Root Cellars
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Q: I'm helping a gal with a project with a few strawbale outbuildings and she is interested in doing a root cellar either separate or possibly attached to her future home. Originally, the separate root cellar concept would have been constructed of cinder block and then bermed with earth. But since she is hitting bedrock at 3' she would have to berm to at least 5' with rigid insulation on top and possibly a portion of the sides to keep the structure to a more modest profile as her land is fairly flat. I was wondering what direction would you go, given the constraints of the bedrock being at 3'. My inclination would be to incorporate it into the future structure in the basement where it would have the greatest contact with the earth, and insulate the common wall to the home.

A: One question is does she want a true root cellar, or just a cool pantry? Root cellars are typically kept much more humid to preserve certain root crops, whereas a cool pantry is useful for storing a wider range of food supplies and other things as well. The walls and floor of a root cellar are often left without a moisture barrier to the surrounding soil to help maintain the humidity.

Your thinking about locating the cool room in the basement of the eventual house seems sound to me. That way it would probably be more convenient to actually use, and would have maximum insulation from warm weather. I would suggest that it should be located on the north side of the house, and as completely bermed with soil as possible. The walls and ceiling that are common with the rest of the house should be well insulated, and the other walls don't really need to be insulated since you want the temperature of the cool earth to prevail. It is usually good to also provide some ventilation, with a low inlet vent and a high outlet. Closure for these vents can be provided for warm weather if necessary.

Q: I have a finished basement in my home and connecting to my basement I have a cellar or storm shelter under my front porch; 8 foot X 28 foot 8 foot tall 9 inch concrete walls, 5 inch concrete top and concrete floor. My question: Would this serve as a good root cellar in the winter and also as a good cheese cave? I might have to insulate some, this room also have a steel 3.5 insulated steel door. This room is completely concrete and about 1.5 feet is above ground from the top of the front porch to the ground level. I would greatly appreciate your reply.

A: The suitability of using this space for a root cellar or cheese cave depends on several factors. A traditional root cellar is designed to keep certain kinds of produce, and often needs to be fairly humid. I am not familiar with the needs for storing cheese, so I can't address this. Have you monitored the temperatures and humidity in the storm shelter over the course of a year? This space might work well for your needs, especially if it doesn't freeze in there during the winter. This an excellent article about root cellars that might help you determine if the space would work for you: tribwatch.com .

Q: I am planning to build a root cellar/cheese aging cave this spring. I was planning on dry stacking cement block and surface bonding it for the root cellar. Most design I have seen show a poured slab for a ceiling. My plan is to build a small strawbale cottage above the cellar. I would like to have a good layer of insulation for the cellar. I have seen reference to papercrete floors but I have not seen references to floors over a cellar. Would this work? How would I have to support it (tentative dimensions are somewhere between 12ft.X 12ft. to 16ft.X 16ft.)?

A: I doubt that papercrete would be a good choice for this application. Yes it is insulating, but it also absorbs moisture quite readily, and since a root cellar typically has a fairly humid environment, this could lead to problems (mold, etc.). Also papercrete is not nearly as strong as cement, so it may not support the floor. I would say that the deck over the root cellar might best be framed with manufactured I-beam joists and filled with standard fiberglass insulation. I know that this is not a particularly green solution, but given these circumstances it might be the best choice.

Q: We recently built a new house and included a "root" cellar in our basement using plans we got off the internet. The room is 5'x8' with 2 poured concrete walls and a concrete floor. The other two walls & ceiling are drywall but they are well insulated. I have a 3" vent in the floor and one in the ceiling that both come out under our front porch. The problem is we can never get the temperature below 67degrees or the humidity up enough so that we can store potatoes and other vegetables. I really need help in figuring out where we went wrong--I have a large garden and winter is coming soon.

A: With the information you provided it is hard to pinpoint what your problem might be. Root cellars work best if they are basically coupled with the earth all around (and even above them), and kept completely away from where the sun shines.  If the concrete walls are exposed to the sun, or even the air, then they could be conducting heat into the space. Also, during the summer when it is warm, the air intake may be introducing air that is too warm; if this is so you might block off the vents, especially during the day when it is warm. If the space was just completed, and all of the concrete is still warm from exposure and curing, then it will take quite awhile to cool down. Also, in an ideal root cellar, the space would be too moist for a sheetrock wall to last very long. If it weren't for the sheetrock, I would recommend that you periodically dampen the concrete to increase the humidity and introduce some evaporative cooling. Hopefully the space will cool over time with the changing seasons.

C: I should have told you that the 2 concrete walls in our basement "root" cellar are surrounded by earth (it is in a corner of the basement) and the house was built 2 years ago. So my last question--I promise--could it be possible that it is our ventilation system that is not working properly? Both ceiling & floor vent pipes come out underneath an enclosed porch and I'm wondering if they need to be "out in the open". By the way--we live in Iowa so the weather typically should work in our favor. Thanks for your help! I really love gardening but it breaks my heart to see my potatoes, squash etc... go to waste.

R: Theoretically, the temperature of the earth down about five feet below the surface is fairly constant all year round. In Iowa I would guess that that temperature would be around 55 degrees perhaps. So a room in the ground at that level should stay about that temperature. Obviously, your root cellar is being heated by other factors, and certainly the air being vented into the room is a prime suspect. If the daytime air temperatures are in the 90's, then this air will be trying to warm the space. You have a couple of choices: either close off the air vents until the outside air temperatures drop below 55 degrees...possibily even opening them only at night at some point...or you can dig a very long trench about 5' deep and maybe 100' long to run your inlet air vent in, so that the earth can cool the incoming air before it enters the root cellar.

I am guessing that your basement foundation was insulated on the outside before it was backfilled (which is a responsible thing to do, normally); this tends to isolate the concrete from the surrounding soil, so that it can reach a warmer temperature and stay there. Also, since the walls of the basement are continuous from inside to outside the root cellar, the temperature from outside the room will always be bleeding into the room. Obviously isolating one corner of a basement with insulated walls is not sufficient to create a true root cellar. At some point you, while less convenient, you might consider making a real root cellar away from your house, in a shady spot, where it can be dug way down into the earth, with just a gravel floor, and where you can provide the moisture that it deserves to keep the humidity up for the root crops. Then you can devote your basement room to the storage of dry goods.

Q: I live on a small farm in Springbrook, Ontario on what can only be described as a rock farm. We have anywhere between 2"-1.5' of soil over bedrock. We have broken backhoe teeth, rock drills, jackhammers etc. trying to get through the rock, with absolutely no success. We grow most of our own produce and are in serious need of more cold storage for our root crops (lots and lots of potatoes etc.) All of the buildings on the property were built from material found on the property, and we would like to do the same for a root cellar as much as possible. We have access to cedar, as well as other softwoods and maple, ash and oak. We also use the native stone where possible. I was wondering if you could direct me to resources for building an above ground root cellar using what we have as the major materials?

A: I can envision a root cellar fashioned mainly from your native stone, built up above ground and then bermed with lots of soil (I guess you might have to have this trucked in). This in essence would give you most of the advantages of digging into the ground for your cellar. The best would be cover the roof with soil as well, by either making a dome or vault with the stones, or using large timbers to frame a roof that then gets a sheet of plastic put over it before being covered with soil. Cedar would be the best wood to use in any below-grade application, since it naturally resists rot.

Q: I have recently returned from a trip to Meru, Kenya. I am working with a group of women that are looking at ways to keep their fruits and vegetables for a longer period of time. This area of Kenya doesn't get terribly hot, but stays a temperate temp. of 50 degrees at night and 70-80 degrees, at most during the day. It is about 6,000 feet up Mt. Kenya. I understand that it wouldn't' be like a root cellar where the temp is quite cool, but do you think it would keep things a week or so longer than just their home? They do have an area that is hilly and they could dig a cellar into the hill. Would you give me some feed back and help me to decide whether this is feasible or not.

A: In a temperate climate such as this, you might expect the temperatures about 4 or 5 feet under the ground to be fairly constant, perhaps about 60 degrees F. While this is obviously not refrigerator temperature, it is better than what the air temperature during the day would be, by 10 to 20 degrees...it would help preserve produce somewhat. If there is a source of water that could be introduced into the cellar, the evaporative cooling effect could also reduce temperatures noticeably. Some produce stores well in a humid environment, while other doesn't...so this could also be a factor for consideration.

Vegetables that like to be cold and very moist (32-40 degrees F., 90-95% humidity) include: carrots, beets, celery, Chinese cabbage, kohlrabi, Brussels sprouts, rutabagas, turnips, collards, broccoli and Jerusalem artichokes. Produce that likes to be kept cold and fairly moist (32-40 degrees F., 80-90% humidity) include: potatoes, cabbage, cauliflower, apples, grapes, oranges, pears and grapefruit. Produce that likes to be kept cool and fairly moist (40-45 degrees F., 85-90% humidity) include: cucumbers, sweet peppers, cantaloupe, watermelon, eggplant and ripe tomatoes. Vegetables that prefer cool and dry conditions (35-40 degrees F., 60-70% humidity) include garlic and onions. Produce that likes to be stored in fairly warm, dry conditions (50-60 degrees F., 60-70% humidity) include: dry hot peppers, pumpkins, winter squash, sweet potatoes and green tomatoes.

Q: How or what do you use in a root cellar to keep the mice/rats away? I put my food in plastic totes and it is wet in the inside...suggestions?

A: The best way to keep rodents from getting to your food in the root cellar is to make the cellar mouse-proof. If this is not possible then I suppose that the food must be put in some sort of containers that they can't get into. There are different climatic conditions required for various kinds of foodstuffs, so it is hard to generalize any further than this.

How about something for potatoes?

Well, potatoes need to breathe and have a cool, somewhat damp environment. I would consider placing them in wire cage of some sort that would keep the mice from getting to them.

Q: We have a hole 4m by 3m dug into the side of the hill - facing south - our cold side here in NZ. It is 1.6m deep at the most. I want to build a root cellar using concrete block - 200mm wide and high. The part of the building that is not underground I intend will be covered with earth. I would like to include a curved ceiling as I understand it prevents drips forming that will damage the food. I can find plans for wooden structures but not concrete - can you tell me where I can get such plans?

A:   A quick Google search revealed a couple of articles that might be of interest, both using concrete. The first one actually uses a pre-cast septic tank for the cellar. To curve the ceiling, you could construct a barrel vault using the blocks if you were willing to make a form to hold it up during construction and wait to release it until the sides are backfilled. http://www.motherearthnews.com/Organic-Gardening/1983-07-01/A-Flatlanders-Root-Cellar.aspx http://www.agf.gov.bc.ca/resmgmt/publist/Leaflets/FruitVeg/331-50.pdf

Q: I need advice on how to build a root cellar above ground. I have red clay dirt that is too hard to dig into. Any advice would be grateful.

A: Root cellars generally do much better under ground. While clay is quite hard to dig into when dry, it will usually give way when damp, so you might try soaking the area before digging to see if that helps. Otherwise, it is possible to make a mounded-up, or bermed, root cellar by building a supporting structure of suitable materials at ground level and then dumping soil over it.

Q: I am looking to build a bank root cellar out of native Pennsylvania stone complete with a barrel vault ceiling. Excavation is not an issue, but do I build a wood form for the vaulted ceiling? How was it done 150 years ago?

A: I can't imagine a way of constructing a stone barrel vault without some formwork; domes are possible, but not vaults. However, you don't need to construct a form for the entire length of the vault if you  don't want to, since it is possible to make a short vault form (even just a yard wide)that is then released and moved in sections as the work proceeds.

Q: I am very interested in building a root cellar, however in coastal South Carolina the water table is very high, so digging anything is out of the question. My house is on a 5' high crawl space with cinder block walls on all four sides and dirt floor. It stays cool under the house even in the heat of the summer and the few below freezing winter days it stays about 50 degrees year round and humid. My question, do you think it would be possible to build a root cellar under my house and if so leave the floor dirt or pour concrete. Any suggestions would be appreciated as I have a large garden and want to be a self sufficient as possible.

A: A true root cellar is typically rather humid, and 50 degrees F. is a little warmer than the ideal 40 degrees would be, but then it is better than the ambient temperature.  Under your house could be a convenient place to carve out the space for this. I would do it on the north side, away from the sun, and if you isolated the space with insulated partition walls you might be able to lower the average temperature somewhat. Root cellars often just have dirt or gravel as the flooring, as this helps with the humidity. You should arrange some sort of natural ventilation, with a low inlet air vent and a higher outlet vent.

Just because you have a high water table would not rule out digging into the ground somewhat and berming up around an exterior root cellar. The humidity from the ground is actually a plus (for some but not all foods, see my article about pantries. You can actually create a cooler space through evaporative cooling if you have moisture, so I would seriously consider this as well.