Prepping for high wind
Since the resumption of this column for the 2013 hurricane season who have paid a lot of attention to protection of roofs from storm damage and their repair after the storm.
Starting today, however, we wish to look at two other features of our homes which the experts say are the most vulnerable after the roof, and which interesting, can place the rook at even greater risk if they are breached. We are talking about windows and doors.
Risks associated with windows and doors in hurricanes:
Windows and doors are important features of our homes that provide access, egress, light and view. They are installed in openings framed into our walls and consequently are frequently referred to as “openings” in building codes and engineering standards.
When a hurricane strikes, windows and doors can be blown open or broken, allowing wind and water to enter the home. Risks imposed by windows and doors rank right behind those associated with the failure of roof coverings.
Preventing the wall openings filled with windows and doors (including sliding glass doors and garage doors) from becoming openings through which wind and water can enter your home is an important part of protecting your home, your belongings, and your roof in a hurricane from the dual threats of wind pressures and wind-borne debris.
Vulnerability goes up significantly if you have a tile roof or if one or more of your neighbours has a tile roof or old shingles that are starting to curl.
The failure of windows and doors from wind pressure tends to be most frequent if they are older units that are not pressure rated, the units have been poorly installed in the openings, your home is exposed to the wind by being located near a large open area such as a field, a body of water or a golf course fairway or on the slope or top of a hill or escarpment.
When winds become high enough, damage to unprotected windows and doors becomes much more frequent. A study of homes impacted by Hurricane Charlie, conducted by the University of Florida, found that in areas where wind gusts exceeded 120 mph, about 33 per cent of the homes with unprotected windows had at least one broken window..
A study conducted by the United States National Association of Home Builders of damage to homes impacted by Hurricane Andrew, where gusts exceeded 155 mph, found more frequent damage to windows. They found that 64 per cent of the homes with unprotected windows had at least one broken window.
Window or door failures can increase risks of roof failures:
If your home is an older home you may not have hurricane clips or straps holding your roof structure to your walls. If that is the case, window and door protection may make the critical difference between losing your roof and keeping it on.
If a large window or door is broken open on the wall facing into the wind, the overall uplift forces that are trying to lift the roof off your house may be doubled. Research has shown that protecting the windows and doors can raise the wind speed required to lift your roof off your house by one to two hurricane intensity categories.
In other words, if it is likely that the roof of your home would lift off during a Category 2 hurricane if a large window broke open on the windward side of your house, it might take a Category 3 or possibly even a Category 4 storm to lift the roof off if all of the windows and doors are protected.
Installing shutters over windows and doors can protect them from the impacts of wind-borne debris and can keep wind pressures from building up in your house to the point where it significantly increases the uplift forces on the roof. However, it probably won’t keep the doors and windows from bursting open from wind pressure if they are weak or poorly anchored to the walls of the house.
Risks of water intrusion around windows and doors:
One building expert has suggested that there are only two types of windows and doors — those that leak and those that are going to leak. This comment actually contains a tremendous amount of truth since the test standards for water intrusion are set at a very small fraction of the design pressure for the window or door.
A realistic example is that if the window or door you have in your home is rated for 50 pounds per square foot of wind pressure (a pressure you might expect from a storm with wind gusts approaching 140 mph) it only has to resist a pressure of 7.5 pounds per square foot without leaking (a pressure that might occur when wind gusts reach about 55 mph) to pass the water intrusion test standard.
Since windows and doors are going to leak, the expert makes the point that the key is to minimise or manage the water intrusion. Keeping water from being driven against and building up on windows and doors is one way to try and minimise the water intrusion during a hurricane.