Tornado shelters

[Tigers!]

With the recent spate of tornadoes across Mississippi it had me wondering about tornado shelters.

1. Are they compulsory for home owners or public is such areas?
2. Would such a shelter work? Or like a bomb shelter only work provided it was not a direct hit?
3. Could a tornado shelter be built cost effectively for houses?

 

[Elixir]

With the recent spate of tornadoes across Mississippi it had me wondering about tornado shelters.

1. Are they compulsory for home owners or public is such areas?
2. Would such a shelter work? Or like a bomb shelter only work provided it was not a direct hit?
3. Could a tornado shelter be built cost effectively for houses?

Basements work pretty well, even in a direct hit. The big deal with tornados is debris flying sideways. Underground that isn’t a problem.

 

[Bronzeage]

Tornado shelters certainly work. The great majority of deaths and injuries from a tornado are from flying debris. Any degree of shelter is better than being in the open air. Shelters are a difficult cost-benefit calculation. I've live in the south all of my life and never seen a tornado.
Energy efficiency requirements and building codes have to shoulder some of the blame. As houses became better sealed, a sudden drop in barometric pressure can basically cause a house to inflate and rupture. This was especially seen in mobile homes, which can inflate and burst like a balloon. This is why they have the nickname "tornado magnets". A mobile home doesn't have to be in the path of a tornado to be damaged, just close enough for the drop in air pressure.

There is no practical way to reduce property damage from a tornado. The best investment in protecting lives is in prediction, identification, and advanced warning.

If a house doesn't have a basement, some people build a concrete vault as part of their house. It can be used as storage space in regular times. Tornadoes are brief, so emergency supplies are usually flashlights, batteries, and water.

Side note: Before Hurricane Katrina, the previous 30 years had seen 24 deaths from hurricanes. Most of those were people who were blown off their roof while trying to nail down a tarp.

 

[robnisch]

Just texted a friend in northern Alabama. Nearest one was 17 miles from his place.

 

[steve_bank]

Search om Florida hurricane building codes. There are probably videos on it.

Search on tornado shelters.

 

[Ruth Harris]

I am not aware of any place that requires storm shelters by law.

Shelters do work. In the old days, most families took shelter in their "cellar". For those who don't know, this was a small underground room where home canned goods and root vegetables were stored after harvest to keep them edible through the winter. For those who lived in cities, it was not uncommon for them to dig out a similar room in their yard; my dad did this in Kansas City. These small rooms could be beside/under the house or freestanding in the yard, had an exterior entrance, and they saved many lives over the years. I don't know if they could survive a direct hit as I have never heard of one having that happen.

I suspect a modern shelter would be fairly expensive, given the requirements in place for habitable spaces.

Ruth

 

[Tigers!]

I was curious about whether they are deemed necessary for houses etc. to have one in certain areas.

 

[Elixir]

I was curious about whether they are deemed necessary for houses etc. to have one in certain areas.

Don’t know but I’m sure that if they mandate a location for a shelter, it’s not in the attic!

 

[steve_bank]

Looked online, you can buy them for around 4-10k$

Form the recnt level of damage a shelter in a house may not be enough. A semi truck was lifted into the air. A concrete block buried in the ground would be a good solution.

If I lived in tornado country that is what I would do. If I built a house it would be a poured concrete reinforced dome.

 

[Loren Pechtel]

With the recent spate of tornadoes across Mississippi it had me wondering about tornado shelters.

1. Are they compulsory for home owners or public is such areas?
2. Would such a shelter work? Or like a bomb shelter only work provided it was not a direct hit?
3. Could a tornado shelter be built cost effectively for houses?

I've never heard of them being compulsory anywhere but that doesn't prove nobody mandates them.

They do work, normally you're not actually trying to build something that can stand up to a direct hit, but rather something that can avoid taking that direct hit in the first place. Putting it underground avoids any chance of a direct hit, you only need to stand up to debris. This is why they recommend going to the basement if a tornado threatens--even with nothing more your chances are pretty good. Go into the basement and build something that can stand up to the weight of the house above if it collapses and you should expect to walk away from even a direct hit by a F5.

If you don't have a basement you can accomplish pretty much the same thing by building a room underground and putting a door on top designed to stand up to a tornado--not that hard a requirement in that scenario.

Now, if you want to give the finger to that F5 while not underground it takes a fair amount of engineering. Normal home construction techniques will not suffice, but concrete domes inherently come pretty close--simply building the dome strong enough to act as a dome gives it the strength to laugh at the F5 itself but you'll need to beef it up a bit to stand up to the worst the F5 can throw at it. (And I mean "throw at it" quite literally--flying debris.)

 

[Loren Pechtel]

I am not aware of any place that requires storm shelters by law.

Shelters do work. In the old days, most families took shelter in their "cellar". For those who don't know, this was a small underground room where home canned goods and root vegetables were stored after harvest to keep them edible through the winter. For those who lived in cities, it was not uncommon for them to dig out a similar room in their yard; my dad did this in Kansas City. These small rooms could be beside/under the house or freestanding in the yard, had an exterior entrance, and they saved many lives over the years. I don't know if they could survive a direct hit as I have never heard of one having that happen.

I suspect a modern shelter would be fairly expensive, given the requirements in place for habitable spaces.

Ruth

But they don't really need to be a habitable space--nobody's going to live there, just hide while the tornado roars.

 

[Loren Pechtel]

If I lived in tornado country that is what I would do. If I built a house it would be a poured concrete reinforced dome.

???

Poured concrete dome?! How do you do that? I've looked at concrete domes and I find the idea quite attractive but what I've seen is gunite, not poured.

(And, yes, a dome would cause all sorts of insanity of curved walls--the solution is you don't. Build a more conventional house (except it's all interior-type construction) inside the dome. The wacky spaces between the house and dome don't matter. The huge thermal mass of the dome goes a long way towards reducing your heating/cooling costs, especially if you put your insulation outside it (ideal: polyurethane, topped with a thin layer of concrete. Polyurethane insulation is normally considered a fire danger but if it's outside the dome it's not a threat.)

 

[Ruth Harris]

But they don't really need to be a habitable space--nobody's going to live there, just hide while the tornado roars.

In places that have building codes (most cities, some counties, some states) any enclosed space which is intended for human occupancy, no matter the reason or length of time, have structural requirements. In those places you can no longer just dig out an underground space and call it good without being subject to some pretty hefty fines. I had a friend who found this out the hard way; the local building codes required specific engineering specs and inspections during construction to verify that the building codes were followed - even for a storm shelter.

Ruth

 

[steve_bank]

Concrete reinforced domes are not uusual.

Concrete is pumped from a truck through a hose.

Up the street is an apartment building under construction. Concrete is pumped up 7 or 8 stories form the ground.

For a dome build the forms, put in the rebar, and pump in the concrete. Pour in stages.

Or build in sections.

[URL fixed]

https://www.monolithic.org/domes

onolithic Domes meet FEMA standards for providing near-absolute protection and have a proven ability to survive tornadoes, hurricanes, earthquakes, most manmade disasters, fire, termites and rot.

They are cost-efficient, earth-friendly, extremely durable and easily maintained. Most importantly, a Monolithic Dome uses about 50% less energy for heating and cooling than a same-size, conventionally constructed building.

Beginning in 1970, Monolithic Domes have been built and are in use in virtually every American state and in Canada, Mexico, South America, Europe, Asia, Africa and Australia.

 

[Loren Pechtel]

Concrete reinforced domes are not uusual.

Concrete is pumped from a truck through a hose.

Up the street is an apartment building under construction. Concrete is pumped up 7 or 8 stories form the ground.

For a dome build the forms, put in the rebar, and pump in the concrete. Pour in stages.

Or build in sections.

https://www.monolithic.org/do

onolithic Domes meet FEMA standards for providing near-absolute protection and have a proven ability to survive tornadoes, hurricanes, earthquakes, most manmade disasters, fire, termites and rot.

They are cost-efficient, earth-friendly, extremely durable and easily maintained. Most importantly, a Monolithic Dome uses about 50% less energy for heating and cooling than a same-size, conventionally constructed building.

Beginning in 1970, Monolithic Domes have been built and are in use in virtually every American state and in Canada, Mexico, South America, Europe, Asia, Africa and Australia.

Yeah, those Monolithic domes are impressive. But note they're gunite, not poured.

 

[barbos]

Would such a shelter work? Or like a bomb shelter only work provided it was not a direct hit?

The one I used would certainly work. Direct or indirect hit, does not matter.
It was an reinforced concrete half-pipe vault, probably 15cm thick.

 

[Loren Pechtel]

Yeah, those Monolithic domes are impressive. But note they're gunite, not poured.

Update: I see I'm slightly wrong--shotcrete, not gunite. Same basic concept, slight difference in technique.