A reader writes about new construction:
Tornado-proof-ness is my concern. I like wood. But concrete seems sturdier. I am building a home.
It’s an interesting point – just how likely is any given home in the United States, or in tornado prone areas, to be hit by a tornado? I did a little poking around the web and ran across this page from 2005 by Chuck Doswell, who, according to Wikipedia, is
… an American meteorologist and prolific severe convective storms researcher. Doswell is a seminal contributor, along with Leslie R. Lemon, to the modern conception of the supercell, which was developed originally by Keith Browning.[3] He also has done research on forecasting and forecast verification, especially for severe convective storms, and is an advocate of ingredients-based forecasting.
So, with those credentials, Doswell leads us through a calculation of probabilities given a number of very rough assumptions. His conclusion?
If I assume that the figure of 1 chance in 10 million annually is crudely representative of the odds of experiencing F4-F5 winds, then what about over the lifetime of a family’s residency in the home? I’m going to assume that lifetime is about 30 years. [some pointless nattering about binomial distributions removed – Hue] … In 30 years of living in that house, there are roughly 3 chances in 1,000,000 of having that home flattened by the F4-F5 winds in a violent tornado. This is important, because for frame homes that are secured to their foundations, the chances of riding out (i.e. without serious injury or death) a tornado up to F3 intensity in an interior room of the home are pretty good … interior walls should still be standing. It is only in F4 and F5 tornadoes that avoiding becoming a casualty during a direct hit by a violent tornado when aboveground in an interior room (provided the home is reasonably well-constructed and secured to the foundation) becomes doubtful. Having a special shelter built into a new home to withstand violent tornado hits aboveground costs about $1000-$3000. Retrofitting such a shelter into an existing home would be more expensive. Assuming it’s possible to build a below-ground tornado shelter near the home, it probably would be cost roughly $1000-$3000, as well. Given the low odds of experiencing a violent tornado, it is not obvious how to make the decision to have or not to have a tornado shelter built. The decision has to be a personal one. Peace of mind might be worth something to you, even though the odds of actually experiencing the violent winds in a violent tornado are pretty tiny.
There might be local “tornado alleys” or other factors where the chances might increase by as much as another 2-3 orders of magnitude, although there is no objective evidence for this at the moment. If over the 30-year lifetime of your house, you had about 3 chances in 10,000 of having your home wiped off the foundation by a violent tornado, would you buy a shelter then? What about with 3 chances in 1000?
I’ll not pretend this is anything like a full analysis, for which I’d want to consider subjects such as structure survivability comparisons of the two materials, climate change gas emission comparisons, and how well home replacement insurance stacks up against climate change gas emissions. But it’s an interesting start, as is the paper.
