WINDOWS/OPENINGS: IMPACT RESISTANCE
Any unprotected openings should be designed to resist large and small missile impact below 30 feet in height and small missile impact above 30 feet in height. The specific large missile size and velocity are determined by building code, and windows are tested per test standards ASTM E1886 and ASTM E1996. In general, impact resistance requires laminated glass, which is structurally glazed to the frame, so the glass remains intact following an impact.
If windows are not impact-rated, replacement with impact-rated windows should be considered. If an impact-rated glass is used, the wind-pressure resistance of the glass, frame and attachments to the primary structure are then reviewed to confirm the window will carry structural loads back to the building structure. The water-penetration resistance of windows should also be considered because they will be subject to heavy wind-driven rains during a design event.
Hurricane shutters also may be used to provide hurricane-impact protection. If hurricane shutters are used, the windows will be protected from the design wind pressures and from wind-driven rain, but the shutters and the attachment of the shutters must be reviewed for wind-pressure resistance.
For large glass openings, such as curtainwall and window wall, post- installed lamination films and edge sealants may be considered as a retrofit option to provide impact resistance.
LOUVERS
Like windows, exterior louvers also are subject to large and small missile impact requirements. In addition, louvers often can be a source for water infiltration during hurricanes if not properly specified. Specialized louvers for high- wind-velocity regions that are tested and rated in accordance with AMCA 550 “Test Method for High Velocity Wind Driven Rain Resistant Louvers” should
be used.
ROOF-EDGE CONDITIONS
Structural failures under high-wind events are often initiated by failures of roof-edge details. Roof-edge failures can lead to a progressive failure because wind is able to penetrate under the roof membrane and unzip the entire roof. Current building codes require roof-edge metal and coping to comply with the test methods of ANSI/SPRI ES-1 to prevent roof-edge failures. Roof-edge metal attachments should be reviewed in evaluating existing enclosures for retrofit.
EXTERIOR WALL ASSEMBLIES/ CLADDING ATTACHMENTS
During a hurricane event, exterior walls are subject to high positive and high negative wind pressures and may also see debris impact. The underlying wall structure should be evaluated to determine if a structural retrofit is necessary. Like roofing, the capacity of the base wall structure determines the feasibility of retrofitting the exterior cladding and attachments. Wall cladding failures typically occur because of negative wind pressures (suction) and failures often occur at building corners where suction pressures are higher. During evaluation, attention should be focused on these regions. Often, the same cladding attachment methods are used for the field of walls as the corners, which can result in failures at the building corners where wind pressures are higher.
REVOLVING DOORS
Revolving doors are also a part of the evaluation process for hurricane resistance. Revolving doors are intentionally designed to fold flat and “pancake” under high pressures as a safety feature for building egress. This can result in the failure of revolving doors under high wind pressures. Revolving doors should be protected during high wind events or consider replacing them with vestibule features.
The Time Is Now
There are many factors to consider when evaluating existing building enclosures for a hurricane-hardening retrofit. The key steps to put in place during this review process are:
- Establish the desired post-event performance.
- Establish the design event criteria (wind speeds and wind pressures).
- Evaluate the existing building structure and feasibility of the structural retrofit if needed.
- Evaluate the existing building enclosure elements and retrofit up to the capacity of the underlying structure.
We all want to be prepared in the event of a hurricane. As the old saying goes “a chain is only as strong as its weakest link”. Taking a holistic proactive approach in evaluating the primary structure in concert with the building enclosure is key to a successful retrofit. Hurricane season is upon us. Let’s be ready!