Grain Bin Root Cellar

Posted by Tom Fischer on

As I look back on the farm in Montana I think about some of the ideas that we were able to bring to life. One of those ideas was a root cellar made out of an old grain bin. I figured the strength of the circular design would allow the structure to withstand the force of the soil pushing against it like a culvert does buried under a road. No bracing required, just careful backfilling and a thick layer of tar on the outside for waterproofing. I started asking the locals if they knew of anyone wanting to get rid of a grain bin. I got lucky, and for $200 I was able to disassemble one in a nearby town and bring it back to the farm. I brought a generator, a drill, some scaffolding and a can of spray paint to mark the pieces. The bin was 18 feet in diameter by 12 feet high, a lot bigger than I needed but, what the heck, it was only $200. I brought it all back to the farm including the circular blocks for the foundation, bonus! Fortunately we had a skid steer with digging teeth on the bucket, so I started digging out the location. I decided I would only make it 8 feet deep, for 8 foot walls, and use the rest of the panels for something else on the farm, you'll see those on another project.

After a lot of digging in the rocky soil I put the floor down. I located the center of the hole as best as I could and pounded a piece of rebar in to use as a guide. I smoothed out the soil and put the foundation blocks in, leveling them with a line level from the rebar. I filled the blocks with some pea gravel to help with drainage, and had a large number of rocks piled outside of our growing field at my disposal for the floor. I had raked our field with our skid steer with a rock rake attachment earlier that year. The rocks along with the pea gravel would help drainage if it ever got water inside. Once the floor was done it was time to start putting the walls up. With Jackie's help they went up quite easily, as the marked panels made it a no brainer. We went 4 panels high making the walls 8 feet high. OK, that was easy, now how am I going to make an insulated roof?

I had some 1x12 boards that I was able to pick up from a saw mill down the road that I used for rafters. The hard part was figuring out how to make them the exact shape of the grain bin roof. I bought a used trailer rim, without the hub, to join the rafters on top. Holes where drilled into the hub and then I used decking screws to connect the wood. I worked out the angles to cut the rafters and began mounting them. Could've used a sky hook, as the first few were difficult to mount trying keep the hub balanced in mid air. I guess it worked out as I was able to get them all mounted. The bottom of the rafters connecting to the wall and rested on some 1-3/8 inch chain link fence railing that I had bent to go with the curvature of the wall. (This bender was from used to make greenhouses.) 
I had some real thick UV coated white tarp material that I used to attach to the bottom of the rafters. I first stapled it, then screwed 1x2 boards to the rafters to beef it up. The top center was crowned with a glass lamp shade that I got at a thrift store, and connected it with a circular piece of plywood from the bottom. The lamp shade could be used as a sky light later if needed. I kept it dark to keep the root vegetables from wanting to sprout. A big thing, at that time, was using straw for insulation, so I picked up some bales from a local farmer and got to work. I filled the spaces up with 12 inches of straw and put the grain bin roof over top. It fit pretty good considering trying to cut the rafters at just the right angle took a lot of math skills, mine were rusty at best. I tried my best to make things tight in the roof to help keep the mice out, but the ribs in the roof and the thin metal made it a challenge.

Next came the entrance. I had thought about building a vegetable washing area of even a walk in cooler on top and having a stairway going down into the cellar allowing it to be backfilled all the way around. Being built on a slope to the North, I decided to do a double door entrance. The entrance would be insulated as the grain bin door was just thin metal. I was going to be dealing with straight walls so I had to think about bracing them to keep them from caving in. I had some heavy duty cabling that I was able to bury out from the walls with anchoring in the dirt. I didn't have treated wood so I used tyvek and tar to protect the wood. The roof and front door panel was insulated with fiberglass. From front door to grain bin door is about 8-10 feet. I also placed a 100 amp breaker box in the entry to run the greenhouses, walk in cooler, root cellar light and plug.

I put a thick layer of tar on the outside metal and wood, put some gravel and rocks along the bottom, and started carefully backfilling. We started storing vegetables in there for our CSA customers during the summer, and in the winter for us. I was very happy with the results of this root cellar. I don't know how the walls would hold up if the soil was not rocky, but it was built in 2008 and has held up for about 12 years so far.

I talked to the people, Vernon and Ellen, that live there now and they have graciously shared how the grain bin root cellar has fared all these years.
Vernon wrote, "The grain bin root cellar is really cool.  Very inventive and it does regulate the temperature.  I don't think we have ever had anything freeze in there.  The biggest problem we have had is mice.  We have had them chew through a box of wine even.  I know I don't have the door mouse proof and I have often wondered how you put the roof on and if there is a way in there?  One other issue is the snow piling up in front of the outside door.  Ellen wants me to put a covered  entrance on it.  When we first got here and figured out that we were not going to try to sell produce, I thought I would run some electrical outlets, better lighting and use it for a music/crafts room.  Can you imagine the acoustics?   It does serve well as a root cellar, if you put everything in totes, with locking lids and holes drilled for ventilation.  So, just a couple things you could improve maybe.  I remember how it looked when you first built it.  The floor was lovely and I know it was a lot of work getting the stones to fit and filling in with gravel.  It is a very nice piece of work." Ellen added, "The temperature ranges between 44-46 F in the summer, and 36-38 F in the Winter."

 Hope you enjoyed this article and wish you the best at storing your abundant crops through the winter! Tom

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