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Potential Openings in the Building Envelope
for Wind and RainThree items should be considered when installing a door or window: the door or window, the frame and the hardware. All three are important to maintain the door or window system strength. Failure of any one item can result in a breach of the building envelope and cause damage to the home. The door or window, frame and hardware should be able to withstand both wind load and impact from wind-borne debris.
Protecting windows, entry doors, sliding glass doors, gable end vents and skylights is the most affordable and effective way to secure the building envelope and ensure building integrity during high wind events. Many products and systems are available to meet this challenge, however, it is critical that any product or system be both tested and approved for wind load and wind-borne debris. The Building Code Compliance Office of Miami-Dade County maintains the most complete listing of approved protective systems. The list is available at (305) 375-2901, or find it online at: www.buildingcodeonline.com.
Windows
Unprotected standard glass windows and doors can be penetrated easily by wind-borne debris in hurricane winds, thus allowing entry of damaging water and wind. Once the window glass fails, the subsequent pressurization of the structure can cause total destruction of the house. Even if the house withstands the wind pressure, the interior may still be lost due to water damage. Therefore, all glass —whether it is annealed, tempered, reinforced or insulated — needs to be protected during a hurricane. The only exception is impact-resistant window glass, which has been shown to maintain a secure building envelope during a high wind event.
There are two main approaches to retrofitting windows to improve their resistance to wind-borne debris impacts and wind pressure changes: impact-resistant (laminated) glass systems and shutter systems.
Impact-Resistant Glass Systems
Passive Protective Systems
Shutter Systems
Shutters are the most common devices for protecting windows and doors and come in a variety of styles and materials. Choices include permanent or temporary shutter systems for use on windows, skylights, gable end vents, sliding glass doors, exterior doors and garage doors.
Permanent Shutters
Permanent shutters should be installed by trained individuals and according to the manufacturer’s specifications to ensure proper protection. Factors to consider when choosing a shutter system are approval status, design and test results for wind and impact resistance.
Permanent shutter styles include Bahamas, roll downs,
accordion and Colonial.
Permanent shutter types and styles in “Bahamas,” roll-downs, accordion, awning and “Colonial.” Choosing a shutter style can be based on several criteria, including the building location in relation to the coast and the cost and ease of operation. Ease of operation is an important factor to consider because if shutters are too hard to close, owners may not use them. If shutters cover windows on an upper floor or hard-to-reach location, they should be operable from the inside. Roll down shutters are often the easiest to operate in these conditions.
Temporary Shutters
Temporary shutter systems are designed to withstand wind-borne debris impacts and wind loads during a hurricane. They are commercially available in many types of materials including steel, aluminum and clear, see-through plastic.
Temporary shutters are typically corrugated panels that come in standard widths and can be joined to cover wider openings. The mounting hardware for temporary shutter systems should be installed well before hurricane season by trained individuals and according to the manufacturer’s specifications. Each panel should be clearly labeled to aid in quick installation, and should also bear approval labels.
Tips for Wind and Wild Fire Resistance: Using glass products that can withstand high wind, potential convection and radiant heat can offer double protection value. Selected glass may offer additional protection from heat exposure that might otherwise cause glass to fracture and collapse. This scenario would leave an opening for flames to enter and ignite the interior of a structure. Tempered glass will withstand much higher temperatures than plate glass and should be used for large windows— particularly windows overlooking slopes or vegetation. Double pane glass is slightly more resistant to heat than single pane glass.
Entry Doors and Sliding Glass Doors
Entry door systems designed and certified to resist hurricane force winds and wind-borne debris impacts are currently available to consumers and contractors. Purchasing and installing a hurricane-resistant certified door is an option if doors are being considered for replacement. When retrofitting doors, there are three specific items that need to be secured:
- The door
- The frame
- The installation hardware
Exterior Doors
Exterior doors must either be strong enough to resist wind-borne debris impact loads and wind pressures, or be protected with an approved shutter system. Only solid wood or metal doors should be used to replace existing doors. Hollow wood doors can fail under wind and impact loads in a hurricane.
The doorframe must be securely mounted to the wall system. Additional fasteners should be added to strengthen frames as needed. Improperly attached frames could fail in a hurricane and allow wind and water to damage the house. Evaluating an existing door to determine quality and integrity of the frame’s original installation might be difficult. If possible, pry up a length of door molding to determine the amount and type of fasteners used. If there is concern or doubt about the frame’s structural integrity, add screws around the frame that are long enough to penetrate to the framing members.
Hardware quality is another factor to consider when retrofitting for added strength and durability in existing doors. Every door should be secured with three hinges and a 1-inch minimum dead bolt throw. Hinge screws should extend into the framing members, not just into the doorframe. Double-entry doors should also have surface or integral bolts installed on the passive door that are secured to the top framing member and to the floor.
Sliding Glass Doors
Sliding glass doors should be impact-resistant or protected by a tested and approved system. The sliding doors should be mounted securely in their frames, so they cannot be pushed in or pulled out under hurricane wind loads. The frame should be securely attached to the wall so that it does not fail under load. During retrofitting, it is important to ensure proper frame installation by checking all mounting holes and the condition of the original fasteners. If any mounting holes are not used, or if any of the fasteners have deteriorated, new fasteners should be installed.
Garage Doors
Garage door failure allows winds to enter the house causing catastrophic failure.
Garage doors are the most vulnerable to hurricane force winds for two reasons: the relatively long span of opening that they cover, and the weak materials from which they are usually built. Many garage doors are constructed from lightweight materials to conserve weight and expense. Although their lighter weight makes them easier to raise and lower, it also makes them less resistant to the wind and impact forces of a hurricane.
Garage door assemblies have three potential weak areas:
Two options are available to address the weaknesses in garage doors:
Replace the Garage Door
Blueprint for Safety recommends replacing the existing garage door and track with a system designed to withstand wind load and wind-borne debris. Garage doors that are tested and certified as passing the South Florida Building Code requirements for large missile impact test, SBCCI’s SSTD 12 test standard, or the ASTM E1996 test standard have been found to provide appropriate levels of hurricane protection.
Protecting the Garage Door Opening
A second option for protecting the garage door is to construct and install a protective shutter system that completely covers the garage door opening. Garage door shutter construction is identical to the construction and installation for a window. However, the extra span needs to be considered and supported as if it were a large window.
Gable End Vents
Gable end vents require protection to prevent wind-driven rain from entering the house.
A complete retrofit plan includes covering gable end vents. These vents are often overlooked and need protection from wind-driven rain and debris impact. Retrofitting gable end vents with storm shutters will diminish the threat of damage. Otherwise the vents could allow significant wind-driven rainwater into the house, ruining insulation, drywall, carpeting and personal possessions.
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