Nine Letters Re: Questions on Underground CONEXes

Tuesday, Oct 2, 2007

Dear Jim And Readers,
As Jim said, [CONtinental Express] CONEX containers are not designed to be buried. They will stress out and leak. (I know of an [illicit] drug lab that was in a buried Conex container, it did not do well.) Having said that, a better choice is a buried culvert pipe. You can use 8 foot or 10 foot diameter. Remember the Roman Arch. "Earth Arching" will make it strong. There are a lot of buried culvert pipes in the world that have survived decades of heavy traffic. Weld end caps on the ends of the culvert pipe and use smaller diameter pipe for an entrance. It is easy to put in a wood floor to store cases of #10 cans underneath the floor. How to bury it? Go to your friendly Caterpillar Rental Store. Rent a backhoe or a excavator ("Track hoe"). They will deliver. Never operated one before? No problem. They will give you a quick lesson. By the end of a day of digging you will have it down. Remember not to have your vehicle or house within range [of the bucket arm] when you first start out!

We also dug a few holes and dropped 36" diameter used culvert pipe vertically about 8 feet deep. Back fill it with dirt and with a base of railroad ties, you can build a dandy outhouse that will hold lots of Schumer in case of emergency!

As far as building a house we use Structurally Insulated Panel (SIP) construction. Structurally Insulated Panels are three times as strong as stick built homes for earthquake. You can go all the way up to a 12" thick panel that exceeds the insulation value of a straw bale house. Better insulation means less fuel to heat and cool your house. You can get them in a kit. I would never build a stick built house again. You can get the walls up in a day or two.

Keep up the great work that you do, Jim. - PED


Burying a CONEX container will collapse (or in my case partially collapse ) the side walls of the container. If you use insulated concrete forms (ICFs) and pour a modest side wall and reinforce the top using the incredibly strong corners as support then you can bury one to at least four feet. The insulated forms will greatly mediate condensation problems but the site must be well drained. All in all it would have been much cheaper for me to just build a concrete storage site but I got into the "In for a penny,in for a pound mindset" and things just got out of hand. My next underground facility will be a large septic tank waterproofed inside and out buried to stash very long term food and munitions. The condensation problem is exacerbated by opening the doors and letting warm moist air into the very cool dry interior of the Conex. I suppose that I could build a double door entrance and greatly reduce the condensation. The idea of successfully burying a CONEX still appeals to me if the cost and effort could be reduced. - East Tennessee Hillbilly


A thought: Containers are stackable, but load bearing is in question.
A ground level container on a property is hardly uncommon.
A second container [hidden] underground beneath it, acting as support for the first... - The Hushmailer


I have personally done such a project. It was quite involved. I wouldn't do it again. between the cost of the container $1000 cheapest available from Newark NJ, then transport $600, then the railroad ties and wood to form for a concrete roof, then steel, then $800 for crete; the because the sides bulged in when backfilled; I had to mineshaft it. $1000 worth of lumber(large dimensional native sawn oak) and two days of my time. The CONEX must be placed on a level reinforced footing: or it goes out of square easily and doors won't shut.
If I had it to do again: I'd simply rent the forms and pour the whole structure out of concrete. I never spanned more than 8' anywhere in the project due to railroad ties 8'6" length ($4 each) and the fact that they have to support a 6" concrete roof and 2-to-3 feet of fill.
The corners aren't the whole story in CONEX containers: the walls are integral and support weight. The roof is the flimsiest thing: I suggest anyone who thinks they can bury one unmodified to merely walk on the roof before they buy it: when it buckles under your own weight that bell should ring in your mind. My design utilized lots of free billboard vinyl tarps and professionally cleaned 12,000 gallon double wall fiberglass fuel tanks (already designed to be buried, plus they are free).

If I haven't dissuaded anyone yet from burying a CONEX and they want to go ahead anyway: some sound advice I would offer is be wary of what [type of] CONEX you buy. I tried hard to buy a galvanized one; but [they are] hard to come by and very pricey as they are usually used for a "refer" box with attached refrigeration unit. Secondly don't forget to buy some zincs for sacrificial anodes to slow corrosion. And most important ; seek out a CONEX made of Corten steel [aka Weathering steel]: it is a very special steel alloy. Most of the good European based shippers like Hapag-Lloyd, P&O, et cetera use them. Bridges that will never be painted in the US utilize Corten steel: it [surface] rusts immediately; but then corrosion slows to close to nil for some very long time. Google it. The container I used was made from Corten, although it was nearly 18 years old; it had almost no rust. I have seen some half that age that were turning into piles of scale.
After I buried mine I coated it with liquid asphalt [aka "asphalt emulsion"], then tarps, then isocyanate roof insulation board I got for free from local roofing supply houses (they left them outside for too long turning them yellow and no longer salable), then more tarps then careful backfill. Burying the CONEX is easy; but what do you do for an entrance? That is where you will spend considerable thought, time, effort, and money. I have no issues with condensation. here we we are in the Northeast; temperature stays a constant 53 degrees inside there year round: ideal for food storage and other critical goodies. My main reason for its construction: hidden, insect proof, rodent proof, secure, water tight. Hope this info is of some significance. - John E.


Regarding camouflaging vents from an underground storage/living area, there is are some pictures and ideas here [at the Walton Feed web site]... along with another alternative to the CONEX idea.
- JFC in the Ozarks


Hi Jim.
I saw the post about shipping containers underground. I don't have data, but our real-world experience (and our builder has hundreds of in-ground installations of steel shelters--all engineered by a certified structural engineer) is that any shipping container going underground as is will fail and does--period. It's very dangerous and foolish to think that it can be a shortcut to providing a safe place to go in time of need. Above ground would be a different matter as there are not the lateral subterranean forces at work there. But similarly, I would not want to be in one above ground, even if it was anchored in concrete in a serious wind storm. Think mobile home. And of course, above ground is not going to do you any god in terms of being a fallout shelter.

Reinforcing the container/structure every two-three feet on each of the structure's surfaces with heavy gauge channel bracing and possibly adding steel plate around the walls may do the trick--but that is no easy or cheap job. And of course, you also need to be talking about moisture sealing/corrosion-proofing the structure externally to be sure it won't suddenly fail you a few years down the road, even if you do all the needed buttressing.

Another alternative would be to use the shelter as a form for heavily rebarred concrete to be poured around and over it--again with some reinforcement to ensure the wet concrete does not cause a structural failure.

In my experience, those who post on the internet of plans for shipping container shelters do not have real-world qualifications in the matter.

This much I can plainly tell you that should tell a lot--we would (as would our competitors) love to be able to offer cut-rate shelters to customers if it could be done, using shipping containers. But it can't be done economically. If you are actually looking for a safe refuge, do not do this. Shortcuts in building/engineering cost you in the long-run. At the front end, such a DIY project might save you a few bucks, but not that much over what is available out there that is certified to do the job you need it to do. Longer term, it could end up costing you dearly.- Vic at Safecastle

About two years ago I "planted" a couple of CONEXes for use of as a goat barn for a lady acquaintance of mine A few things to consider:
1) If it's damaged, fix it! Any ding, dent or gouge can (and will, over time) precipitate a stress riser, and the wall may collapse, usually in spectacular fashion;
2) The walls need to be braced from buckling inward. If they want to bow outward, not a problem. The earth packed around them will hold them in place;
3) Corners are strong; tie the walls to them (we used 3"x3"x0.136" tubing for bracing, and welded it securely to the sides). Same going with passages cut between the containers;
4) Set the containers 1'-2' apart. The ensuing "box" you build to bridge that gap as you cut doorway will serve as a pilaster to strengthen the middle of the structure, both laterally as well as in compression (holding up the roof). Also, make your doorways all the way to the top of the wall(s);
5) Insulation, ventilation, drainage, condensation: for brevity sake, I refer you to two sources: "Earth Sheltered Houses" by Rob Roy (the old hippie, not the 17th century Scottish patriot!), published by New Society Publishers; Rocky Mountain Research Center. I can attest to the efficacy of information provided in both of these, as the abode I'm sitting in was built using them, and I'm wearing T-shirt and drawers, it was in the mid-30s last night and I haven't built a fire for two days, and that was to bake bread in our masonry brick oven (demonstrating the value of thermal mass; more on that in the books);
6) And finally, using more steel tubing, we built a grid work to hold rebar , and had concrete poured onto the roof (my lady friend wanted a patio garden). Depending on the bracing you add to the roof, you can bury your tin cans as deep as is practical (read with particular interest chapter 8, Earth Sheltered Houses, on "living roofs"), and pay particular attention to proper overall drainage.
Yes, it can be done, it's not terribly difficult, it's really not very expensive (YMMV depending on what work you do yourself), but it does require a lot of planning and attention to detail. Remember, you will be living there. The little dip in the floor may not bother you now, but may drive you nuts the thousandth time you stumble in it. Hope this helps, keep the faith, - Bonehead


[What Robert in New York suggested is] not a good idea. The weight of that much earth would cave in the sides.
Better to carve a hole in the woods, use camo paint and park it [a CONEX, aboveground.].

It would be safer and more cost effective to use steel culvert. My friends thought I was crazy until an F5 tornado leveled Jarrell, Texas

Depending on your budget, an 8 or 9 foot diameter culvert with the ends welded up makes an excellent shelter. Weld angle iron about a foot from the bottom along both sides of the interior. 6 foot 2x12’s then rest on the angle iron to make a sturdy floor. Entrances and vents can be cut and fitted to please. During final touches we had a fully loaded cement truck parked on top.

As is, culvert is not water proof. A coating of automotive under-spray would be nice.

Pricing is by the foot for both diameter and length. Installation is easily handled by a track hoe. - Jon in Texas

Here's some info on the inverted shipping container idea.
The principle of an inverted CONEX as a shelter comes from military use as such. A military CONEX is 8x8x6 and not the conventional shipping container that most people see or have access to. To confuse matters more, the military has also used the same commercial containers since they came out as well, so the word "CONEX" usually attaches some confusion as to what is meant. As far as the Army is concerned though, throughout it's publications on using one as a shelter, it refers only to the GI CONEX (8x8x6). So while you can take good ideas and make them better, the readership should
understand that there may or may not be a difference in actual use between the commercial shipping container and a CONEX.
The purpose of inverting the CONEX is to have the stronger floor become the roof. This is done primarily because it provides better ballistic
Obviously the secondary effect of inverting is that the now stronger "roof" can hold more material for improving on that ballistic
protection. FM 5-103,"Survivability" 10 June 1985, has an explanation and illustration of use of the CONEX as a shelter. There was an earlier edition to this manual that had a much better explanation and actual pictures, but I haven't seen a copy of that edition in decades. Either way it doesn't matter much.
The preferred way to dig one in is to invert the box in a hole that is about half the depth of the box (i.e. 4 feet). Then cover the half that's sticking out with earth, etc. The illustration shows over 5 layers of sandbags, or a great deal of dirt, so they can indeed take a lot of weight.
Remember this is the GI one and not the commercial container, but the same principle would apply. While the FM is pretty shy on details as to how much you can pile on, since most people would not be using the GI container illustrated and would be using a commercial container, any numbers would simply be wrong for that type of container, so it's probably better there
aren't any given to begin with. I wouldn't use this exact method myself.
If I were to use a commercial container, I'd generally follow the Army FM but with some changes. Since you aren't really going to be moving this thing around to keep up with a mobile Army, you can afford to do better site preparation. I'd dig a hole half as deep as the container, and then add in some drainage, such as weeping tiles and waterproofing. Just burying a metal box in the ground may work for a while, but eventually you're going to have a rusted-out buried metal box if you don't do something to protect it.
I'd make sure the hole floor has a slight grade to it, and place the inverted container in the hole with the door at the downhill side. A sump would go in on that end and the weeping tile would lead to the same sump as well. Across the sump would be the stairs leading down from ground level.

Digging into the side of a hill makes drainage easier, but you still need to take steps about drainage. If you don't, you'll end up with a rusted out metal box full of water. Look at the level of work as being about the same as installing a basement and that should give you a good idea of the work involved.
Instead of just burying the top half under a mile of Earth, I'd consider just what the ballistic protection factor really needs to be. You aren't normally going to need artillery or air strike protection. If you do, then
by all means build a better bunker, but most people will simply need to stop [rifle caliber] bullets. Since we only have to stop direct fire, you don't really need anything piled on the box itself unless your site has some other terrain feature that is higher near enough to be used by shooters who would then be able to shoot down at you.
Piling dirt or sandbags directly against/on the box has the advantage of not needing as much material, and easier to conceal. Nothing says you have to do it that way. Since only half the box is above ground, it's pretty easy to build berms, or a sandbag standoff that will give you direct fire protection, and allow movement inside the "perimeter" of the site. It all depends on what's best for you and your site.
You can easily see just how much work and resources could go into one of these sites. But you can start off with just the container sitting on the ground, and slowly improve it over time. Just carefully plan in detail what you are doing and think over all the small details. Don't just take "military wisdom" as the best way for you either. "Think outside the box" there. What works for the big Army may or may not work for you. Often people mistakenly think that if the Army does it this way, then that's the best way, but the Army's job is different and takes into account many different factors that survivalists may not. There are other factors that the survivalist has to take into account that the military doesn't (like cost, first of all).
The inverted shipping container is viable, but it just needs to be thought out. See Ya, - "Doug Carlton"

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