This article is about my experience using a shipping container as a mouse-proof cellar. A couple of important notes up front – shipping containers are not designed to have a load-bearing roof. I discovered that quickly while attempting to put a dirt cover over the top of the container. With a small load of dirt on top, the roof of the metal container began to bow. I shoveled the dirt back off of there, and revised my plan as explained below. So don’t do that. Also, it is essential that the container be installed above the groundwater table to prevent infiltration with water.
Here is a bit of my background with cellars: I grew up in a small community in the rural west. My family worked on cattle and sheep ranches. Heat for our home was a wood stove, and we did not keep the stove running at night. We had freezing temperatures indoors at night during the winter time. We did not have indoor plumbing – because water pipes would have broken from the cold. Sometimes, I broke an inch of ice off the top of the water pail in the kitchen. Then got the wood stove going, and put on a kettle of coffee for the morning. Of necessity, we had a cellar because glass bottles of canned food would have broken in the freezing temperatures of an indoor pantry.
This was common farm life in the 1950s. Nearly everyone in the area raised a garden and had a few fruit trees, mostly apples, apricots, and plums. The women all knew how to can the harvests. And they canned the meat, too. Venison, beef, and chicken. They made trips every summer to the fruit growing areas to buy bushels of peaches and pears, and lugs of sweet and sour cherries. They did lots of canning to store food in the cellar. In the fall, the cellars were also handy for hanging butchered meat to let the meat age before processing.
The cellars that I grew up with were excavated by hand and covered over with juniper logs along with willow and straw thatching. Soil from the excavation was piled on top, leaving one vent pipe through the roof for air circulation. However, with only one vent pipe, the air in the cellars was always musty and stale. A double door system was constructed with one vertical door at the cellar entrance and another semi-horizontal door providing access to the stairs leading down to the cellar door.
These structures were sturdy and long lasting with shelving constructed along both sides There was a double row of upright posts along the center aisle that helped support the roof and the shelving. The cellars were generally 8-10 ft wide and at least 15 feet long. In addition to all the canned goods, most people stored a couple of hundred pounds of potatoes and fifty pounds of onions at the back of the cellar. The structures were waterproof and prevented freezing even in the coldest winters.
These cellars, however, did not provide protection from mice and spiders. Both were common pests. As a child, I dreaded trips into the cellar to retrieve food for the kitchen because I had to tear through the spider webs. Even if the cellar had been opened the day before, the spiders were quick to construct a whole new network of webs overnight. So, sweeping aside the webs in the cellar was a real thing. But there was a danger, too. Some of these spiders were black widows. The bite from a black widow is rarely fatal but is horribly painful and often leaves bad scars where the spider venom causes the flesh around the bite to die before finally healing over. I took a flashlight with me because there were no lights in the cellar or the stairwell. The cellar was dark, dank, and uninviting.
Despite these drawbacks, a cellar was a necessity where I grew up. As an adult, I determined that if I ever got to build the homestead of my dreams then I would have a cellar. About 16 years ago, my wife and I purchased a small acreage and built our home there. The cellar was the first structure that we built. It became our dry, mouse-proof storage while building our home. I considered the construction cost for several options including concrete, cinder block, treated lumber, and metal. To my surprise, the fastest and cheapest option for building a cellar was to install a 20-foot shipping container in the ground. (Note: Don’t do this if you have a high water table in any season. Your site must be dry to below the depth of your cellar at all times.)
In 2008, there was an abundance of excess shipping containers arriving in the United States, and I purchased one from a small company that had a business selling and delivering empty shipping containers. Available options included simple modifications such as a walk door and vent holes.
I ordered a 20-foot shipping container (“CONEX”)with a steel walk door welded into the end opposite the standard double doors and a five-inch vent hole in the ceiling near the front and another five-inch vent hole in the ceiling near the rear. The company was selling so many shipping containers that they were able to coordinate transport with another container headed my way, and save on delivery by sharing the transport cost by truck. We paid approximately $5,000 for the 20-foot container with a walk door and two vent holes delivered to our property.
The first step of installing the shipping container in the ground was to excavate a trench for the container. We already had an operator with a 550 Caterpillar front end loader on site to dig our pond and level our building site, so it only took a couple of extra hours to excavate a trench with a ramp to accommodate the container. I had the loader operator put down 12 inches of washed gravel in the bottom of the trench for drainage and then he slid the container into the slot. The standard double doors form the back wall and are not accessible in the finished cellar. We coated the exterior of the container with black mastic (roofing tar) to prevent rust and then put two inch thick blue board on the roof and sides which stuck nicely to the mastic. I back-filled along the sides with soil and tamped it down. I doubled the thickness of blue board on the roof as insulation.
As I mentioned at the beginning, I made the brief mistake of shoveling some soil on top of the cellar, until I noticed the cellar roof beginning to bow and took the soil off. Shipping containers on a ship are stacked high, but they are stacked directly one on top of another, and the load is held up by the corners, and not the roof.
So, to finish the roof of our cellar, we bridged the walls of the shipping container with a concrete slab. We built an 8 inch deep form for a flat slab with lots of rebar and mesh wire on the top of the blue board that was on top of the container, and made sure that the finished concrete slab would extend past the walls, so that the weight of the roof would rest on the container walls.
Before pouring the concrete, I shored up the inside of the container in several places with 2×6 lumber similar to the way a mine tunnel is supported. I placed a vent pipe in each of the vent holes. The pipe at the rear of the container drops to about six inches above the floor and the vent by the access door only penetrates about 3 inches. This configuration allows for passive air flow (cold air sinks and warm air rises).
I put fine screens on both vents to prevent spiders and mice from entry. I also placed cone covers on the pipes to stop rain and snow from entering. Once the concrete was cured, I pulled the lumber shoring from the interior and the roof of the container has not sagged.
Later, I built a shed over the location of the cellar and the stairwell. The concrete slab is a useful floor inside the shed, and the shed helps to insulate the cellar and the stairwell from the heat of summer and the cold of winter. During the summer, the cool night air drops into the cellar through the vent, expelling the warmer air. In the winter I plug the longer vent pipe at the top to prevent too much cold air from entering. When the summer temperature outdoors is about 100 degrees F, the temperature in the cellar is around 60 degrees F. When the temperature drops to 46 degrees in the fall, I plug the cold air pipe.
The winter temperature in the cellar stays in the 40s when it is well below freezing outdoors. My wife painted the inside of the container with white direct-to-metal paint so that the interior of the cellar is brightly lit with a single 60 watt light bulb. We live in an area with generally very low humidity, so condensation has never been a problem.
We put free-standing Gorilla Rack storage shelves along both sides of the cellar except for an area of blank wall where we stack five gallon buckets of dry goods with Gamma Seal lids and 5 gallon water containers. We store dry goods in bulk in the cellar along with produce my wife cans from our orchard and garden.
I constructed the stairwell to the cellar with 6×6 treated lumber with corrugated tin lining the walls of the stairwell. I did not pour concrete steps but instead used the 6×6 treated lumber as forms for each riser and back-filled them with gravel. This has worked well and seems to be holding up just fine. There is a light bulb above the cellar door that lights the stairwell. In 16 years of use, and obsessively keeping the walk door closed, our shipping container cellar has proven to be mouse-proof and spider-proof. We enjoy using it.
A few notes on cellar use: We enjoy growing and storing Yukon Gold potatoes, because they have a short growing season, they store very well through the winter, and delicious to eat mashed, baked, or fried. To avoid the conflict of storing apples and potatoes in the same space, my wife simply cans the apples that go in our cellar as apple pie filling, apple sauce, and apple juice.
If I had it to do over, I would put in a 40-foot-long shipping container to hold twice as much volume of preps and serve as an underground bunker in case of disasters of the worst kind.. As it is, my wife has our cellar very well organized and seems to always know exactly where to find everything when we need it.
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