underground shelter

[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