Section 1: Protection for Windows and Vents

Window Protection

source: FL Division of Emergency Management

According to the Florida Division of Emergency Management, homeowners should consider three things when they need to increase hurricane protection of a home through window protection. They include:

Breaking glass prevention

Bolstering window frame anchorages

Reducing or eliminating the potential for water intrusion

The above can be accomplished in several ways. The most common are described below. They are:

     •  Retrofitting old windows with approved impact resistant windows
     •  Improving existing window anchoring systems with approved methods
     •  Reducing leaks through approved sealing methods
     •  Installing approved and effective shuttering systems


Impact Resistant Retrofits

• When a window fails from the impact of a projectile, it allows the buildup of high internal pressures on the structure. Subsequently, the structure is likely to fail in some fashion.
• When wind driven rain is propelled against windows which are not designed for this environmental extreme, water intrusion into the structure is likely to occur. Additionally, if a projectile fractures a non-impact resistant window, water intrusion is guaranteed to occur.
  

What determines an impact resistant window or door?

Tests which measure impact resistance are normally performed by shooting 2x4s at various speeds. The following are normally accepted tests by groups that have developed standards for impact resistance. When testing impact resistance for homes, a piece of 2x4 lumber weighing 9 pounds is fired at the window or door at 34 mph (50 feet per second). The following are normally accepted standards for these tests:

Florida Building Code:
• TAS 201 Large and Small Missile Test Standards
• TAS 202 Uniform Structural Load Standards
• TAS 203 Uniform Cyclic Pressure Test Standards

ASTM (American Society Testing Materials)
• ASTM E 1886 Standard Test Method for Performance of Exterior Windows, Curtain Walls,   Doors, and Storm Shutters Impacted by Missile(s)
• ASTM E 1996 Standard Specification for Performance of Exterior Windows, Curtain Walls,   Doors and Storm Shutters Impacted by Windborne Debris in Hurricanes.

Southern Building Code Congress International
• SBCCI Test Standard for Determining Impact Resistance From Windborne Debris   SSTD-  12-99

When using an impact resistant product for a retrofit, it should have passed one or more of these standard tests and have a certificate indicating such.

Improving Anchorages

Securing Existing Windows

Homes built prior to the creation of storm resistant building codes often have windows which are inadequately secured to the structure’s frame. When these structures are subjected to high winds, the window fails by being pushed in. The Florida Division of Emergency Management provides the following facts:

• A 50 mph wind pushes a window with 5 to 7 pounds of force per square foot.
• A 100 mph wind pushes a window with 20 to 28 pounds of force per square foot.
• A 130 mph wind pushes a window with 30 to 34 pounds of force per square foot.
• A 3 foot x 5 foot window in a 100 mph wind will have 300 to 420 pounds of force against the window (and the frame of the window).

Most windows, especially older windows, are not designed to withstand this amount of force. Many existing anchorages for older windows in older homes can be improved. The following recommendations are from the Florida Division of Emergency Management .

Strengthening Windows in Frame Walls

• Use screws long enough to penetrate the window jamb through the sheathing well into a framing member
• Be aware of the space that sometimes exists between the window and wall where the window has been shimmed.
• When driving the screw, do not over tighten where the window frame begins to warp.
• Wood screws should be a minimum #10 size.
• Spacing should be at the bottom and top on each side with additional fasteners at 12” on center.

• Tapcons are the normally recommended fastener for this application
• Fastener must be long enough to penetrate the window jamb, the shim space, any wood strips, and into the masonry a minimum of 1 ½”.
• Be aware of possible interference of screw head with operation of window.
• Pre-drilling is usually necessary as per fastener manufacturer’s instructions.
• When driving the screw, do not over tighten where the window frame begins to warp.
• Tapcons can be 3/16" diameter minimum.
• Spacing should be at the bottom and top on each side with additional fasteners at 12” on center.

Reducing Water Intrusion

Leaks at Windows

The Florida Division of Emergency Management also has recommendations for sealing existing window openings. Sealing window frames actually accomplishes two very important tasks.

1. Improves the strength of the window frame against high winds.
2. Provides a barrier to potential water intrusion.

• When the gap between the frame of the window and the sash is only as large as the thickness of a couple of sheets of paper it can cumulatively result in a much larger area than one might think.
• As an example, if an egress window sash of 36" wide by about 36" high, the perimeter crack 72" long. The area of the crack accumulates to be equivalent in area to a square hole with 1 inch sides. In a hurricane this could be like someone standing outside with a garden hose squirting it through your window. Imagine how much water can come through.

Window manufacturers are working on designs that are less likely to leak, but most of the high performance windows currently available are for commercial buildings and cost considerably more, are rarely operable, and look a lot different than windows for homes.

Some homeowners have applied tape between a window sash and the frame from the inside. This will be completely ineffective at keeping water out during a hurricane event. If tape is used, it will be more effective on the outside (if it is water resistant. Duct tape has been recently shown to actually help protect against water intrusion when used in this fashion. It should be noted, however, that this is an unproven and untested method.

The Florida Division of Emergency Management suggests the application of caulk to the outside of the window frame as an effective sealant. Note the Department’s following recommendations:

• Use a good quality caulk such as a urethane caulk.
• A good bead of caulk around a window that is wetted to the surface of the house and the window can provide a lot of strength and secondarily provide a barrier to water entry.
• Regular silicone caulks are not recommended.
• If you use white caulk select one formulated to be UV resistant so it does not turn yellow.
• The bead of caulk should not be left so the shape is concave because this does not leave the caulk thick enough to be very effective. Further it is likely to crack because of temperature changes.
• Running a finger along the joint does substantially reduce the effectiveness of the caulk, but it can be beneficial to assure adhesion of caulk by pressing it into the two surfaces to form a concave shape. If this is done, add a continuous bead of caulk to this first layer so that there is enough thickness for the caulk to react to temperature changes without cracking.

Shuttering Systems

According to the Florida Division of Emergency Management, the least expensive way to protect existing windows and damage in hurricanes is to install tested and approved impact-resistant shutters over all windows. They protect windows from common wind-borne objects and also can reduce damage caused by pressurization of structure if a window. In protecting structure openings from storm damage, shutters remain the most common device homeowners use. The shutters can be classified into two major categories; “permanent shutters” and “temporary shutters”. Shutters, whether permanent or temporary, are typically used to cover all openings on a structure where failure in a storm may occur. These may include windows, glass doors, gable vents, skylights, exterior doors and garage doors.

Storm shutters

In a FEMA (Federal Emergency Management Agency) publication entitled “Against the Wind”, a team of experts examined homes that had failed and ones that had survived during Hurricane Andrew in Florida. Three of the four areas of weakness that should be checked included openings in the structure. Specifically, windows, doors, and if you have one, a garage door were mentioned.

The report went on to indicate that installing storm shutters over all exposed windows and other glass surfaces is one of the easiest and most effective methods of protection. It was recommended that all windows, French style doors, sliding glass doors, and skylights be covered with some sort of shuttering system to protect the openings during a storm.

The FEMA report on "Shutter Alternatives" goes on to ask the question:

Why Are Storm Shutters Needed?

The report explains that shutters remain an important part of a hurricane-resistant home because they provide protection for glass doors and windows against windborne debris. Another important reason that shutters should be used is that they keep the building envelope intact (i.e., no window or door breakage). During a major windstorm this is vital to the structural integrity of the building. When the envelope is breached there is a sudden pressurization of the interior which can cause major structural damage (e.g., roof loss). The structural damage, if even to a minor degree will then lead to a third potential damage factor: water intrusion. Water intrusion, caused by water driven rain, will cause significant interior and contents damage. It has been found to be the most costly of all three of these types of damage from storms.

Permanent Style Shutters

In the category of permanent style shutters, there are many manufactured types available. When using manufactured types, the installer must follow the manufacturer’s instructions. Prior to installation of permanent style shutters, it is recommended that the installer check with local building officials to find out if a building permit is required. Additionally, be sure that the Florida Building Code is being followed.