include that a full-scale mock-up of the representative system (incorporating the same glass size(s) as used for the impact specimens) be tested on slope for air, water and structural resistance at the lowest pitch or slope intended for use. Dade County requires that the mock-up be tested for static water resistance at a minimum of 15 percent of the positive design load. The structural overload test pressures are twice the design load, which is more severe than the one and a half ASTM E330 overload criteria.
    Hurricane-resistant skylight design becomes much more challenging when we consider the high wind loads and the double over load criteria. Heavy shear blocks, reinforced splice and moment connections, closer fastener spacing and custom silicone glazing details must be documented as the base line for further rational analysis.

Code Approval

    Some of the code jurisdictions require that the skylight system be approved before the installation for the specific building project can begin. This places even more emphasis on the importance of pre-planning during the submittal process. The procedures and processing time for securing a code approval, which involve much more than a typical AAMA/ASTM mock-up test, will prove to be a time consuming and costly experience.
    The reliability of the skylight manufacturer to execute the code approval as required by the contract documents becomes critical to the ultimate completion of the project. Contractors and owners need to evaluate the track record of a skylight manufacturer's expertise and ability to complete hurricane-resistant projects on schedule.
    Pre-planning with code compliance offices and partnering with reliable suppliers and a reputable test laboratory are critical in the development of a successful hurricane resistant skylight. Often, the code protocols do not cover all design aspects of custom glass skylights. Resolving the unknowns in the design development stage can save considerable time and money.
    With storms like Hurricane Andrew and Hurricane George making headlines, manufacturers will have to continue improving products to meet coastal requirements. Hurricane-resistant glazing systems will be a critical element in minimizing property damage and the loss of human lives during future storms.

Upcoming Design, Testing and Code Changes

    The American Society of Civil Engineers (ASCE) have updated their building design standards (ASCE 7-98) to include revised wind speed maps and wind borne debris criteria (Article for areas with wind speeds exceeding 110 mph (within one mile of coast) and 120 mph for all other areas.
    Florida is currently working on developing a new state code which should be adopted next year.
    SBCCI, with it's SSTD 12-97" protocol for windborne debris, changed the original roof gravel standard to steel ball bearings for the small missile test. Recently, Palm Beach 
County, Florida mandated SBCCI product approval for hurricane-resistant applications and after 6-30-99 will no longer accept Dade County test reports.
    The new ASTM E1886-97 missile impact test standard and the ASTM E1996 impact 
specifications (based upon a national consensus) will create standardization in the 
hurricane-resistant industry.
    With the creation of the new International Building Code (IBC), we should see the 
influences of the ASCE, ASTM and SBCCI on hurricane design and testing by year end, 2000.
    Joe Schultheis is Custom Products Manager for Naturalite Skylight Systems, part of The 
Vistawall Group. Naturalite has been involved in hurricane design, testing and product 
development since 1996.

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