Posted By toddm on 02 Jun 2013 10:05 PM
The reality is that the walls, roof, windows, doors and garage doors must be missile-resistant and the connections of the structural elements must be capable of withstanding 250 mph wind pressures. Missile resistance of walls and even roofs is fairly easy to achieve with current ICF (insulating concrete form) construction, however the connections for long span roofs and tall walls to transfer the loads induced by a 250 mph wind must be 7 ½ times stronger than those routinely required by today’s codes

Not that it's directly pertinent to a home in tornado areas but consider this. I worked at a DOE Strategic Petroleum Reserve oil storage site south of Baton Rouge, LA. We built a new shelter building over the pump pad. The AE firm stated that the most economical and sensible approach to deal with Category 4 and above hurricane winds was to fasten the sheet metal siding so that in winds above 120 mph the siding would peel off and blow away. The naked steel skeleton frame would then withstand all projected winds above 120 mph. If the siding were fastened so securely that it would not come off, the resultant wind forces would be enough to collapse the entire building.

So, in order to preserve the most costly part of the building it was cheaper to sacrifice the lower cost part of it. Of course, in this case time is normally available to move people out of the way so people protection was not a critical factor like the issue is with tornadoes.

It's kind of like the back door my brother had on his veterinary clinic. Burglars were bound to break in to look for drugs and money, so he put a cheap door there and left $20 in the open till. The money and the cheap door was much cheaper to replace than was a secure "burglar proof" door and the damage done to the building was a lot less. Sometimes it makes more sense to proactively control an allowable loss rather than try to prevent any loss.

I remember Hurricane Andrew in south FL. My nephew was a news photographer who was sent to ride out the storm and record the damage. One of the most shocking images I saw was a large chunk of concrete with re-bar sticking out of it that landed on I-95. It was thought to be part of a building on Homestead AFB. Officially, Andrew was only 160 MPH (before the weather instruments blew away), but there were embedded tornadoes. After seeing that, I would always go under ground in a tornado, regardless of the house construction.

I'm building ICF for a variety of reasons. Here in upstate SC, tornadoes are generally small, and not all that common. With a direct hit, I know my stick-built roof will be gone or damaged, but I'll be in the basement, in my safe room. Although I up-graded the trusses, and used more anchor bolts and better hurricane clips, I harbor no illusions as to what a direct hit would do. If I lived in EF-5 country, I would have an underground shelter if i didn't have a basement.

Posted By toddm on 02 Jun 2013 10:05 PM

Wow the ICf shills are in full cry....

Then to be fair, you are an AAC shill because anytime the topic comes up, you talk it up and disagree with top experts and even call out Martin Holladay from Green Building Advisor and claim that his statements are "BS". When the ICF guy claims his power bill is $50, you attack him, yet you do the same thing when you talk about AAC.

Posted By toddm on 14 Apr 2013 12:50 PM

The GBA posts are nonsense in my opinion.

Posted By toddm on 24 Apr 2013 09:18 AM

I established earlier that Martin Holladay's "horrendous bridging" is also BS. Ditto for his diss of effective R value being marketing hype. I turned the mini split off in mid March, even with morning lows this week at 32-45 degrees. (My overhangs have reduced the sun to a 3 foot strip on great room floor.) My power bill for March was $37. I you want, I'll post a picture of it.

AAC is a terrible choice if your thing, like Lbear's, is that the sky is falling. In the act of crushing, AAC would slow missiles enough to de-deadly them -- the first one anyway -- but the structure would look like swiss cheese. It should be standing still if the vertical concrete cores are tied properly to the slab; alas that would be a pyrrhic victory. On the plus side, AAC would be easier to 'doze into a pile than unsalvageable icf.

I reemphasize here that I am not Chicken Little. After 20 twister free years in Texas, I know from experience that a miss by 300 feet is as good as a miss by 300 miles. That said, my choice in tornado country would be a cast-in-place Tmass-like SCIP with at least four inches of concrete on the exterior and conventional stucco parged over that. A good stucco crew should have the thing patched in a day or two, although you'd have to paint it in perpetuity. If you kept a collection of Monets in your library, you could cast a concrete second floor tied to the scip walls, in a two-story structure with a small, albeit disposable, conventional roof. You would then have a choice: upstairs vulnerable; downstairs secure.

I like TMass walls but I have to remind myself that Tmass is not a true composite wall.  Only one wythe of concrete gets counted in the structural calculations.  At least, that is what I am told by structural engineers.  I understand the EASI-WALL System is a true composite wall.

What Alton says. The important parts are having a concrete exterior that can take a hit, a cast second floor that completes the concrete box, and a .small roof. And a price tag that won't make you feel foolish when the storm never comes.

I like TMass walls but I have to remind myself that Tmass is not a true composite wall. 

Looks like that have various systems with the NC system only being structural on one side. Evidently to prevent "thermal bowing".