For our large (~50'x50') "storm-proof" building, which rises about 8 feet above grade, we are thinking of either 8" or 10" of concrete in the walls. We're thinking we might need to go up to 10"; I am afraid of scenarios like if a 300+mph tornado throws a car into the building. But I'm also wondering, whether we can obtain a similar projectile resistance by using heavy gauge (between 10 and 20 ga) metal siding on our building. Doing 10" along with heavy siding is probably out of the budget. If we did 10" instead, we would probably do cheap vinyl, or maybe 24/26 gauge metal depending on the budget.

What do you think?

Is it impossible to obtain a truly "storm-proof" (record-breaking tornados) building that isn't underground (without it getting exponentially more expensive)? I've read conflicting opinions about this online.

I am new to this, so forgive me if this concrete/siding comparison is ridiculous.

Thanks

Okay, if you're using solid concrete walls, tornado rating for them is usually 6-8".
So if you're going with 8" concrete walls, you should be fine.
Just talk with your architect about your rebar schedule, possibly look into Helix micro-rebar, and talk them and your concrete supplier about appropriate concrete mixes.
Also are you going with a concrete roof as well? You can get by with trusses with hurricane strapping, but a concrete roof would be the most bulletproof option.


If you have a tornado land RIGHT ON TOP OF YOU, you're screwed. PERIOD. It'll basically destroy anything right underneath unless you're buried into the earth and have insane amounts of ground tie-in (think large deep, branching concrete piers underneath and a massive concrete plate, with similar piers over the top).

But, for 99% of everything else, a concrete building with sufficient ground-tie-in, of sufficient mass should be perfectly fine.

If you're worried about a car being thrown into a building, read this page and watch the videos:

http://www.quadlock.com/insulating-concrete-forms/icf_house_car_crash.htm

The pertinent part starts here:

https://youtu.be/0B81NZUqT2Q?t=227

You'll see the Hardie-bard siding and the foam layers were stripped off. But the 6" concrete wall underneath was basically untouched (a couple chips).

As for steel plate siding. Siding can be stripped off by wind shear.


Basically, engineer your foundation or foundation/slab right. Tie the walls in properly. Tie the roof in properly. And you're pretty much good to go.

This is not to say the house WON'T be damaged. You can still have windows and such blown out and your home exposed to the elements.

And yeah, if the tornado lobs something big enough, the building structure may need repairs afterward.
But it shouldn't come down around your ears.

This video:

https://youtu.be/Qid176aGtkg?t=300

Is about a project in hawaii for stormproofing. The timecode I included takes you to a window covering system for storms. Essentially it's a double-sided bolt with the outer bolt being removable.
In clear weather, the fixture is covered by caps to keep the fixtures clean.
In inclement weather, you pop the caps off, screw in the outer studs, fit your plywood over the openings, then you have hand-tightened lugs you screw down to hold them in place.

Just some things to think about.

Thank you for all that useful information.
I guess we won't bother with heavy siding since it does seem likely that it could detach quickly in the event of a storm if it is just drilled into the plastic studs.

What you said about any above ground building whatsoever being destroyed in the event of a direct hit by a particularly strong tornado seems plausible, but I'm not sure if I am convinced. Is it really much more severe a threat than a car that is thrown into the building? We might be able to go below grade a few feet but not underground entirely. Luckily there are no windows, though.

A big enough, strong enough tornado will pretty much scour anything off the surface, given appropriate amounts of time.

Just make sure everything is anchored to everything else properly and you should be fine for 99.99% of everything.

As to more severe threat than a car thrown through a building? HELL YES.

Remember, cars these days are DESIGNED to deform and crush safely upon impact.
The chances of a tornado chucking an old solid steel Studebaker at you are slim...

Think "steel i-beam", or "tractor" or "lamp post".
Hell, think "remnants of your neighbor's home".

Also, if you go with something other than a concrete roof, think about capping a single "safe room" in the building with a concrete ceiling.

I see, thank you. We are planning on going with a concrete roof I think- probably Litedeck. I'm not sure how much concrete we would want to put on it but probably on the thicker side. Edit:I shouldsay 'maybe' Litedeck because I really haven't done much research on that yet.