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RE: Tornado Alley construction[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Tornado Alley construction
- From: "Jerry Coombs" <JCoombs(--nospam--at)carollo.com>
- Date: Mon, 09 Jun 2008 05:52:49 -0700
I live here in TX. No req'd residential code, except that FINALLY in '04 they adopted the IRC as a "default" code. That means that if a municipality has a residential code in place, they don't have to use it. Doesn't matter if the code they're using has much lower standards. Many "Building Officials" (usually not required to be certified) modify the code at their whims. Also, I said municipalities. Doesn't apply to unincorporated county areas. Most houses are built by prescriptive codes, whether or not they meet prescriptive criteria. Oh, and residential contr'rs don't have to be licensed.
My house got hit by an F1 tornado last Spring. Straight-line winds were measured at about 90 mph just before it went circular. One would expect a fair amount of cosmetic damage. It was built in '03. Almost totaled the house. Ripped about a fourth of the roof deck off. They use staples here, and about half of those miss joists. No one checks that stuff. Staples on shingles, too, They go fast. Staples on siding, no rafter clips. The rain that follows does lots of damage. pulled about half the brick away. Missing ties, and they use those useless corrigated ties anyway.
What wasn't taken into account was that the second story floor joists rolled about 5 degrees, domino style. Missing or unfitted blocking, and missing or improper rim (band) joist. Sill plates are nailed down. The house tilted laterally because no one checks shear walls.
Point: Damage gets greatly exascerbated when houses are not built to a real code. BTW, insurance here is about $008 on the dollar, based on sale price.
>>> On 6/6/2008 at 4:06 PM, "Scott Maxwell" <smaxwell(--nospam--at)umich.edu> wrote:
That article kind of glances over the fact that it was an F1 tornado (a baby tornado on the Fujita Scale)...talking wind speeds that are 73 to 112 mph. Now, I am not saying that I would want to be sitting there gawking at it as it headed for me, but in the grand scheme of things it ain't bad at all. Add to that the fact that according to the article it never got closer than 3/4 of mile to "well built houses". Thus, while the straps and anchor bolts (assuming installed properly and such) are a very good thing and I am certainly not suggesting that they are a bad I did, I would argue in the case outlined in the article it is a rather decent stretch to believe that they were the reason why there was no damage...the more likely reason was at the location of those homes, the winds speeds likely did not even get past the standard wind design speed for most of the country (90 mph) as dictated by code.
What the article neglects to mention is that _IF_ you are in the path of a serious tornado (say F3 or higher), there is likely not much one can do to prevent your home from being majorly trashed without doing MAJOR overdesign (i.e. forget wood...we are talking CMU or R/C with a significant amount of reinforcing...and even then there are situations where projectiles in very substantial tornados can still penetrate unreinforced CMU or concrete sections...take a look at the description of an F5 on this page: http://www.tornadoproject.com/fscale/fscale.htm ...note the part that says: "steel reinforced concrete structures badly damaged.") relative to current codes. The current codes in the US don't come any where near designing homes to with stand direct hits of a tornado...and it is not just because tornado alley jurisdictions may not require straps or such. The reality is that if an F3 or greater directly hits your home, all the straps in the world will likely not save it...they might mitigate the damage...it is debateable if they will mitigate the damage enough that the home would be savagable...but then strictly speaking, traditionally codes are not about the financial health or repairability of the structure but rather does the structure survive long enough and well enough so that your tushie is largely unharmed in any significant way.
I will say it again...I am not saying that straps and such are NOT a good idea...they are. But, they should not give someone the false sense of security that if an F3 or greater tornado (maybe even a F2) that directly hits their house that their house will be unscathed or even minimally damaged...if you have a direct hit of an F3 or greater, your house is most likely toast, with or without straps.
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