Three Letters Re: More on Retrofitting CONEX Containers for Habitation

In Viet-Nam we used CONEXes as underground electronic shelters. A hole was excavated that allowed space between the side of the hole and the container. The hole was deep enough to allow the top of the container to be below ground. If needed the walls of the hole were sandbagged to prevent collapse. The container and hole were roofed over with support structure and then sandbags where laid over the top. If we were in an area that was subject to indirect fire, two ramps were dug down to the level of the floor with a dogleg in the middle. We would put a layer of heavy rock or I-beams to act as a detonation point to prevent penetration of heavy shell (anything from 81mm up). – Long Goody


I have thought about converting a CONEX for use as a retreat before. I have actually seen several storm shelters in southern Mississippi made out of CONEX containers buried in the side of a hill. As long as there is not too much structural load on the roof of the container there shouldn’t be a problem. If they’re looking for a hardened structure, readers should use reinforced concrete. The relatively thin steel of the container will not support a sufficient load without significant bracing. Also, burying steel below ground is inviting rust unless it’s treated heavily with a corrosion inhibitor.

My background is construction and specifically concrete, reinforcing, and masonry construction. I have done several projects using insulating concrete form (ICF) systems that use a foam type block that is put together. Rebar is then inserted into the void between each side and filled with concrete. The roof is similar constructed. I did some cost analysis and the cost of construction for this is about the same and in some cases cheaper than conventional stick built construction depending on your area. Another less expensive (and less thermally efficient) option is to construct wooden forms for the walls and pour them with concrete (and reinforcing.) Lastly, there is masonry construction. If a reader wanted to go this route, they could either erect the block walls and reinforce each cell or put a rebar in every 2 or 3 cells with the remaining cells filled with gravel. This would save money on concrete and still give a structural, thermal, and ballistic benefit to the walls.

As an aside, all troops and contractors out here in Iraq, with a few exceptions, are all living in what we call CHUs or Containerized Housing Units (spoken “Chews”). These are constructed similarly to a CONEX in that it’s made to fit on and be carried by a semi tractor-trailer. The difference is that it has a window and conventional door in one end and some are set up with a bathroom with shower, toilet, hot water heater, and sink in the other end. It also has floors and electrical system set up to run on 240 VAC. Unfortunately the CHUs here are built by companies in Europe (Cormac and Tyson are the two manufacturers that come to mind right now), but at one time I did find someone in the States that built a similar type container.
Regards, – Brian in Iraq


Dear Sir,
Three observations on shipping containers. According to the tags on the doors, the timber component (the floor to most people) almost invariably is treated with serious pesticide. There are multiple purposes to the pesticide treatments – a) to prevent transplantation of harmful insects around the world, b) to protect the structure of the floor, and c) to protect the contents from infestation
and damage. The treatments are serious both in quantity, being roughly in the range of 1 to 10 pounds of pesticide in the wood, and serious in quality. Even 5 lbs is enough to kill a staggering number of insects. As often as not, these pesticides have been banned in the US (and frequently Europe too). Some cause cancer (e.g.., DDT) while others cause testicular atrophy (e.g., Phoxim). Some take hours of diligent searching to track down on the internet either because of trade names or cryptic abbreviations. Pesticides are at least somewhat volatile and almost certainly will permeate the contents
over time, especially if the can gets hot. Note that the contents can include occupants; caution with food storage in containers also advised, unless strong measures are
taken (e.g., remove and replace the floor with untreated wood). Please note that lacquers, varnishes, paints and plastic sheets are highly permeable to organic vapors.

The point about structural use is well taken. In normal use (weight on the corners), a typical acceptable load for stacking on top of a 40-foot can is 423,000 pounds at 1.8 g (the acceleration caused by [a container ship] pitching in waves). On stable land, this translates into a 761,000 pound recommended weight limit. Roughly speaking, this means they can be stacked 80 – 100 deep if they are
empty, and about 8 to 10 [containers] deep when they are full. The sides are not nearly as strong as the ends, so caution is advised if the stacking arrangement is nonstandard.
Pillars can be placed strategically inside if needed, but they should be reviewed by a skilled structural engineer.

With all that said, it is difficult to beat the value of these mobile structures. In our area, a 40-foot high cube can be obtained for about $2,500 in reasonable condition and $3,000 for good condition. We are seeing strong attempts at increased local government regulation, in part because they have become so popular. In one case, the authorities seek to regulate them as buildings, even though they are
customarily used in commerce for storage and transport of goods. Sincerely, – John Galt