Building and Using a Precast Septic-Tank Root Cellar


buried root cellar

I mentioned building a root cellar in my introductory post, but I thought readers of Mother Earth News would be interested in a more detailed description of making and using it. I based the design on this plan, which involves modifying an (unused!) precast septic tank. When I decided to join my brother Ed in growing all my own food for 2015, I knew I would need a better place to store our root vegetables than the old farmhouse basement, but using using cinder blocks or building forms to pour concrete in place seemed like a bigger job than I had time for. Using a precast 6-foot x 6-foot x 10-foot tank and some materials I had on hand made the job much easier than it would have been, and I ended up with a root cellar that has maintained a stable temperature and high humidity even in the worst of a harsh New York winter.

One of the biggest potential jobs required to put in a cellar, no matter the design, is digging the hole. Luckily, I already needed to rent an excavator for some other things around the farm, and it made what would have been days or weeks of work with a shovel a matter of a few hours. The location I chose is a bank off of the driveway. It’s south facing, which concerned me a little - I thought it might be prone to overheating - but it was the only suitable site within a reasonable distance of both the houses and the garden.

There were a few tense minutes when it looked like the truck that was delivering the septic tank would not have room to maneuver into position, but the driver finally managed to line it up. I’d been expecting a boom truck, which can drop a tank almost anywhere, but at the last minute I got a call from the concrete company saying the tank weighed so much that only their truck with a slide off of the back could handle it. It ended up working out, but it would have been less stressful if that miscommunication could have been avoided.

The tank already had flanges around the top, and these let me put in vent pipes without drilling new holes. I did need to rent a saw to cut the doorway, and there’s no way to overstate how noisy, messy, and tiring sawing through concrete and rebar is. But the most time consuming part of the project was the retaining walls coming out from the door, for which I used cinder blocks I’d stashed over the years. I did a double layer with mesh going back into the backfill to help hold them in place, and all the tamping and dirt moving seemed endless. Now that I’ve gone through most of a winter, I think that the extra labor was worth it. Having the front of the root cellar as buried as possible helps moderate the temperature, and in a cold winter that’s a must.

root cellar retaining walls

3/11/2015 11:29:25 AM

Thanks for an interesting article but I surely would like to see more pics. What does it look like from the outside & the inside. I am looking forward to the next series of articles.

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