How to Make a Root Cellar
Underground Root Cellar
Making an underground root cellar was my fall project for the year 2010.
This article shows step-by-step how it was designed and constructed, from the planning stage to the final result, including information on drainage, ventilation, and insulation.
I'll explain the mistakes I made and how they were corrected (or how I learned to live with them!).
Planning the Root Cellar
I spent many hours researching and planning before I decided what type of root cellar to build and where to put it. And then spent some more time designing it. I relied heavily on information from the book by Mike and Nancy Bubel and also did some research on the Internet. Root Cellaring
There are many different types of root cellars and many different methods of building them. Here I'll just be describing my personal experience in building one with access directly from the basement.
Information about other types and methods, including some simpler and less expensive ones, can be readily found in the Bubels' book or on the Internet. I've provided some links at the end of this article.
Important Elements of a Underground Root Cellar
Size. Make the root cellar large enough for your future needs, since it cannot easily be enlarged in the future. I made mine large enough to put shelves with a depth of 18 inches around three sides and was very pleased with the result.
Good drainage. You'll want high humidity, but not so much moisture that you have standing water or excess condensation. If possible, locate the root cellar in an area that naturally gets good drainage. Ideally, it needs a perimeter drain or drain pipes placed inside.
Ventilation. It's important to have an air intake vent as well as an exhaust vent. This keeps things cool by allowing cold air to enter the root cellar and warm air to exit. This cross ventilation also removes any excess humidity and the ethelyne gasses that are given off by ripening produce.
- Temperature. The root cellar must be kept cool enough to preserve the vegetables and fruits, but not so cold that the produce freezes. The soil around and above helps keep the temperature more constant. Vents bring in cool air from the outside when needed. Insulation makes it easier to keep the coolness in.
- Humidity. The ideal humidity ranges from 80-95% for most vegetables. The best way to keep the humidity high is to have a dirt floor. There are some vegetables that require lower humidity, such as winter squash, and these should not be stored in a root cellar but rather in a drier place.
My first thought was to use an idea I found on the internet: buy a new septic tank, cut a door into it, and put it in the ground. However, I knew I wanted a dirt floor, so the bottom would also have to be cut out.
I called a local company to discuss this idea. They told me it would cost me less to have them build a precast concrete structure without a floor than to try to modify a new septic tank. (This didn't end up being the case.) Unable to find another company to help, I decided to go ahead with their suggestion.
I decided my root cellar would be 8' x 12' on the outside, if I could find a place in the ground to put one that large. So I drew up some plans, including the location of the door and the location of the vent holes, and sent them off to the concrete company.
My next decision was where to put it. It was important to me to have access directly from my basement. The bedrock is very close to my basement walls in most places. In other words, you don't have to dig very far before hitting that ledgy rock. And I needed a hole that was about 6 feet deep!
I hired someone to dig an initial test hole, and assuming we found a place to put the root cellar, to also set up the drainage pipes, and otherwise prepare the site. The photo shows him taking the first scoops of dirt out of the ground. I was so excited!
We were fortunate in that this first spot I chose, which was on the north side of the house, ended up being deep enough. There was only one place where we hit bedrock and we were able to chip that away.
Locating a root cellar on the north side of the house is ideal, since this will help keep the sun from warming the soil above it and thus keep the root cellar cooler.
The hole has been dug! It was tricky because my back steps are a few feet to the right of the hole and a retaining wall is just to the left. It took a lot of careful digging to avoid the collapse of that retaining wall.
Some soil did fall out from under the steps, but a new concrete footing was poured under the post for the step and things were set straight.
After the hole was dug, the next step was to set up a drainage system so water wouldn't collect in that area.
Part of the perimeter drain for the house (the white pipe parallel to the house) was replaced so there would be places to attach drain pipes for the root cellar. In this photo, you can see the drain pipes attached.
The ground was made level, then "hardware cloth" (a mesh-like screening) was put down to keep the mice and other little critters from burrowing in.
Next, some crushed stone was spread on top of the hardware cloth. The rectangular "tiles" were used as footings to distribute the weight more evenly.
The company that fabricated the root cellar wanted us to use larger "tiles" for footings, but there wasn't enough space for them due to the bedrock being so close. Since one end of the root cellar would be sitting on the footings for the house foundation and one other corner would be sitting on bedrock, we felt that this would be sufficient.
Around here, you have to hire a separate company to cut the opening for the door in the concrete basement wall. (Or do it yourself!) It was a much more complicated process than I had expected, but these guys were real experts.
The concrete was taken out in two chunks: first the upper and then the lower part of the doorway.
Water was applied during the process of cutting through the concrete. Fortunately, I have a basement drain near where they were working. The excavator was used to hoist out the two chunks of concrete that were removed to make the doorway.
When the men arrived with the precast root cellar, the first thing they did was measure the dimensions of the hole in the ground. They then shook their heads and said that it wasn't going to fit. Oh my, that was not good news.
Apparently, unbeknownst to me, they had made it 8' by 13' by mistake, instead of 8' by 12' which was specified in the drawings. The bedrock was jutting out into the area where it would need to be placed.
The men knew that the size was wrong when they loaded it onto the truck, but hadn't called me to let me know. Oops!
Determined as I am, I said I thought we could make it work anyway. So they got out their drills and various other tools and set about carving away at the bedrock.
While they were doing this, I got up on the truck to check out my new root cellar. I discovered that one side had a large crack in it, which had been patched! I'm guessing that it cracked when it was being put on the truck.
I called and spoke with the owner of the company and we agreed that we'd work out an adjustment to the price, which we later did.
When it was being swung around so it could be placed in the hole, I think it began to crack some more, in one of the corners. The fourth side (the side without the tar) was partially open, so this very heavy structure wasn't stable enough to hold together.
After many attempts, the root cellar has been lowered into place. Whew!
The side that's close to the house is sitting on the same footings as the house foundation. And that side was also bolted to the wall of the house foundation.
You can see a new crack in the corner in the foreground in the photo.
We had planned to put a type of rubber gasket between the root cellar wall and the house foundation, but due to the trouble in hoisting the cellar into place, this turned out not to be possible. The gasket would have helped keep water from seeping in.
Tar was put along the top edge of the concrete structure before the top was put on, to keep moisture from coming in between that edge and the concrete top.
The top was then hoisted into place. It was getting dark by that time, so the photos didn't come out well enough to show that part of the process.
The next step was to cover the root cellar with heavy-duty polyethylene (plastic) to give more protection against water infiltration. Then crushed stone was poured around the outside to improve drainage and the top was covered with soil.
After these photos were taken, an elbow was attached to the bottom of the cold air intake pipe to direct the air toward the middle of the root cellar. Both pipes were covered with a "door" that can be opened or closed as needed, in order to maintain the desired temperature.
I had an insulated metal door installed between the basement and the root cellar. This was especially important in my situation, since my woodstove is in the basement and I wanted to keep the warm basement air from affecting the temperature in the root cellar.
Then a laundry sink was added outside the root cellar door, so I'd have a place to wash off the veggies before bringing them upstairs.
This sink has come in very handy! It was an extra expense, but I'm very glad I did it.
Finally, I added the metal shelving which is solidly attached to the walls. This shelving allows for good circulation behind and around the baskets, bins, or other storage containers.
On the left, you can see my thermometer and humidity gauges. There are two of them because I wanted compare the readings to test their accuracy.
I still need to add at least one light and maybe an outlet for plugging in a fan to facilitate the flow of air on cool spring and fall nights.
Lessons I Learned: What I Would Have Done Differently
- The main mistake that I made was to have it precast and delivered rather than having it cast in place. If there had been no gap in the fourth side, there would have been less likelihood of cracking since the structure would have been more stable. In hindsight, a structure such as this is less than ideal for being moved with a hoist. A better choice would have been to have the footings and the walls for the root cellar poured right in place, like would be done for a house foundation. Also, I think the cost would have been less if I'd had it cast in place.
- Another mistake was not having that gasket put between the root cellar wall and the basement wall. The tar that was applied above that area didn't seal it completely, either. As a result, when it rained, water leaked in that area, causing the door frame to swell and the door to stick. (The problem had to be solved from the inside, since the outside was now covered with the raised beds. I did this by applying Water Plug. And the door was planed to make it slightly smaller so it would no longer stick.)
It's important to check your local and state building codes to make sure that you're not in violation. In my state, the root cellar is considered part of the house and thus has to be located a certain distance from the well. Also, make sure you don't need a building permit.
More Information and Articles
Building a Root Cellar: Here's a great step-by-step article by someone who had one cast in place, like a regular foundation would be. This is an even more elaborate project than mine, but very interesting.
Outdoor Root Cellars: Very helpful information about cold storage of vegetables when you don't have an underground root cellar. Includes descriptions of a trench silo, a "hole-in-the-ground pit", a garbage can cellar, and a root clamp. From Mother Earth News.
Creating a Root Cellar: This article by Eliot Coleman provides details about location, drainage, insulation, and humidity. Includes illustrations. Describes some easy techniques such as using metal garbage cans buried in the ground.
Root Cellaring: Excellent article by Nancy and Mike Bubel about building and using root cellars.
Build a Root Cellar: Another good article from Mother Earth News. This one is about converting a septic tank.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.