For simplicity shutters, windows, and doors that have been proven to resist the impact from large windborne debris (defined by the test standards as a 9-pound 2x4 lumber missile striking end on at 34 mph) are referred to as impact rated products. Just because you live in an area where the building code requires windborne debris protection and you buy a new shutter, window, or door does NOT mean it is impact rated. It has to be a product that has passed the testing required by the debris impact test standard and it must be properly installed. Each product that is approved for installation on homes in the State of Florida will have a Product Approval that includes installation requirements. If your shutters, windows, or doors are impact rated products with a Florida product approval appropriate for your area (more about that in the next paragraph) and they have been installed according to the manufacturer’s installation requirements, then you know that they comply with the minimum requirements of the building code for your area. You are not relying on word of mouth or a salesman’s pitch.
If you live in Miami-Dade or Broward counties (High Velocity Hurricane Zone, (HVHZ)) your new shutters, windows, or doors have to meet (have a product approval indicating it meets) the 1st standard listed below. If you live elsewhere in Florida your new shutters, windows, or doors have to meet the 1st or 2nd standards listed below. This is what the building department will check when you or your contractor applies for a building permit prior to installation and what a building inspector will verify was installed. The building inspector will also inspect to ensure that the product was installed in compliance with the requirements of the product approval (the manufacturer’s installation requirements) when he inspects after installation. Specifics of installation requirements may well vary according to the wind zone and exposure category that are dependent on the geographical location of your house.
Shutter and Awning systems have been in use for over 200 years. They can be designed to provide protection from wind and water, increase security, block solar heat from the sun, increase privacy, and some are designed for purely decorative use. Here we focus on their impact resistance and the test standards that have been developed in the last 20 years to assess their ability to provide protection from windborne debris. Shutter systems may also provide some additional protection from water damage. However, this is not their primary purpose nor are they tested in any way to determine a specific level of water penetration protection. Impact resistant shutter systems are designed to protect the openings in a house from the type of failure that will lead to a huge increase in internal pressure in the house and reduce the likelihood of hurricane propelled flying debris from entering through the openings.
All houses leak air around windows and doors, and a myriad of other gaps and cracks. Since the roof and three of the four walls typically see negative or outward acting pressures as the wind blows at and around a house, normal leakage results in the internal pressure being slightly negative, which would tend to help hold the roof down and the side and back walls from being pulled outward. If an opening is created on the windward side of the house that is large enough to allow enough wind flow into the house to overcome the leaks through all of the other walls and roof (attic), then the pressure that would have occurred at that opening builds up in the house, much like someone blowing up a balloon. That pressure buildup works to try and push the roof up and the side and back walls outward, in the same direction as the forces caused by the wind blowing around the house. In some cases, this internal pressure can double the uplift on the roof or the outward forces on the side and rear walls. Research has shown that the internal pressure begins to build up when the opening on the windward face reaches about 1% of the area of the wall and the internal pressure completely follows the pressure that would have occurred at the opening when the area of the opening reaches about 4% of the area of the wall. By protecting the openings from the kind of failure that can lead to internal pressurization and the reduction in the chances of debris entering your house, shutters significantly decrease the chances that the house will be pulled and pushed apart by the wind and they provide increased safety for occupants sheltered inside. This is the primary function of an impact resistant shutter system. The impact resistant testing standards are designed to establish the shutter’s ability to meet the minimum level of protection as defined in building codes for Windborne Debris Areas of the country.
Test Standards: National model building codes, such as the International Residential Code, define the Windborne Debris Areas as areas in hurricane prone regions where the design wind speed is greater than or equal to 120 mph and areas within 1 mile of the coast in hurricane prone regions where the design wind speed is greater than or equal to 110 mph. These design wind speeds and the resulting map for Florida (see Priorities and Incentives) are defined as 3-second gust wind speeds occurring at a height of 33 feet (10 meters) above the ground at an open location like an airport.
Impact rated residential doors and windows or the protective systems for doors and windows are tested to determine their ability to resist the impact of large wind borne debris (missiles) by shooting 2x4s of specified lengths and weights against them at specific speeds. Several different groups have developed engineering standards that establish missile sizes, test methods and acceptance criteria for the tests. For houses, the typical large missile test consists of a 9-pound 2x4 piece of lumber impacting the shutter or product end on at 34 mph.
The referenced standards for opening protection in hurricane windborne debris area are listed below with numbers so that they can be referred to more briefly later.
By now it is probably clear that the performance requirements for Miami-Dade are higher than for the rest of Florida. For some products there is no cost premium for meeting the higher performance requirements of Miami-Dade or Broward Counties. If there is a difference in price you may want to weigh the advantages vs. cost of meeting the higher performance standard.
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Certified Home Inspector.