underground shelter

[lynches lumber]

Ok guys, now that the introduction have been made and the welcomes had been extended, lets put our thinking caps on and get down to business. I didn't come here for my health. Need some expert advice. The boss lady has been after me for years to build an underground shelter. She was in a mobile home in a tornado years ago and is terrified of bad storms. So now that I have the means of sawing my own lumber thought I might earn some brownie points. I've read oljarheads root cellar plans and they sound good but want the shelter a little more like home since sometimes it may have to double as the doghouse.
  Ok. Heres what I got in mind. 2x10 pt floor system sitting on 12x12 concrete blocks with a small crawl space. The reason for the crawl space is to give any water a place to go. it will be graded to a slope and a sump pump for removal. On top of the floor system will be a moisture barrier with 3/4 plywood on top of it. 2x6 @12" centers for walls. 2x10 slightly sloped rafters/joist. The rafters will have a center beam(not sure what size yet). The floor system will also have a center beam to transfer the load. Also probably a center post under the beam for more support. The entire sheathing will be diagonal 1x's. Entire thing wrapped in 60 mil moisture membrane. Oh about to forget. The thing will be 12x12 and about 2 ft. under ground. Ok thats about it. Critique as needed. Don't want the thing to fall on my head.

[lynches lumber]

Aint it funny how you think of things to put into a post after youve posted it. The 2x10 rafters will be on 12" centers also. Also there may be chance a tractor could drive over it  occasionally.

[mmhailey]

If you really want a tornado shelter, aka a " Storm House", then I would use your rough cut wood for forming, and build masonry walls, and pour a 4" slab over the top. The sump pump is a good idea, but a drain, with a sump backup might be better.

The engineering for the roof, to support x amount of weight is well beyond me, but maybe someone else could chime in. Obviously 12' free span is too large without supports.

Good luck.

[lynches lumber]

yes a 12' span would be to much that's why there will be a beam under the center, so actually its only a 6 ' span. I'm still concerned about the weight load of the 2' top fill and the possibility of going over it with the tractor. Concrete is out of the question except for what I can mix in the mixer such as the footings for the block piers.

[beenthere]

Will this be connected to your existing home? And does the existing home have a basement, a crawl space, or on a slab?

[lynches lumber]

The house is on a slab. The entrance to the shelter will be from a porch. There is good slope from the house so the porch is off the ground on the end. Want to get close to the house but dont want to disturb the ground right up next to it. Got enough cracks in the concrete as it is.

[Ironwood]

There is ALOT of info on the web about sheltering. Look up "survival forums" , one that comes to mind is "when the s%^t hits the fan" WTSHTF.  Also "Equipped to Survive" folks have compiled alot of resources there about what you are  contemplating. I like the Equipped to Survive, fairly level headed and well run.

Ironwood

[Rooster]

Spancrete for the roof...no interior posts!

http://www.spancrete-sma.com/faq.php?location=10

[ljmathias]

Just remember that water and moisture will not be your friends for this.  Rubber coating the outside walls and doing everything you can to drains run off away will help but you may still find damp walls and dingy atmosphere inside- mold, fungus and critters love such places... I know.

Lj

[beenthere]

Lj
Those were my thoughts too, and why I asked about the house. Being it is on a slab, that makes it more difficult to go beneath the house (where the timber ceiling would stay dry and the "shelter" would be less damp, etc. ).

But trying out some various ideas of design before digging and building will be a good plan.

[Jim_Rogers]

My first thoughts about this "idea" was "how are you going to quickly access this storm cellar?"

In order to be able to quickly run out of your house and down into the storm cellar you going to need some stairs. Some easy stairs so that you aren't trying to climb down a ladder or something like that.
You need quick and easy access for the women who will be using this in an emergency.

I drew up a cross section to see what it may look like if it was built with some easy stairs to see how big an area would be needed to make them easy to run down into the storm cellar.

This is what I got:



As you can see by the dimension string on the right, I have set off some lines based on what lynches lumber said he wanted.
That is two feet of soil, then 1" of sheathing, then 2x10 rafter, then a support beam (assumed an 8x8 for strength) then the room 7'6" tall, then the flooring 1" thick, next 2x10 floor joists finished by 12" of concrete block for drainage space.
I then worked it up to make it 12' wide with the 2x6 walls on the inside of this span. I added a normal 32" wide storm door and a landing for the door to swing out. There should be a landing if the door swings in so that you have some place to stand as you open/unlock the door. Standing up on the stairs would not be safe or appropriate.  The the stairs with a standard 7 3/4" rise and 10" treads. I also projected up the 6'8" clearance line for the head height of the stairs.
This gave us the total length of the hole and the opening size for the are where their will be no soil over the stairs.

If it was me, I'd fence off the entire spot so that there would never be any possible way for a tractor to ever roll over this shelter. You're going to have to fence off the stairway opening so that someone doesn't walk into the open hole at night or any other time for that matter, so why not just include the area over the shelter and eliminate the risk of the tractor ever caving it in.

Now, having said that, if the storm shelter is going to be fenced off so that a tractor can't drive over it, then you could make the ground cover less thick and that would mean fewer stairs and less overall ground area to be used up by this shelter. These are just some of my ideas.

I haven't been to those sites listed above to research anything there, but I'm sure they have some good information there.

Jim Rogers

[lynches lumber]

Jim_ Youre right on the money with my plans. Actually their will be a porch over the stairs with a flip up door. The door will be counter weighted so you dont have to wrestle the weight of it when your in a hurry to enter the shelter. The door into the shelter will open into the shelter. Its alot easier to open in than out especially if youve got a petrified wife pushing you in. I really would like to be able to drive the tractor across it if needed. What would I need to beef up in order to do this? Thanks.

[Jim_Rogers]

Well, soil weight per cubic foot or yard would help.
Also the weight of the tractor.....

Jim Rogers

[lynches lumber]

Jim_ Figure about 6500 lbs with tractor and mower. The dirt, well its heavy. Seriosly I have no idea. Were in the red clay district if that helps any. I was kinda thinking after the top backfill of clay was compacted it would help with the load. ???

[Jim_Rogers]

lynches lumber:

What type of wood would you be using for the post in the middle holding up the beam that is holding up the ceiling joists.

also what type of wood for the ceiling joists?, beam? 2x6 studs?

Jim Rogers

[Thehardway]

How long do you want this thing to last?  Imho you are going to spend a lot of time digging and building and have little to show a few years from now. The termites ants and bugs are going to have a feast on this thing unless you have some really bug resistant trees around to mill. Better plan on  using the PT lumber for sheathing as you won;t be able to replace it and use the 1X for the flooring where you can replace it every few years. At minimum you will need galv. nails. All walls will need to be sheathed and assembled above grade and then dropped in and assembled unless you dig your hole large enough to work in outside the walls which represents twice as large a hole and a lot more back-fill and compaction.

Do you have access to a machine to do the digging or will this be hand dug? Do you plan on digging this thing all the way down to 10' or are you planning 5' deep and using the removed 5' of soil for berm and cover?  This would save a lot of labor, give you better drainage, less stairs and you wouldn't have to haul off site the dirt you dig out.
Working in any hole deeper than 4 feet you are risking getting killed by a cave in unless you bench it back or have a retainer in place with escape route.  Not much sense in building a shelter to stay safe if you get killed building it.    Your soil is going to place a tremendous amount of inward pressure on your walls as you back fill and compact around it.  I believe 1x on diagonals will not  be sufficient to hold this pressure and it will continue to build  up over time, especially if driving tractors over it.  I would leave the moisture membrane out of the floor, it will trap moisture and condensation rather than protecting you from it and keeping things dry.  If you are in clay, it will never dry out inside and the sump is not going to run in a storm if you lose power so you could drown in your hole. :-\

If it were me, I would dig a 12X12X 5' hole then drop in a large corrugated culvert, an old steel tank, or perhaps a concrete septic tank in it. Then I would berm it and cover it. This will hold up much better over time, offer better protection, be more comfortable, and probably not cost any more when its all said and done.  You could then use the lumber to build an attractive entrance and a nice "doghouse" above ground.
If your like me, your "dogouse" above or below ground will accumulate so many unfinished projects, there will be no room left for you and the family during a storm.

I know once we get an idea it is hard to be convinced it is not safe or doable but this sounds like one idea where the thinking cap was a little to full of home brew when it was conceived.  I'm betting the idea loses some of it's glamour as your back gets sore and the wife complains about that big hole full of water in the front yard that has frogs in it chirping and you have to bail it out every weekend before you can get started.  My thinking cap says this needs to be built out of solid timbers (Picturing a railroad tie style bridge) or something other than wood or else it will be a death trap and not very usable.  You might want to search PT foundation wall plans.  I know there were some engineer approved designs back in the 80's but they weren't very popular for a number of reasons.

[lynches lumber]

Jim_   The majority of the lumber will be SYP. I do have some red &white oak that could be used for the beams if necessary.

[lynches lumber]

Hardway__ First of all, my alias is hardhead. Moma always said I had to learn things the hard way. This should be no different. I do have the equipment to do the excavation. I do have a fear of cave in during construction so it will be dug out large enough to take care of that. The location of the shelter is uphill. Any water that enters the crawl area will be drained.The sump pump is only for backup. I know there are members of the structure that are going to have to be beefed up from the original conception. I have a top notch professional working on this as we speak. As for the moisture, the entire structure will be sealed with 60 mil epdm. Ventilation will be taken care of. As far as the metal structures your suggesting putting in th ground, I would be concerned about rust. A friend of mine has a septic tank buried. Can you say clostrophobic? Finally, I dont drink so we cant blame this on that. :D

[Brian Moore]

Hey there, newbie here.   What about one of those metal cargo containers?    I would think that you could buy one cheap and with a little welding and reinforcing you could have a solid storm cellar.    Yes it would eventually rust but I would think it would out last a wooden structure underground.    Like I always say my opion is worth what I charge for it.

Good luck

[lynches lumber]

Brian__ Welcome. Youd definately would have to reinforce it. Had a fellow down the road from me had one that he bermed sand up against it and it caved the sides in. If the wooden structure is completly sealed and ventilated against moisture why wouldnt it last?

[beenthere]

lynches.
Probably because it cannot be completely sealed.
I'm not of the mind to try to talk you out of this plan. In fact, I'm anxious to see you give it a go and fill us in on the details, as well as the outcome.

[lynches lumber]

Beenthere______Please explain why it cant be sealed to keep the water out.

[Brian Moore]

I too am not trying to talk you out of this.    However, you said that the ground was Clay.   This to me says high moisture content.   I would be worried about this stucture 10+ years from now.   The only way this could be "completely" sealed would be not to put a door way into it.  So there will be an edge somewhere.   If I were doing this I would surround the room with gravel to make sure that the water would be able to drain.     One other thing that I would do is to dig the hole and place "x" number of inches of gravel in the bottom.    Then I would let the hole stand for a couple of weeks (yes I said weeks).   This will let you see if the hole will collect water or let water drain.    You said your house was on a slab.    This worries me as the water table may be too high?    Me I just like to keep my wood above ground.   

[lynches lumber]

Brian___You are right the water table is high here. That is the purpose of the drain system in a crawl area under the shelter. Yes gravel will be used. My house is on a slab, not because of the high water table, but because it was suppose to be my shop to start with. But thats another story. The entrance to the shelter will be sealed up to the point of the door which will be under a covered porch. Dont feel like I think youre trying to talk me out of it. I want all the worst case scenarios so I can deal with them before I begin or abort this endeavor.

[ljmathias]

Not being one to hold back my opinion, I'll try to talk you out of it if no one else will, and that's based on personal experience.  My daughter is the owner (supposedly- divorce decree but title still in ex's name) of a house set into the side of a hill.  Soil is good ol' southern red clay, the worse sub-surface there is for water problems.  The house has a basement that is fully underground uphill, fully exposed down, so it's really only a half or sloped basement.  Don't know the original in-ground specs, but before they bought it, thousands of dollars spent on digging up the clay around the entire part of the basement that was underground, sealing it, putting in gravel and drains and adding a french drain system on top to keep water from flowing down the foundation walls.  All said and done, it leaks like a sieve, always has and always will.  Conventional wisdom in the south on basements is simple: don't!

Ok, so now you're going to put something underground completely that you want to keep dry: can't happen.  No matter what you do, water finds a way in and you'll have a structure sitting in and surrounded by water just wanting to seep in and help the mold, termites and fungus get at whatever's there.  God built nature that way, and everything works according to plan: stuff in the ground rots, rusts or molds.

Ok, so that's my opinion.  I've got a son who also believes he can overcome nature by dint of will, and there's no question it can be done.  Only question is cost and heartache required.  He's wanted to build a house with a basement for the longest time, and I just never had time to help him get started.  Built a small house for Granny who then passed away so I gave it to him and his family- no basement and they love it although it's getting a little tight with four kids now.

Anyway, hope no offense taken- just my opinion.  Have fun and be careful down in that hole- Mother Nature hates holes and tries her darnest to fill them in with something, so don't let it be you.

Lj