wrote in message
...
On Wed, 8 May 2013 05:48:53 -0700 (PDT), "
wrote:

On May 7, 8:20Â pm, "Robert Green" wrote:

One other point. Â You've doubtless seen the swath a big tornado cuts. Â
Those
big twisters demolish wooden structures, roofs and all. Â I still
contend
that no amount of bracing or improved roof attachment is going to matter
if
you're a stick-built house in the path of an F3 or greater. Â It's
sayonara
time for that structure as it gets pulverized and dragged into the next
county.

I agree. As I said previously, I can see addition roof connectors
helping
in the case where you're near the edge of the tornado path. But if
you're
directly in the path, it pretty much destroys the whole structure,
roof and
all. I suppose you could find some cases where it could have helped,
where there is a house or two, that for whatever reason was spared.
And if that house had the extra connectors, which is certainly a good
idea for any areas prone to extreme storms, then it could help that
house survive with it's roof intact. But in my view, that's the
exceptional
case.


Florida just bumped up the wind code requirement in this area to 170
MPH. That certainly starts getting you up into the F-3 tornado
category.
The connector requirements tie the roof, all the way down to the
foundation as a continuous system.

I did see what happens when a tornado overcomes this system. The
trusses actually broke where the clips held them and the top chords
went off in 3 pieces. The reinforced concrete block walls held.
One of the occupants was leaving through the open roof when her hubby
grabbed her ankles and they both came down and balled up until it
passed. Her hair was instant "buck wheat" style with hundreds of tiny
braids in it.



The best design I have ever seen that is tornado and tree-proof is a house
built into a poured concrete spindle
The technique is simple
1) Pour foundation
2) Pour vertical shaft to desired height
3) Build frame and pour into it what will be the roof
4) Raise roof to whatever is going to be floor height
5) Pour floor into frame
6) Raise roof & floor to next floor height
7) Repeat 5) & 6) until desired height is reached
8) Build casing around central shaft, fill with reinforced concrete to
support roof and floors.

The tallest I've seen is 3 stories with a widows walk / terrace on the roof.