underground shelter

[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

[Thehardway]

OK, so you have a machine to dig the hole, that takes away a good part of the labor (unless it is like most machines and requires a couple days of non-stop labor to get it going and then it takes a break every 2 hrs. just like all good American labor)

Water will not drain out of clay soil even if you have drains, sump pumps and somewhere to go that is lower. Clay naturally collects moisture and holds it (think about clay pots) unless there is something actively drying it (ie. sun, furnace, heater etc.) but I assume you know this and have a good plan to reverse the natural  characteristics of clay and make it like unto sand... 

Next comes the wood. Unless chemically treated, White oak will only last about 15 yrs. in soil contact provided no bugs choose to munch on it. Red oak might last 2-3 years and SYP might last about the same.  I would not build this structure of untreated red oak and SYP unless you want it to be your last proverbial "pine box".  All wood that cannot sufficiently breathe and is exposed to high humidity levels  (like would be common in a underground box sealed watertight with 60mil edpm) and has no active mechanical ventilation, will be subject to becoming food for fungus and mold and will rapidly lose its strength.  A borate solution soaked into the lumber might help preserve and it would still be occupiable, most other DIY preservatives such as used crankcase oil, diesel fuel, creosote etc. would all make this sealed structure toxic and stinky.

For retaining walls I would use 8"X 8" borate treated white oak or Black locust posts set into 2' holes drilled in undisturbed earth in the bottom of the big hole at 2'OC. Diagonally X brace them inside with a 2X6, then horizontally plank them on the outside with 3"X5" T&G SYP that has be dried and then treated with a borate solution.  Planks should be nailed with 6" galv. ringshank pole nails.  After this is done, hot mop the outside of the entire assembly with about 3 coats of asphalt based sealer, then apply your membrane.

Assemble the top of the roof of the structure by using 10"X10" timbers that are notched and morticed at ends to receive posts with tenons on the upper end of each post. These will serve as your bearing beams and your joists.  These should also be planked over in like manner as the walls and then hot mopped and sealed with membrane applied and lapped over the wall membrane.  After everything is sealed, apply a moisture resistant insulative barrier such as EPS foam on the outside (this will help prevent condensation)and will prevent the membrane from being punctured during back-fill and compaction operations.

Once complete, back-fill the perimeter walls with pea gravel up to the top of the walls using 6" lifts evenly distributed around the structure.  Run another layer of membrane over the roof which extends beyond the wall perimeter and the pea gravel bed out to undisturbed soil.  Now carefully place you backfill clay soil over the top of the structure makeing sure it is free of stones or other debris which could puncture the membrane. 

Now that you are "dried in" place a 2" layer of gravel on the floor, put a 1" layer of EPS over this and then run some 2X sleepers over the foam on 16" centers.  Plank this with 1x for flooring. It is a "floating floor".

This should give you a fairly warm, comfortable and durable shelter that would last for maybe 25yrs.
If constructed using these methods I would feel reasonable comfortable entering it.

Disclaimer!!!  This is not an engineer approved design and I am not an engineer.  This is a fly by the seat of your pants approach based on my experience with PT retaining walls, underground communications vaults, bridges, manholes mines, etc.

I would also install a sump pump and a ventilation system as well as lights.  I believe this would support the weight of your tractor as well but can't verify.

[Kansas]

Would it be possible to build an above ground structure strong enough to stand up to a tornado using wood? It wouldn't have to be that big if the sole purpose was to protect in really bad weather. That would eliminate all the water and moisture problems. I know they make such a thing out of concrete.

[ljmathias]

They also make them out of steel- saw an add in the local newsletter for one 8X10 for $3999...

[Larry]

Would it be possible to build an above ground structure strong enough to stand up to a tornado using wood?

Yes, well the government says it’s possible anyhow.

Building a Safe Room For Your Home or Small Business 

No matter what style shelter ya build this is a great reference guide and it's free.

Kathy’s walk in closest looks like a...walk in closet, but it is a tornado shelter built out of wood with some steel.  The give away is the steel door inside the conventional wood door.  Our state kicks back $2,000 if built according to FEMA plans.  I haven’t sent in my application yet.

I built it with the reasoning we ain’t gettin no younger.  It may not be possible to jump up and run to an outside shelter in a few years.  Can’t say that I would want to do that now, especially in the middle of a stormy night.  Yes, our closet is wheelchair accessible.

[den]

http://www.ag.ndsu.edu/aben-plans/5948.pdf

http://www.ag.ndsu.edu/aben-plans/6376.pdf

http://www.ag.ndsu.edu/extension-aben/buildingplans

http://www.public.iastate.edu/~mwps_dis/mwps_web/frame_p.htm

[rbhunter]

I am not sure how it is done but my granfather build a cave with a concrete and rock top back in the forties I think it was mixing concrete by hand over several months. It was strong enough that one of my uncles drove a farm truck over it loaded with grain  and stopped on top of it. It was built outside of the house into the side of a small hill. There may be someone on here that would know how to build something like this. The cave is still standing to this day and usable. I was in it one time during tornado warnings when I was younger (I know we had at least 5 adults and 5 elementry kids in it that time). But I don't remember much about the inside but it was not real thick on top but was rounded.  It was also used to store the potatoes that was dug each year. I know we would unload two or three wagon loads of potatoes into it. I may be able to get a picture the next time I am back in Kansas but that may be a while.

[Ironwood]

I am contemplating a similar project with concrete and back fill, but this has lots of drop off the side of a hill.
 Ironwood

[Woodchuck53]

We have been thinking along these same lines and here is what I have rednecked engineered.

The next and last addition on the home is a master bed room down stairs. The bosses walk in closet will be double layed up 8x8x16 block with poured 6" reinforced concrete between, on slab of course with 6" slab ceiling. Accessable from the bedroom as well as the main part of the house thru the kids old bath room. That's the plan because no wood would stand up to the the bugs here in central Louisisana.

It may be a waste but it seems the storms are more violent and come more often. Piece of mind and all that. Stay safe.

[clww]

I'm incorporating a very small (6' X 6' X 7') safe shelter room into the basement of our cabin we're building. Using the two existing corner walls of the basement, the other two sides will be .25" thick diamond plate, bolted together. Outside walls are 10" thick filled with concrete plus completely underground. For the ceiling, I plan on adding a 12" slab of reinforced concrete bolted to the walls every 12". The door will be a salvaged hatch from a ship.

[Ironwood]

I  am working on two plans, one short term quick and expedient 1000' from our home (current work area) and EASY to bury something. The second will be in a couple years and close to our home. I agree with the severity and frequency of weather getting to be a concern, but I am also thinking about NBC shelter.
 
Ironwood