Severe Weather Events
Codes now require impact resistant windows and doors in the "wind-borne debris region" which includes the Gulf Coast, Florida, and the Atlantic Coast north to New England. Additionally, most schools are in increased risk category III because of the importance of protecting students and their higher occupancy loads.
Rigorous Testing
Impact-resistant windows and doors must pass rigorous standardized testing (ASTM E1886, E1996) to demonstrate protection against flying debris and storm intrusion. The superior structural performance and durability of aluminum extrusions, combined with laminated security glazing, offer impact-resistant products with greater performance.
Superior Strength
Elastic modulus (E) is a key measure of material stiffness and the ability to resist deformation under load. The typical elastic modulus for aluminum is 4-30 times greater than that for fiberglass, wood, or vinyl, allowing larger span, slimmer, and more elegant framing without sacrificing strength and rigidity. The average rated design pressure of aluminum framed windows listed with Miami-Dade county is 31% higher than wood and vinyl framed windows.
Furthermore, extreme weather events are increasing in all parts of the country - leading architects and engineers to consider higher wind loads in material and window selection in all regions.
Safety Shelter
Tragedies such as the 2011 tornado in Joplin, Missouri have raised awareness of storm protection for schools across the center of the country. Starting with the 2015 International Building Code (IBC), all schools with occupancy load greater than 50 and located in the 250 mph wind zone (indicated in red on the map) must have a storm shelter capable of housing all occupants.
The storm shelter may be part of the building, such as a gymnasium or auditorium, built to withstand very high wind loads and flying debris.
Windows and skylights in storm shelters – which are still desirable and necessary during normal everyday use for daylight, view, and ventilation – must meet very high impact resistance requirements under these high wind loads. Realistically, the very high structural impact requirements can only be met with metal framing and protective glazing.
Wind Load Resistance
Even where laminated glazing may not be required by the building code, aluminum framing will add structural performance and increase wind load resistance for added security in all locations. Architects should look for architectural grade "AW" rated windows and doors, the highest performance class under the North American Fenestration Standard (NAFS, AAMA/WDMA/CSA 101/I.S.2/A440). AW-rated windows must meet more stringent requirements for design pressure, maximum frame deflection, water penetration, air infiltration, durability, and life cycle testing. The added performance and durability of AW windows are particularly important in schools where safety, high use, and long lifetime are all critical factors.