In California, Tennessee, Alaska and many other states we require that a structure be designed for earthquake loads. Is that pessimistic? Last time Tennessee had a major quake was almost 200 years ago, however we have written the codes with the understanding that loss of life would be extremely high the New Madrid goes off, unless we design with the anticipation of a major quake. It is estimated that the last New Madrid quake topped 8.0. At that level the soil liquefies, farm fields look like the gulf on a rough day and tall buildings look like wet spaghetti.
With such things in mind we design for anticipated problems happening rather than hoping that they do not. Building codes attempt to balance the odds of something happening with the cost to implement a protective measure. The goal is protecting the lives of the occupants. If we designed for sunny warm days then a nice tent would serve most everyone well. The reality is that it gets cold so we need insulation, it gets windy so we need a certain strengths to resist the winds. Much of Florida has design winds of 130 to 150 mph. For the average house that works out to roughly 27 to 55 lbs per square foot for the entire side of the house, windows included. With that in mind remember that your living room floor is only rated at 40 lbs per square foot. One important purpose of the impact rated window is to maintain the integrity of the structural envelope. Once the windows go field research of hurricane damaged structures shows that the house will likely loose its roof, exposing the contents to wind and rain.
We also need to include in the cost analysis the cost of putting all those nails in the hurricane ties. The bill for the metal may be a couple of thousand, but the cost to put 8 to 32 nails per strap is much much higher. Many manufactures and engineers require that all the nail holes in the ties be filled with a nail in order to get any strength from the tie. Major labor cost.
My point is that in order for a structure to resist hurricane forces the house must work as a complete structural system. All of the components have to work together. The house is only as strong as its weakest component. Nature loves to exploit weaknesses.
BTW nature does not recognize building codes. There is no law of nature that says that the winds cannot top 140 mph along the emerald coast or that the gusts must be limited to 3 seconds. That was just what the code committee agreed on base on the best information that they had available. It was not that long ago that the code committee thought that the trees would protect the houses in this area and thus the design wind forces could be reduced.
