Built-in Root Cellar
Not every property has the luxury of a north facing hill with well-drained, diggable soil that is free from large tree roots. It is for that reason that we explore the possibilities of constructing a root cellar in your existing basement.
As with the outdoor root cellar, the process begins with site selection. For construction simplicity, place the root cellar in a corner- this makes two of the walls up against the exterior which will be cooled by the earth. For those of us in the northern hemisphere, a northeast corner is best as the soil outside of your exterior walls will be significantly cooler than that which receives direct sunlight. A corner site is also less obtrusive to whatever else you may be using your basement for. (insert your own Hannibal Lecter reference here!)
If at all possible, place the root cellar where there is already an existing basement window. In fact, this may be even more important to you than placing it in a corner as a key component of the root cellar is external ventilation of warm air, vegetable odor and ethylene gas so unless you are comfortable with knocking a hole in your foundation, choose a location with an existing window.
As always, check local building codes and secure any required permits before embarking your project.
Once you have selected your site, consider how much space your root cellar will need. 2 x 4 lumber typically comes in 8 foot sections and for simplicity’s sake this is probably the best length to make your walls. So in effect, you will be building two 8 foot walls to complement the existing exterior walls in your basement for a 64 square foot root cellar.
If you have a dirt floor in your basement so much the better. Excavate below grade to a depth of 8 inches and fill this with gravel. Compact the gravel. This will allow the all-important moisture from the ground to migrate to your root cellar while providing a dry and firm surface for you to move around on.
For those of us that do not have a dirt floor you can create “cold sumps”. For an 8’ x 8’ root cellar this would entail breaking 4 holes, 6 to 8 inches in diameter evenly spaced in your existing floor. Using a post hole digger, excavate to a depth of at least 4 feet. Shore up the holes with 6” diameter high density polyethylene pipe that you have perforated with ½ inch holes. You can get 10 foot sections for about $14 at home supply stores. Fill the pipes with gravel and you should now have access to not only cool air from the soil but moisture as well.
If breaking holes into your basement floor is not on your playlist, you can introduce moisture by periodically placing wet burlap on the floor of your root cellar. In fact even with a dirt floor or cold sumps you may want to do this depending on your individual situation as a good root cellar requires 90-95% humidity. You can measure humidity with a hygrometer, available at most home supply stores for around $10. Get the digital kind that includes a thermometer and place it on one of your shelves.
Frame the root cellar as you would any other non-load bearing wall, again, following code. Install an insulated door. For the bottom wall plate, use composite decking material. It’s a little more expensive than whitewood or ground contact pressure treated lumber wood but given the constant high humidity it is essential. Do NOT insulate with fiberglass insulation. It will eventually harbor colonies of mold. Instead use foam sheets. Its easier to work with anyway and you won’t have any stray fibers floating around.
Remember we wanted to situate the root cellar on a window? That is because it is important to keep air moving in the root cellar. Using plywood, modify the space where the window once was. Mount a 3 to 4 inch wide ventilation fan blowing the air OUT of the root cellar on the plywood. On the floor of the root cellar, as far from the ventilation fan as possible, mount a 3-4 inch diameter intake pipe. I used PVC but you can make do with whatever you have on hand, just be sure to screen it so that rodents or other pests cannot use it to access your vegetables.
Use shelving to keep everything off of the floor (to promote air circulation) and maximize storage space. Keep the shelves at least 2 inches off of the walls, again for air circulation.
You may wish to add a light as well but remember to keep the root cellar dark when you are not in it.
But what if you don’t have a basement? Well, that will be our next article.
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