Retrofitting my house for tornado shelter?

In light of recent tornado posts I've been thinking about my house. Currently our storm room is the downstairs powder room but I'm wondering if we could somehow add a storm celler somehow. Being in Houston, we have no basement. Our house sits on a post-tension cable concrete slab. Is it possible to cut through such a slab and dig a shelter below it?

That would be really cool.

-Blast

Hey Blast, what about a storm shelter in the backyard? Probably cheaper to dig out, and install a pre-made shelter... ? Or even do one of the home made ones with the concrete rooms?

Seems it would be easier to build an underground shelter ten feet from the house, then add an enclosed hallway/anteroom that leads from the house to the shelter, with a reinforced doorway at both ends. Just build a shelter, sink it, reinforce it, then enclose entry. Like the fallout shelters from the 50's/60's, or "Saferoom".

> Our house sits on a post-tension cable concrete slab. Is it possible to cut
> through such a slab and dig a shelter below it?

No. We've got the same kind of slab, and our condo association documents provide this warning:
"Each residential structure in the Development has been constructed on a post-tension concrete slab. This slab is approximately 12 inches thick and contains stressed steel cables. Any drilling, excavating or other disturbance of the slab could damage the slab and cables and could result in serious injury. If damaged, the slab will not function as designed."

Where's the water table in Houston? How far down do you dig before you hit water?

I wanted something inside the house rather than having to run through the storm to the shelter. The water table is around 5' deep, maybe a little less here depending on recent rains, hence no basements.

Oh well, one more reason my next home will be a monolithic dome.
-Blast

Exactly!! Go to Italy, TX this October when they have their open house. You'll love it. I've done it twice. I also have drawn a few plans myself.

Standard Disclaimer

5' water table, wow you are lucky!

We need to talk. PM me tonight or tomorrow.

In the mean time, please do not cut your foundation. Hit a cable, and there is a good chance someone dies.

Imagine the pull string at the top of a dry cat food bag. Now imagine the cable is the string under 30,000 psi. Not a pretty site. Doesn't alway happen, but I have been there when it does.

You can trust me, I am you friendly Licensed Homebuilder in Texas.

Easy . . . Don't live in Texas. :-]

I know, I know, not helpful.

If you can't cut your slab, what about one of these right outside the back door? With the berm, it doesn't look deeper than 5'.

http://www.bargerandsons.com/storm-shelter/storm-shelter.html

We have a 10'x10' concret patio right outside the front door. I'm not sure if it's cable-tensioned or just poured concrete. I think it's just poured. I've been wanting it replaced with a nice pavestone patio someday. Maybe I could rip out the cement patio, put in a shelter, then have the pavestones placed over it...

My first choice is still the monolithic dome. Those things are amazing. Downside is finding an area around here that would 1) be rural enough to let me build it and 2) be urban enough for the DW. Her suggestion was a dome for me and a nice townhouse for her.

-Blast

Texas Tech's Wind Science and Engineering Research Center is probably a good place to look for information.

The usual problem guys run into with building a monolithic dome is the need to drive over to the wife's house to visit the family...

I don't see why an in-house shelter would cost $50k unless a lot of remodeling is done. The tricky part might be anchoring the shelter down in case a tornado throws a tree through the front door.

For the curious the website for David South's Monolithic Dome company is here.

I don't know anything about post-tension cable concrete slab construction, but this is a possibility if you can safely cut through the slab:

http://tswstormshelters.com/

Google "post-tension cable concrete construction" and you will find a ton of information.

Forget about cutting through a post-tensioned slab.

1) If you hit a cable someone could get seriously hurt.
2) When a cable gets cut your foundation is seriously compromised.
3) The only reason a post-tensioned foundation is installed is when the soil quality is bad.

As an architect I would suggest thinking of something else.

You might take a serious look at these...

http://www.familysafeshelters.com/existing.html


I have one and I have a friend that has one. Neither of us has tested them (Thank God) but they seem to be everything the manufacturer claims.

Standard disclaimers apply.

Hey, I like that! Do you have the 4x6 or 6x6?

-Blast

I got the "Beyond F5" model in a 4x8.

Blast,

There is a guy in Jerrell Texas doing the same thing. One of my previous homeowners did one after the fact. Not a bad idea at all.

Oh, I forgot to say. These things are like safes. Pick the size you think you need and then go up a size or two. I wish I had room for a bigger one.

Blast,

Don't give in to the dark side; build the Monolithic dome.

Standard Disclaimer

I'm just shocked, SHOCKED, that Blast said the word, "cut".

Cut?

tsk, tsk, tsk. Dear Sir, you need a nice Saturday afternoon, a six pack of PBR, five sticks of dynamite or modified shape charges, one bic lighter and large patch of backyard where you wish to put your new hole in the ground.

This method was strongly considered (though Shiner Bock rather than PBR). However, my property butts up against a 26" natural gas pipeline and the risk of excessive boominess is just too great.

-Blast

Do the pipeline owners/operators know you live there? They might offer you an incentive to relocate. lol

But oh what a nice boom it would be--even if it was your last.

Ah... Shiner Bock and explosives. It really doesn't get any better than that.

One of the best things about moving from MD to MO (apart from the gun laws) was that I can buy Shiner in the grocery store here. Woohoo!

I will say that living outside of TX has spoiled me as far as basements go, and I will never be without one again. And this built in concrete room thing totally rocks!

Greg

Blast,

The latest issue of Mother Earth News has an article on earth-bag building that would get you a relatively bomb or tornado proof outbuilding. You're a little tall to be a hobbit, but I guess you could change the decor a little.

http://www.motherearthnews.com/Do-It-Yourself/Earthbag-Building-Garden-Shed.aspx

Bill

Oh, that is cool! Not enough room left in my backyard, though. :-(
Hmmm, it triggers memories of a similar structure built out of bags of concrete. If I remember correctly a person stacked up unopened bags of cement, drove peices of rebar through it, then hosed everything down. The cement harden and the little house was ready.

-Blast

Blast, talk to Septic Tank Companies. They make Tornado Shelters that are very strong, above ground, and very effective.

Most folks have the shelters placed in the back yard and then (if they care enough to bother) have loads of dirt trucked in and placed on the sides and tops.

With that sort of slab going through it safely and effectively will be a major undertaking. It can be done but you would need to hire an engineer who specializes in such things ($), a contractor with experience is such things ($) who will use a lot of specialized equipment ($) to head off the cables and restore the integrity of the slab with a previously unplanned for hole in it. There is the construction motto: With enough time ($), materials ($), manpower ($), and money ($!$!$!)we can do anything.

Instead of all that how about a simple 6' or 8' square bump-out off the rear of the house. There are several small storm and tornado shelter designs that would fit in that footprint.

You would be building a free-standing storm room just a couple of inches off the back wall of your house. Ideally the design would be short enough to tuck underneath the roof overhang of the existing house as this would simply roof design. The gap between the existing house exterior and the shelter would be covered, inside and out, with a lightweight covering to keep the wind and rain out but designed to break away under if the house is swept away. Such shelters are required, for structural reasons, to be completely isolated from the house.

Typical shelter designs are typically 2x4s 16"OC with lots of connecting steel overlaid with double layers of 3/4" plywood and 18 ga galvanized steel sheet. Typical fastening of the exterior is 2" and 4" OC with 3" deck screws. Loads of screws. Those shelters are sometimes rated for an F-4 tornado (207 to 260 mph)and might give you some chance of surviving a F-5 (261 to 318 mph) as long as a windblown truck doesn't land on it. Once constructed the exterior of the shelter can be covered with material to match the exterior of the house.

Hmmm, that has some definite possibilities.
-Blast

Go round (he whispers enticingly) Go round. You know you want to.

Howdy everyone!
i kinda agree with that, i don't want running around to seek shelter over the storm room outside the home when my family could just go down and keep safe. Cut right through he slab. Try concrete safe room, built with concrete blocks and a poured concrete roof, is the way to go.  I didn’t feel like any wooden structure would be safe enough. The combination of stress changes and increased wind speeds can cause normal building components to fail. In new construction, one or more regular basement walls can be reinforced to use as shelter walls if they do not contain windows or other openings. The shelter must have a special ceiling that resists penetration from debris above.
nice insights regarding the matter, works well in clientele explanation for similar concerns and great concept for future endeavor of the project and information resource option. please do provide some photos of the frame for reference i would really appreciate it. have a great day ahead.



____________________________________________________________________
Evacuation is still the best way to avoid the full impact of these mega storms.
Matt Pierce
http://anteglobal.blog.ca
www.smartsafeshelters.com

Hi pie2mats! How about a quick introductory post?
-Blast

I say go the My name is earl way and dig a ditch to curl up in <.<

Found Vid =D

http://www.tbs.com/video/index.jsp?eref=google&oid=231496

Cut ta 1:20 In

do you have access to reasonably cheap sheet steel (1/4inch or so) from the Houston shipyards?....portable "shoot houses" are constructed of 4'x8' steel plate and connected at the corners with a sandwich of inner/outer angle iron

there are several seawall companies here on the west coast of Fla that make precast/prestressed seawall sections... they are tongue and groove, but you might find someone that would produce an easy to erect out bilding if you choose to not modify existing structure

the easiest, and probably most accessable for construction would to add two more block walls (with floor/ceiling vents) to an existing corner of your garage... hire a concrete pumper and try to vibrate as soupy a mix you can down the existing walls, rebar and solid pour new walls, add a steel inward opening door.. make a monolithic pour to the reinforced roof and lintel... add some bench seats...commode would be a nice touch

Speaking of "6' or 8' square bump-out off the rear of the house", go Monolithic. They're in your neighborhood -- okay, not really, but they are in Texas

it sure seems that a "wooden box" with the wall studs, ceiling and floor joist of 2x6 PT, on 12inch centers... sheathed interior and exterior (under floor included) with 5/8 or 3/4 plywood screwed to each stud...double layers of top plate and solid lintel over a steel door would be a viable option for a retro fit..you could skim it in sheet steel if so desired...if you could manage the height so you could get it under a garage door, and into a corner on a pallet jack you might have a cottage industry on your hand... and portable enough to move with you

a check with Texas A&M or Univ of Oklahoma, college of Civil Engineering should have the specs for such a construction

Belive it or not FEMA has free plans on building all type of shelters, ranging from basement concrete shelters to above ground wood or steel shelters.

http://www.fema.gov/plan/prevent/saferoom/fema320.shtm

Actually the entire FEMA320 document is a good reference.

It is quite possible to construct a tornado shelter out of a small, first floor, internal closet using mostly plywood. The idea is to create a thick wooden box that is securely connected to the foundation, that one can take refuge in during a tornado, yet still use as a closet the rest of the time. It is not real expensive.

It is not perfect, but it is a pretty fair shelter.

Under stairs is good too, nice angle on top to hopefully let anything falling slide down. Empty closet, rip out drywall. Drill and bolt the footers to the floor, screw the studs to the footers with strong deck screws. Cover with plywood, screw together with good construction screws, even use liquid nails for extra strength, re-cover with new drywall.

The strength of wood is that it is easily worked with common tools, it is inexpensive and holds together well when well designed. It is a project anyone handy could handle with little or no help. It isn't hard to design a structure that will stay together and erect with wood.

Its weakness is that it is hard to design in enough resistance to penetration to meet the forces involved with 2by4s coming end-on at high speed. A partial solution is to incorporate some sheet steel to boost resistance to penetration but the protection is not often complete and it both raises the price and difficulty of the construction process. Locating the room well inside a structure also helps as anything that would strike the room has to get through the rest of the house first.

Most commonly approved designs use a lot of poured concrete, usually in the form of concrete blocks with filled cells or expanded styrene forms, and rebar to hold it all together. The down side of this is that mixing and pouring concrete is labor intensive. Commercial mix trucks, or short-batch mixers, and pumping greatly reduces labor but pouring in an existing structure can be complicated and it is often more than a home handyman is comfortable doing even with help. Pumping and vibrating a yard or three of concrete is a job for at least three healthy people.

An experienced commercial concrete crew can set up and pour a small room in a couple of days so what they cost you might be offset with savings in time.

There is another form of concrete work, tilt-up panels, that can be worked by a couple of carpenters using concrete delivery trough-fed right off the truck. These wall and ceiling sections are laid out on flat ground or slab where the truck can get to them, formed up and the rebar and mesh is positioned like you would pouring a slab. After pouring and finishing the concrete is allowed to come up to strength and then the slabs are tilted up and shifted into position, and joined.

Blast this thread is almost 2 years old. Did you come to any conclusions on how this project will unfold or has it been completed?

I've been (comically) trying to convince my wife to convert our in ground swimming pool (3' to 9' deep dive pool) into a survival shelter and use the pool motor (converted to solar) as a power supply for a/c and and lighting. I could put all my prepper food, equipment in it and free up the house for her.

Wow I had no idea when I readeded this thread it was 2 years old. Really shows how a bump can breath life back into something....And how little I pay attention to details...

I am a HUGE Monolithic fan! That is the way to go Blast. I have toured their facility and designed a few homes and modified a few plans myself. Give it serious consideration.

Standard Disclaimer.

Another interesting option is to take advantage of companies producing a precast concrete items. This can be as simple and quick, but also as expensive, as buying a precast room or building.

These are used for rural equipment that has to resist heavy weather, vandals and the occasional hunter's bullet. Telcom and cell sites use these as do remote radar sites. Many manufacturers sell precast rooms that are rated to 150 mph winds and UL 752 Level 4 ballistic rating that covers a .30-06 Lead Core Soft Point bullet. Higher wind and ballistic rating are usually available as non-standard items with proportionally higher costs. This is a quick and easy way for those who are flush with cash.

Another alternative would be to buy a higher turnover precast item like a large septic tank and to adapt as either complete shelter structure or interior for an exterior concrete pour. An advantage to this is that standard tanks are usually delivered with a lift truck that will swing it into position for you. Once in position you finish interior and exterior or you rig spacers and a exterior pour form and then call in the concrete truck.

Another alternative using precast concrete is to buy standard precast concrete poles. Think of them as 8" x 8" x 8' reinforced concrete logs that you stack like you are building a log cabin. The US Army experimented with building bunkers out of these units and showed that you could stack and pin them together to build highly capable bunkers. Each log weighs about 600 pounds so a small crane and strong friends are going to help. The Army would horse them into position using a half dozen strong backs to haul each piece and build the bunker using nothing but hand tools, sweat, and harsh language.