Walls, Doorways, and Insulation
A root cellar that has been dug into a hillside is an underground structure with one exposed wall and an access door. The wall can be made from a variety of materials like wood, cement blocks, adobe, rammed earth, earth bags, and cob. These options are fully discussed in Chapter 4 “Build an Above Ground Root Cellar.”
To create an access door for your underground cellar, first mark off a thirty-two-inch wide space to serve as a rough opening for your doorway. Next, create the doorframe out of two by eight pieces of lumber. An economical option is to install a previously used door, often found at salvage yards, Habitat for Humanity restores, and garage sales.
Underground wall storage
Depending on what material you choose to make your access wall out of and the climate in your area, you may need to insulate your cellar. A wall made of wood will have to be insulated no matter what the climate, as wood alone will not keep the heat or the cold from coming through. Two feet of insulation material, placed between the interior and exterior wall, is ideal for a wood-framed wall. A wall built with hollow cement blocks is easily insulated by filling in the hollow area between blocks with some common material such as sawdust, loose straw, dry sand, or commercial insulation. A wall made of adobe, rammed earth, or cob needs no additional insulation as it is thick enough and the material used functions as a natural insulator. Your access door will also need to be insulated. One way is to cover the inside of the door with standard home insulation. To do this, cut two inch by four inch pieces of wood long enough to make a frame around the inside of the door. Nail the wood to the door then fill the two inch recess with insulation. Nail a piece of plywood to the outside of this frame to hold the insulation in place. A much easier way to provide insulation is to tack a heavy blanket or cloth to the inside of the door although this may not be effective enough if you live in a very cold climate.
Building an anteroom outside the entrance to your root cellar can offer several benefits. It can provide extra insulation for your produce, and can be used to store gardening tools, canning supplies, and empty canning jars.
If your underground root cellar has more than one room, you can help regulate temperature and humidity by having well-insulated walls and doorways. Hanging blankets on interior walls and over doorways is one way to regulate temperature throughout the cellar and provide an extra measure of insulation for your fruits and veggies.