On May 8, 11:44*am, wrote:
On Wed, 8 May 2013 05:48:53 -0700 (PDT), "





wrote:
On May 7, 8:20*pm, "Robert Green" wrote:
One other point. *You've doubtless seen the swath a big tornado cuts.. *Those
big twisters demolish wooden structures, roofs and all. *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. *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.

I'm sure you'd agree the speed of the wind is only one
factor. The winds you'd see in a hurricane are straightline
for the most part. With a tornado, they are strongly rotational.
Also,
with a tornado, you not only have high winds, but a very
localized low pressure, vacuuming effect that pulls
stuff apart. That force on a large roof area could be more
destructive than the wind speed. In fact, that is probably
what happens in many cases, isn't it? That the roof is
essentially sucked off, not blown off?


The connector requirements tie the roof, all the way down to the
foundation as a continuous system.

Yep. If the rest of the house isn't tied to the foundation,
then having the roof stay on could just mean the whole
house comes up and gets destroyed anyway.

I agree that it's a good idea to have the increased tie-downs.
Especially since with new construction, the added cost is
minimal. I just don't think in the case of a tornado, if the
house is directly in the path of an F3+, it's probably not
going to make a difference, in most cases. The farther
you are away from the center, then obviously the chances
of it making a difference that avoids total destruciton increases
a lot.