Storm Shelter under slab Foundation?

jessiegrayJanuary 30, 2012

I've never owned a house with a storm shelter, basement, crawl space etc. But am in the process of researching for our next build and read somewhere that storm shelters/basements are usually not built under houses with slab this correct?

We've always built mostly on slabs in my area (Lower Alabama). For our next house we are still planning to use a slab foundation but would like access to a storm shelter/small basement (20'x 10' ish). We have no need for a huge basement that extends the entire size of the main floor, just a room large enough to ride out hurricanes/tornadoes which frequent the area. We're not building in a "flood zone" so flooding isn't usually an issue, just high winds, tornadoes and the occasional pine tree falling on your house.

Any advice or information on building a small concrete room underneath a slab foundation?

Link to the house plan we're using (basement access is near front entry door):

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Pretty hard to get out if the house collapses on the slab.

While objects can end up over the entrance, at least not having tons of possible debris over it to start might be a good idea.

    Bookmark   January 30, 2012 at 3:56PM
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Sophie Wheeler

You don't build a basement under a slab. You build a basement for a portion of the build and build that part of the home on the basement walls and floor joists as the foundation. The rest of the build is built with slab foundation.

In most of the South, basements aren't the best idea due to high water tables. They are extremely problematic to waterproof correctly as well, leading to pretty high costs from builders who seldom do construction this way. Your money would go further to have a separate capsule storm shelter. I've seen them for as little as $1500. They're just large concrete capsules that get some soil thrown onto them. A septic tank with an entrance.

I've been through 4 tornadoes in my time on earth, and I wouldn't bother with a storm shelter. A well constructed home done to high wind standards will withstand any inland blow from a hurricane, and if you use the cable turnbuckle system for hold down in addition to the proper Simpson ties at every juncture, a home will even withstand a tornado trying to rip it off of it's foundation. Build it with ICF, and you've just eliminated 90% of the chance for any penetration danger. It will all cost about the same as trying to put in a basement with a high water table..

    Bookmark   January 30, 2012 at 5:30PM
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Epiarch Designs

good suggestion above, and ICF has many other advantages that may make it worth your consideration.

However you do not need to go underground at all. There are products out there that allows for slab on grade construction but using a storm room. DuPont Stormroom is something we have used on a project before. It is a room kit that is assembled and bolted together and to the slab. It comes in a variety of sizes and for our project we used it as a file storage room for a city hall. Most home owners use it as a walk in closet or something in their home so it actually has a purpose.

    Bookmark   January 30, 2012 at 5:47PM
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In most of the South, basements aren't the best idea due to high water tables. They are extremely problematic to waterproof correctly as well, leading to pretty high costs from builders who seldom do construction this way.

What part of the south are you in? This may be true of some areas, but not where we live. Almost everyone I know has a finished basement with no water problems. Of course there are exceptions, but those few live where underground water/springs are common after heavy rainfall.

DD2 lives in slab home, and after the tornadoes we've had in Alabama, DH heard about a shelter that bolts to the garage floor. There are others that go under the garage during construction. You can also have an existing closet made into a tornado safe room. A friend of mine in Louisiana had her MBR closet built as a safe room during construction.

Here is a link that might be useful: one safe room

    Bookmark   January 30, 2012 at 10:11PM
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Here is another:

Here is a link that might be useful: steel safe rooms

    Bookmark   January 30, 2012 at 10:12PM
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ICF is the way to go. Forget spending money on a storm shelter. Spend it on making the whole house better.

    Bookmark   January 30, 2012 at 10:17PM
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Thanks everyone for all the advice.
We really like the ICF idea but couple concerns, wouldn't a smaller concrete "safe room" be safer/stronger than the ICF since once the roof comes off (which it will if it's wood) you'll be surrounded by flying debris? We also wanted the room to double as a panic room ( we've been robbed before while at home) and a safe for valuables, once the burglars get past the front door and ICF exterior they'll basically be in your panic room. So we'd still have to build a concrete room inside our ICF house to accommodate those needs. Can anyone think of another solution to?

Was thinking that with the basement 2/3 could be storm shelter and the back 1/3 would be a panic room/safe. We live 2 hrs from the coast and our whole town is much higher above sea level than surrounding cities, we know a few with basements and no water issues unless they're outside access and rain water is able to get through the doors. There is actually a house down the road that was built completely underground, so water isn't too big of an issue except maybe during April-may (rainy season).

    Bookmark   January 31, 2012 at 10:51AM
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Your home safety concerns seem a bit excessive, so you might want to assess your building locale further before you get too far into planning. Perhaps a gated community would be more suited to your needs.

You can easily pour interior ICF walls at the same time that your exterior is being poured if you require a safe room. You can even pour a concrete cap to it if you wish. Do further research on the new building methods of seismic/high wind construction. They will keep a hip roof on your house in a full blown hurricane quite well.

    Bookmark   January 31, 2012 at 1:28PM
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One of the main features I requested in the house we're building is a safe area to wait out a storm/tornado/etc. Yes, it's probably excessive but I pushed for it. Note, we have no history of tornadoes hitting the area. LOL. Estimated extra cost is probably ~$10k.

Our safe room is in the basement. It has poured concrete walls/floor/ceiling. I highly suggest that if you build one to add some type of secondary concealed emergency exit. I would not want to get stuck and die inside a safe room. That would be ironic. lol.

Our safe room is about 6ft x 20ft interior dimension.

    Bookmark   February 1, 2012 at 12:35PM
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Think I'd go with an underground out on the property like in the "good ol' days". It can be used as a wine cellar, root cellar, and canning storage for veggies and fruits. It could also be a reading room, radio communications room, or other hobby type room as well. Kind of a getaway place and hopefully never have to be used as a safe room!

    Bookmark   February 1, 2012 at 1:12PM
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I recall visiting my Great Aunt when I was small. The small little house was built on a bit of hill. No storm cellar. They bought an old schoolbus at a surplus auction, and after stripping the motor, gas tank, etc, they parked it next to the little hill. Then my Great Uncle used the backhoe to bury everything but the doors. It just made it look like the hill was slightly bigger and flatter on top than it really was and gave them space for a bit more back yard. Instant tornado shelter! It was the absolute coolest clubhouse for kids too. Well, as long as you didn't mind the spiders that is.

No, not recommending that you do that. :) Just saying that if you go ICF, a basement is pretty easy to accomplish, and there's no point in not having a full basement space under the house. It's cheap storage space, or shop space or teen hangout space.

    Bookmark   February 1, 2012 at 2:34PM
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tncraft - What did you use as a secondary exit? Tunnel, stairs leading outside of house? That was our first concern was getting stuck if the house fell on the basement door, some forums mention breathable air can become a concern in the concrete rooms too so second exit is a good idea.

Yeah this idea does seem excessive to some, but better safe than sorry right? When SHTF everyone will be crowded around my basement trying to break in to my vienna sausage and tuna reserves ;)j/k but unless you've went through Hurricane Katrina or cleaned up the damage from the Tornado that hit Tuscaloosa, AL last year then you just can't understand what it's like. I have two children and if a 10k basement only saves them once in their lifetime it'll be worth every penny and being labeled as crazy ;)

live_wire_oak - My grandfather did the same thing but used a large round cylinder (maybe was used to hold oil?), he only had to use it once during Hurricane Fredrick, it saved 10 peoples lives (my mother included) a tornado hit during the hurricane and went straight through the house. The cylinder was pounded a few yards away but stayed in the ground. I think some beams penetrated it but not enough to reach everyone inside. I say use whatever works.

    Bookmark   February 2, 2012 at 11:49AM
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jessiegray... One side of our safe room is a little exposed or we're going to grade it to where part of it will be exposed and not totally below ground. That's where our concealed emergency exit is going to be.

    Bookmark   February 4, 2012 at 10:27AM
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couple of thoughts here...

we are in the process of moving forward with building and will have a storm shelter incorporated in our home.

we currently have an in-ground one outside that is sufficient, yet is not very practical. you either watch the weather and are like "well its coming so lets go sit out there for two hours waiting on it" - or you watch the radar and before it hits you go out there. the downside to both is - well the first is obivous and the second is that you may be running through pouring down rain/ hail to get in the shelter. once in - since its made of concrete - cell phone reception is the pits. i can only imagine what it would be like in a shelter built within a slab.

the growing trend that we have seen are the interior storm rooms - pick you choice of materials. or if nothing else - you could put one in your garage/storage room where you wouldnt have to go outside.

    Bookmark   February 6, 2012 at 9:38AM
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I'm thinking that GreenDesigns must have stock in ICF because he/she sure loves it and thinks that it will survive WWIII. lol....

    Bookmark   February 7, 2012 at 9:19PM
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I hope this is appropriate for this thread. With all the tornadoes the past few years it seems prudent to have some shelter.

I came across the following shelter that can be retrofitted into an existing slab:

my concerns are:

1) would installation lead to foundation instability ?
2) does it need ventilation
3) if debris falls on the door do you think it would still open? (it slides)

    Bookmark   March 3, 2012 at 9:14PM
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Timely thread. Tornado hit Harrisburg, Il very close to my hometown and near where my family still lives. Scary stuff. I read today that you should go to NE corner of basement not south like previously thought.

Ot I know, but interesting.

I wouldn't have a house without a basement unless I had no choice.

    Bookmark   March 4, 2012 at 6:35PM
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