To minimize our energy dependence, and since refrigerators (even the most energy efficient ones) are by their very nature energy suckers, we have to come up with better solutions for storing our food. Remember when... our grandmothers knew how to deal with this need. They simply built a storage facility into the earth, where the ambient natural temperature is usually around 55 degrees.
Fast forward to today. Many people have been living in areas where root cellars have been for a hundred years, and still using this free and natural means of protecting and preserving their crops. Thus, the design of root cellars has been finessed and a clear set of building criteria developed.
Root cellars are built into the earth, or surrounded with earth once they are built above the ground, on the north or east sides of a house. There are three styles of root cellar – hatch type, hillside type, and above-ground type. All three have slightly outward-battered walls to prevent collapse.
The hatch cellar type is the simplest, being a hole dug into the ground and walled in with mortared stone. It has a dirt floor. Wood beams and plywood sheets or wood decking are installed as a roof foundation, with a hatch in the ceiling and a ladder for access. A shed is then built over the entire cellar, with walls extending past the cellar on all sides by no more than 3 feet, so that moisture can still access the cellar.
The hillside cellar type is partially dug out of a hill, lined and walled with mortared stone to create a square room or rooms. Wood beams and plywood sheets or wood decking are installed for the roof foundation, an underlayment applied, and a traditional roof installed above. The access to this cellar is through a framed insulated door at the floor level. Sometimes this cellar is accessed through a few or several stairs, though we do not recommend this as it creates a falling danger in ice and snow. Especially for littles, who have a tendency to use the cellar as a secret fort.
The above-ground cellar type is framed traditionally, covered in building paper and felt, has a thick sod wall applied to the exterior, is lined inside with dry-stack or mortared rock, and accessed at floor level with a framed insulated door.
The best cellars in cool climate zones have four different rooms: The first - for fresh foods that must not freeze, with insulated walls and soil floor; the second - for fresh foods that may freeze, require high humidity, has soil floors and no wall insulation; the third - for fresh and dry good in sealed containers, with sealed concrete floors and walls and no insulation; and last - for fresh foods requiring some humidity, with a concrete floor. The next best cellars have two rooms – one with a concrete or stone floor and one without. The last and smallest cellars are a single room with humidity of 80-90% and dirt floors.
Shelves in all cellar types are self-supporting, not attached to the walls in any way, and are kept away from the walls by 3 inches to allow ventilation, deter the growth of molds, and deter access by pests. In the best circumstances they are placed on concrete blocks or stone bases to keep them off the floor as well.
A 6" minimum diameter exhaust pipe is installed in the ceiling to allow hot air to escape. If the roof is pitched, this pipe should be located in the crest of the pitch. If the cellar is installed in a basement or under a shed, run the pipe outside as quickly as possible as it is critical that it have access to fresh blowing breezes to function correctly. Include a 90 degree elbow bend at the end to face the pipe north or put a covering over it so that wind and other dropping things like leaves and bird poop don't plug the opening. A supply pipe should also be included near the floor and pup through the outside of the cellar walls to the fresh air, in the north side of the cellar and with it's 90 degree elbow inlet pointing north or northwest, but not attached, for adjusting during those periods when the prevailing wind direction changes, which will encourage the hot air to rise and be expelled through the exhaust pipe. Vents should be sealed around their pipe as they enter the structure with packed cloth, expanding foam or tight rubber gaskets. The vents themselves should be equipped with closing and opening valves, and it is convenient to make these valves operable from outside the root cellar. Closing vents in freezing weather and during summer heat spells will help keep the temperature inside the cellar more uniform. Stuff the first little bit of the vent's outside opening (2 inches, not enough to block flow) with steel wool, and cover with netting to keep pests out.
Humidity is key in successful cellar design, and in arid regions, you might need to bring water into the cellar to achieve the desired humidity. This can be done by pouring water directly into the cellar floor if you have a 6" gravel base installed, or you can just bring in a large pan full of water and put damp towels over your bushel baskets and allow the humidity to self-regulate. Also in arid regions which are ideal for sun-drying foods, you might have a larger area in your root cellar for dried foods in sealed containers. In humid environments, especially tropical ones, you might need to use a deeply planted hatch cellar that is highly insulated and with a minimal access point, in order to minimize the area exposed to the hot air and humidity.
The ceiling of the cellar should be sloped slightly to encourage dripping to occur where you want it, and should be as smooth as possible. Do not allow the structural elements to be exposed as this will quicken their deterioration. Plywood can easily be attached to the underside of your rafters, or a humidity-friendly wood decking installed.