How to Make a Root Cellar
Even if you live in a newer house, you can still have a root cellar. The following are simple plans for transforming a corner of your basement into a root cellar, with a minimum of know-how and readily available materials.
Choose a damp spot. Most crops keep best in relatively high humidity. So build your root cellar in the dampest area of your basement (typically the sump pump is in the dampest corner).
Locate it next to an exterior wall. You want, if possible, to build on a wall that’s below grade (underground), because you want the greatest contact with outside soil temperature you can get. If you need to use a wall that’s above grade, be sure it doesn’t get too much sun. (Use north or shaded walls.)
Allow for ventilation
Without ventilation, your stored produce will spoil. To create good ventilation, you need to get two pipes through that outside wall—one at the highest point of the room. Both pipes should be about 3 inches in diameter. Try to pick a site that allows for this easily, such as one that includes a casement window or the like.
Your vents can be made of just about any pipe or ducting. Plastic (PVC)—3 inch—is durable and easy to work with, and the valves you'll need fit right into it. Cut a length of the plastic pipe to reach through the wall. Cut the end straight. Slide a closed blast gate (valve) onto the pipe until it fits snugly against the end of the pipe just tight enough to impart a slight resistance. Use 3 or 4 screws to secure the valve to the pipe.
Now cut pieces of pipe for the other vent. This one can go through the wall just about anywhere; just add an elbow and a length of pipe running down the inside so that it ends up about a foot from the floor. Add another blast gate in that pipe.
These two vents create a siphon. Cool air is more dense than warm air, and will collect in low spots. Anytime the air outside your root cellar is cooler than the air inside, the siphon will allow warm air to be drawn out and cool air to flow in. As outside temperatures fluctuate, you'll get almost continuous air change while keeping the temperature as low as possible.
Which brings us to the reason for the valves. If the temperature outside goes below freezing, you should close one of the valves to stop the siphon. You'll get some venting while keeping things from freezing. If the outside temperature goes way below freezing, you'll need to close both valves (at least partially).
Seal the wall around the pipes with aerosol insulating foam. This will fill in any gaps and cracks and, once it sets, does a good job of holding your pipes in place, too.
Build the walls
You could build the walls out of just about anything, but, due to the moist conditions, you should splurge on a handful of 2-by-4s made of cedar or other rot-resistant wood for framing, and some moisture-resistant wall board (“green board” sold for use in shower stalls).
Nail a 2-by-4 to the ceiling, fasten another to the concrete floor with a bead of construction adhesive (the kind in caulking gun tubes), and cut the studs to fit between them.
Cover the walls
Put your gypsum board on the inside surfaces first. Once the inside panels are glued and screwed in place, stuff the cavities with fiberglass insulation and cover the outsides. With all of the coverings in place, get out the aerosol foam again and shoot it into all of the cracks—especially between your new wall and the (likely) ragged edges of the old walls.
A root cellar does not need to be airtight, but the tighter it is, the more control you’ll have over the air quality and temperature. Plug as many gaps as you can.
Add the shelves
Bear in mind that lower shelves will be cooler and wetter, while higher shelves will be warmer and dryer. Arrange and space your shelves to suit the items that will likely be stored on them.
Hang a door
You can use a ready-made door if you want. Or you can make it simply from quarter-inch plywood and hang it directly on the studs. One customizing touch worth considering is to make the door in two pieces. This way you can open the top half and grab a couple of carrots without letting out the coldest, dampest air at the bottom of the root cellar.
Fasten a rod to the handle of each blast gate and run it through the wall into the basement. This way you can open and close the valves without opening the door and spilling the cold air. It also will allow you to see whether the valves are open or closed without opening the door.