Root Cellars

Kelly Hart is your host at greenhomebuilding.com. He and Rosana created a large pantry (about 150 Sqare feet) in their earthbag house. Kelly has produced a video, titled Building with Bags: How We Made Our Experimental Earthbag/Papercrete House, which chronicles the adventure of building this house, and shows some of the making of this pantry. Kelly is available to answer questions about what he has done, or consult about other pantry or root cellar projects.

Questions and Answers

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: I'm converting an old underground storage building into a root cellar. The structure is very sound, built of cement block (made about 1950), but has a few cracks in the mortar. I want to seal the cracks and coat the interior with something that will seal it. I was advised to use a product called Sureseal, something like a mastic with fiberglass. My question is for a recommendation on what product would be best for this, and would not out-gas anything since we'll be using it for food storage.

A: A true root cellar for storing root crops and some fruits should actually be fairly humid to keep the produce well. Other kinds of foods do require a drier environment. So it depends on what you want to store in there whether it would be a good idea to seal the interior. If you need it to be as dry as possible, then something like the Sureseal product might work. From your description it sounds like what is called a surface-bonding cement that is very strong and can actually be used to make walls with cement blocks that have no mortar at all. As for out-gassing on these products, you would have to read the labels or talk to the manufacturer to find out specifically.

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

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.

Q: I'm looking at building two types of storage for food. One may be a small root cellar and the other a larger cool storage outside pantry. First of all, how does one make the root cellar humid? We live in Utah, so it can get pretty cold. However we don't usually have a lot of snow. Where I live, the water table is 4 to 6 feet down, so I'm reluctant to dig down too deep into the earth.

A: Usually a humid root cellar is kept damp naturally through contact with the soil, or even a stream flowing through the space. Contact with the water table may be the best way to keep your root cellar damp. It depends on what you want to store whether it is appropriate to have high humidity or not.

Q: When we moved to our old farm, the root cellar was dry and free of mold. We decided to plant all kinds of bushes and plants around it and over the years, the root cellar has become wet and moldy. Did we cause this by introducing plants that sent their roots down and drew the water with them? How can we get our DRY cellar back?

A: Hmmm, obviously something has changed, and it could be your plantings, especially if you are watering them where before the area was not watered. Or it might just be some natural change in the migratory nature of your water table...hard to say. Plant roots will go where the water exists, not usually the reverse of this, although roots can eventually open up cracks that will allow water to enter a space. If the area above the cellar is being watered, you might stop this, or diminish it for awhile to see if this helps, depending on how dear your plantings are to you. Another thing to do is make sure that there is adequate ventilation in the cellar; there needs to be at least two vents: one as low as possible and one as high as possible. A true root cellar should actually be rather humid by definition, depending on what you want to store there. Keeping a storage room below ground absolutely dry is not easy. As a last resort you may need to uncover the entire room and seal it with a moisture barrier if you want it really dry.

Q: I reluctantly moved to a new home in a subdivision with a high water table and a basement no more than 3' below grade. In the north corner there are no windows, plus bordered by the attached unheated garage. I'm trying to figure out how to turn this 1/4 of the basement into a root cellar (outside wall) and cold storage. Any tips on building a basement root cellar in a house in suburbia? Minnesota -- looking for storage from October through April, temps from -30 winter to +40 fall/spring.

A: Basically it sounds like much of your situation is ideal for conversion to a root cellar. The fact that the best basement space is on the north side is good and the attached garage on that side should moderate the temperatures in that area somewhat. You may want to separate the storage area from the rest of the basement with insulated walls, especially if there is a temperature differential down there. The tricky part of establishing a true root cellar in a basement is introducing enough humidity, without adversely affecting other areas of the house. With a high water table it may be that there is already enough humidity there. You might check this out with humidity gauge, comparing the readings to the ideal range for whatever produce you want to store there. If you need to increase the humidity, you might be able to do this with open tubs of water or a humidifier. All root cellars and cool storage facilities require good ventilation, with an inlet vent (at least 4" diameter) as low as possible and an exit vent (to the outside) up high. The inlet vent would ideally provide outside air rather than the air from inside your garage. If the inlet vent pipe is buried for several yards, so much the better.

Q: I have been thinking about making a wine cellar/root cellar using a geodesic dome made from PVC pipe and then using adobe bricks to go around it and back fill around it. Now I think I like putting earth bags as a quicker solution. I am going to place it in such a place that there might be a lot of run off in the winter. I guess a French drain around it would be a good option. I also think I might use an old swimming pool liner to cover it with rather than netting?

A: I think you would be wise to use earthbags rather than adobe bricks for such a structure, since they can withstand moisture much better. A swimming pool liner should waterproof this quite well, and a French drain should keep it from getting too damp inside. You might look at this page about another approach to building a root cellar using earthbags: http://earthbagbuilding.com/projects/rootcellar.htm

Q: My husband and I would like to convert our pool to a root cellar with a garden on top. Have you ever heard of this? Do you know what types of materials we should use?

A: No, I have not heard of anyone doing this, but it seems entirely feasible to me. The main structural aspect is making a roof that is substantial enough to hold the weight of a garden, so this might require some very heavy wood beams or steel girders. Sometime there is a concern with pools collapsing from the sides if the water is drained, so you might check with a pool specialist about this before proceeding.

Q: I am going into production mode for our small family farm (7 acres) and am looking into produce storage methods such as a root cellar. I will most likely be storing produce that like it cool and fairly moist (tomatoes/cucumbers/peppers). I live in southeast virginia where shipping connex containers are readily available and are much larger (8'x8'x20-40') and cheaper than the affordable concrete options I've seen (ie. damaged septic tanks). I have not decided on in-ground or berm construction, but would like to know if this has merit as a root cellar or if you see any concerns.

A: You could certainly bury one of these shipping containers safely, and it should provide a reasonable climate for your produce, provided there is adequate ventilation and humidity. My main concern would be whether it would hold up OK over time. I've been told that many of these containers are corrosion resistant, but even painted steel will eventually rust in a humid and aerobic environment. It could be covered with a plastic liner I suppose, and this might afford some protection.

Another possible concern are the floors, which are often made with toxic, preservative-laden wood planks. If this is the case, it might be best to tear up the wood flooring entirely and just use a gravel floor, which is often advised for root cellars to help introduce the needed humidity.

Q: I live in the Willamette Valley Oregon, and I am wondering if an underground root cellar will work in this climate? Some people have been telling me they think it is too wet here, but I'm hoping that a concrete structure with vents will stay dry enough. I also thought of bringing in dry sawdust periodically to reduce the humidity. Maybe there are some other tricks like that for regulating the humidity that you can share?

A: I doubt that the ambient humidity in that region would be a problem for a root cellar. It depends on what you are storing in the cellar what the ideal humidity would be; many root crops actually prefer a humid environment, and cellars are often specifically designed to trap more moisture, such as with exposed dirt or gravel floors. This article mentions some of the temperature/humidity preferences of various stored produce.

Q: I am having a cement block root cellar built measuring 7' inside height and 16' long and 12' wide with a rebarred solid cement roof and intermittently rebarred cement blocks every 3rd block. The roof will be 8" below the surface and I wanted to line it with plywood so I could put shelves attached to an easy material such as wood. Also I was going to put R9 4'x8' foam insulation sheets and then another plywood sheet probably 1/2". What do you suggest I attach the first 1/2" sheet of plywood with to the cement block wall and is my plan sound in your experience?

A: If you are planning to make a root cellar that is intended to be quite humid for specific root crops, you might rethink the idea of using wood in such an environment. Also, insulation is usually not necessary in a buried root cellar, as the cool earth will help keep things cool without freezing. If your intention is to store things that require a dryer climate, then what you outline is perhaps a good idea. I'm still not sure that the insulation will do much good, unless you have some source of heat inside. It might be that the roof of the cellar is more critical for adding insulation, since 8" of soil is not much protection from outside temperatures.

You could attach the plywood to the masonry wall either with screws and anchors embedded in the block wall or with "molly bolts" that you can push through to the cavity inside the blocks and the nuts are spring loaded so they open up inside and won't come back out.

It is for dry storage. Our winters average around 15-35F - gets down to 5-10F in Dec and Jan. Also regular rain in the area. Based on that, how much dirt over the roof should I have, given it will be an 8" cement roof? And could that depth be offset by R9 foam sheet type insulation? How many sheets thick? Please give me your experience with this as best you can, given the complexity of going much deeper.

If you know what the average winter frost depth is in your region, then that should give you an indication of how deep the dirt should be above your cellar. The fact that much of the space will be below that level will definitely help moderate temperatures in the room, but the average temperature in there will be higher if you get below your frost depth. If this is not practical, then adding insulation to the roof is another option, and the more of this there is the more stable will be the temperature...to a point. I would think that about R-18 would be a good compromise.

The average frost depth is 8" in this area. Worst scenario 12". If that is the case would I be OK with an 8" depth and an 9" thick cement roof?

Yes, I would say that in this case you don't really need the insulation. The cellar should remain at a constant temperature of about 50-55 degrees F. is my guess.

Will it remain that 50-55 F in the summer temps of 80-90F which also has high humidity for about 2 months of the summer? I know the builders are going to put black tar sealer type paint on the outside of the cement blocks. Is it a good idea to have 6mil plastic sheeting wrapped around the whole structure as an added water barrier or is it not needed?

Once you go below about 6' underground the temperature remains constant year round. There are many ways to seal concrete foundations, and someone with experience in your region probably has a good idea of what is appropriate. I would follow the manufacturer's recommendation for whatever product you choose.

Q: I have a new root cellar built on the back of a new house 12 by 16 block, layed and insulated with 2 in. on the outside and 1 in. inside; in the ceiling, 6 in. The exhaust goes in and out. The wall connected to house has no insulation. Dirt goes up tothe roof boards. Shingled roof. It stay at 60 degrees and freezes in winter. Any advice?

A: Hmmm. That's frustrating to build a root cellar and have it freeze after all of the work and expense! So if I get the picture right, you have a well-insulated (except on the wall next to the house) concrete block cellar adjacent to your house. You don't say which side of the house it is on. The north side is the best (at least in the northern hemisphere), to minimize heat from the sun.

I suspect that all that insulation (except in your roof) is working against the goal of keeping a constant cool temperature. Usually in a root/cool storage cellar you want direct earth contact with the walls to take advantage of the relatively constant cool temperature underground. Since the common wall with your house is uninsulated, it will be passing heat into the room from the house, helping to elevate the temperatures there, but not sufficiently to keep it from freezing in the winter.

I suggest that you do insulate the common wall, but remove as much of the insulation on the other walls as much as is practical. You might add the excess insulation to the ceiling if possible. The other thing you might do is experiment with closing the vents during the winter to keep that freezing air from entering and see if that helps.

Q: I am in the process of having our basement done for a new house. I read through your website and have done a lot of research on root cellars. I would like to put this in on the north side wall. My question is should I not pour the floor slab in the designated storage space for vegetables so this room can be exposed to the gravel which is on top of the earth, doing this for moisture and humidity? I was thinking a room size of 10 x 6 and have half that be with the open floor with not concrete and the other half have it with concrete. Do you think this would work?

A: I think that what you describe should work fine, although the space in general will be fairly uniform in humidity. Depending on your climate and geology and what you want to store there, you may need to introduce more humidity, but this can be done. Be sure to include a low inlet and high outlet air vent as well.

Q: I have a new root cellar built on the back of a new house, 12 by 16 block-layed and insulated with 2 in on outside and inside 1 in in ceiling. There is a 6 inch exhaust in and out. The wall connected to house has no insulation. Dirt is up to the roof boards. It stays at 60 degrees and freezes in winter...any advice?

A: Hmmm. That's frustrating to build a root cellar and have it freeze after all of the work and expense! So if I get the picture right, you have a well-insulated (except on the wall next to the house) concrete block cellar adjacent to your house. You don't say which side of the house it is on. The north side is the best (at least in the northern hemisphere), to minimize heat from the sun.

I suspect that all that insulation (except in your roof) is working against the goal of keeping a constant cool temperature. Usually in a root/cool storage cellar you want direct earth contact with the walls to take advantage of the relatively constant cool temperature underground. Since the common wall with your house is uninsulated, it will be passing heat into the room from the house, helping to elevate the temperatures there, but not sufficiently to keep it from freezing in the winter.

I suggest that you do insulate the common wall, but remove as much of the insulation on the other walls as much as is practical. You might add the excess insulation to the ceiling if possible. The other thing you might do is experiment with closing the vents during the winter to keep that freezing air from entering and see if that helps.

Q: I have cellar building fever; planning to excavate a 6 or 8 ft square hole in a large bank. The walls would be dirt, the floor gravel and cinder blocks for the front exposed wall. Being a large recycler and welder by trade I was planning on using galvanized metal floor deck for the roof due to availability. I'm concerned about zinc leaching down! Is there a cost efficient way to cover decking or an alternative cost efficient way to build a roof. I'm planning on covering the roof with approximately two ft. of dirt from the excavation. Really trying to stay away from concrete due to cost. Had planned on several layers of plastic to cover top of decking.

A: You don't say which direction the cellar will be facing, but no matter which way it faces, it would be a good idea to insulate the block wall to keep it from gaining too much heat or transferring too much cold. There are very few soils that will support a vertical wall without some sort of retainer, whether this is more cinder blocks, earthbags, or more of your galvanized metal that is sufficiently braced... especially with all the weight of that roof and soil above.

I wouldn't be too concerned about zinc leaching down; I have not heard of this happening with galvanized metal, at least in sufficient quantities to be concerned about. Be sure to install a low inlet vent and higher outlet air vent somewhere in the design.

Q: I am planning to build a small root cellar into the basement floor of my new house for the purpose of storing root vegetables during the long Maine winter. It will not be big, perhaps 3'X3'X3' with a simple wooden hatch opening up from the floor. The bottom of this compartment will be three feet below my basement floor at the daylight basement side...so it will only be about 5' below outside grade. Do you think this will be at an adequate depth? The walls of this storage compartment will be of concrete and the base will rest on well drained crushed rock and lined with bricks. Within the compartment will be a bin full of sand in which to store the root vegetables. I have not been able to find any postings online about this type of approach to a root cellar and thought you might be able to offer some insight. I question the ventilation portion of my idea as the compartment does not have direct outside airflow. So far the only air flow would be through cracks and seams on the wooden hatch on the top. Perhaps I should run a small pvc pipe to the outside air and seal with a strong screen to keep rodents out?

A: It seems to me that what you are planning should work quite well. According to my research, vegetables that like to be cold and very moist (32-40 degrees F., 90-95% humidity) include: carrots, beets, rutabagas, turnips, and Jerusalem artichokes. Potatoes like it only slightly less moist. So that is what to shoot for. My guess is that at that depth in your climate zone, the temperatures should be about right. Humidity is another issue, and may require a sprinkle of water on the sand on occasion.

It is a good idea to provide some ventilation, with a high outlet vent and a low inlet vent. These could be closed during really cold spells to assure that nothing freezes, but having some air movement keeps the space fresh and allows off-gassing of the produce to occur without harm.

Q: We are planning on building a root cellar on our 10 acre farm which is located in Austin County, Texas. Our land is flat pasture land and our top soil is sandy loam, but we're not sure how far down it goes. Because of our hot humid climate, I was intending to dig the hole for our cellar deeper than most folks usually do. Keep in mind that the typical southeast Texas summer includes at least 30 days of 100 plus degrees. The obvious problem with this is the weight of the soil on the roof of the cellar. If my cellar is 12' x 12' with a ceiling height of 8', how deep under the soil should my roof be before I risk collapse? And will the root cellar be effective under our normal Texas climate conditions?

A: I think it is wise to go as deep as is practical to access those cooler temperatures. How deep that might be really depends on the construction materials and engineering. Properly engineered such a structure could go to any depth, but beyond perhaps 6 - 8 feet below the surface there is likely little difference in temperatures. It might help to insulate the roof of the cellar, so that the upper temperatures don't affect the overall cellar that much. I suggest talking to a qualified structural engineer about what might work; there are too many variables for me to make specific suggestions.

Q: I want to bury a large chest freezer and use it as a root cellar. I am supposing that I need to get vent and air intake pipes installed, dig a hole not too far from my cabin, put some gravel in the bottom of the hole and put the freezer in so that I can open the top without earth falling in. I would have a container in the bottom for water to provide humidity. I would put hay bales over the top of the closed chest and a tarp over that. Now, my questions are: 1) Does this set up make sense? 2) Since I live in Nova Scotia, where we get quite a lot of rain, and my soil is heavy clay, do I need to drain the hole? And how do I do that? It seems like every hole I dig accumulates water, even on the highest points of my gently rolling land. 3) Do I need to protect the freezer from ground water or freezing with plastic and/or additional insulation?

A: This is an interest project that you might get to work for you. I think you should drain that hole, probably with some gravel below the freezer that has a French drain running off to where the water can exit to daylight or a drainage sump. Wrapping the freezer with plastic probably won't be very effective, but you might consider wrapping it with more layers of thick rigid insulation that is intended for below grade installations. You might even use some of this on top of the freezer before placing the bales of straw. Whether this will actually keep the interior of the freezer from freezing is the question, and you will probably know the answer with time. You might need to close the air vents in times of extreme cold.

Q: I put in a root cellar using an 18'x8' steel fuel tank. I put a vent at the bottom and one at the top using 4" pipe. The temperature has been staying at 38 degrees but the humidity is at 95% and everything out in the open, like potatoes are getting mold on them. What can I do to get the humidity lower or should I cover the potatoes with something?

A: Yes, 95% humidity is a bit high; they say that the optimum for potatoes is 80 - 90%. You might experiment with covering the potatoes, possibly even with sand. Where is the moisture coming from...the floor? Possibly a moisture barrier would help. And then there are dehumidifiers...

Q: I live in Montgomery Texas right outside of Houston. I have two projects going but am in fear it is all for nothing. I am attempting to build a root cellar and a cold storage room. I buy a lot of food in bulk and always have a very large garden; truthfully, I always want to be prepared in case of any situation. I have been told by everyone but my husband that I am wasting my time on a root cellar. Our water table is around 6 ft. I am so clueless on how to build a cold storage. Right now I have a room in our extra mobile home dedicated for our extra food but summer is coming so I need to do something quick.

A: I wrote a general article about root cellars and cool storage rooms that you can read. Root cellars are often best kept rather humid, so even with a high water table you can probably dig down far enough to take advantage of the cooler temperatures below ground. Houston is a rather warm place, and the soil temperature several feet down will be around 71 degrees F. there, which is still warmer than ideal (40 - 60). So without mechanical refrigeration, it is hard to reach ideal cool storage temperatures in your region.

Q: What is the best method for constructing a root cellar? I know it should be in a north facing hill, and that it should be uninsulated. I'm thinking of doing a roughly 10' x 14' dry stack concrete block structure, but I'm wondering about the roof. A 10' span is pretty big, and if I pile 3 or 4 feet of dirt on top of it, that's quite a load. Do you know of any good resources for calculating the strength of a poured concrete ceiling?

A: (Nabil Taha) I do not recommend dry stack blocks at all because you have relatively high earth pressure. Walls must be made from reinforced concrete or reinforced masonry. For the roof, an inch thick concrete with the proper reinforcement will do it. But, it has to be engineered.

Q: Wanting to build a root cellar and have an idea. If we were to dig a hole in the side of a hill and use a fiberglass shower stall turned upside down for the 3 side walls and ceiling, keep the dirt floor and frame up a wood door using Cedar Posts. We can use the drain as the upper vent and add on in the lower part of the cellar. We will backfill on top & sides. Do you think this will work?

A: This is an interesting idea that might work, but I couldn't guarantee it. Certainly a fiberglass shower stall will not rot under these circumstances. The big question is if it could withstand the weight and pressures of the earth. This would depend on the shape, thickness and size of the stall. It might be that it would have to be reinforced strategically to withstand these pressures.

Q: I purchased a home here in North Central Tennessee last August which has an 11 x 11 x 8 root cellar. At the time of purchase the root cellar was only a couple years old. It is however in disrepair. The entry door walkway walls had collapsed from force of earth and water. The main structure is sound....I think. I have rebuilt the entry walls to 7' in height and filled them with re-bar and concrete and put a 5" thick heavily re-bar supported roof. My idea was to create an anti room to regulate heat gains in the summer. The entry wall remains about 40% exposed to air and morning sun as it faces NNE. I am working on burying the exposed parts of the structure and perhaps putting more soil on the rest of the roof which is only 9" covered so far. Here are my questions:

I want to keep the soil as dry as possible. I bought some 6mm black poly. Will this work? Is one layer sufficient? I thought I would camber the soil at a certain depth then lay the poly down then, then a bit of gravel then a layer of landscaping fabric to prevent silt infiltration into the gravel then cover with soil then plant grass. Sound okay? Another question which ties into the first one is just how much soil should I cover the root cellar with? I spoke to the builder and he said you could park a dozer on top of it, but he also built the retaining walls......The ceiling is flat with two vent pipes in it, about 5" thick. No cracks visible. Not knowing the actual integrity or how much re-bar was used I am tempted to put a post in the middle of the room, but that will hinder some movement. I just do not know the strength of a concrete ceiling to know how deep to pile the soil upon it. Any thoughts? Also back to the first question...if the poly is a good idea, how deep below the surface should I lay it, or should I lay it directly on the top of the root cellar? Current Root cellar temps 72 humidity 85 Did great last winter except it had rapid temp changes due to excessive air exposure.

A: I think that you are fortunate to have a root cellar on your property, even with its problems, which you seem to be taking care of. I think that your idea of layering the soil, plastic, gravel, landscape fabric, soil and grass should work fine. As long as the soil beneath the first plastic layer is dry, it probably doesn't matter much whether it is up against the concrete or not. It is hard to know how much weight the existing roof can support; obviously placing a post in the middle should make it much more capable, and that is probably what I would do. The more soil you have up there, the better your root cellar will perform.

Q: Building a root cellar in my crawl space. I would like to use an area of 11 ft by 6.3 feet of space as a root cellar. The floor is concrete and the three walls are poured concrete. They face north east and west. The east wall faces the outside and is where I would like to install the ventilation systems. The south wall will need to be closed off from the rest of the basement and have an insulated door. The height is just over 4 ft. The ceiling will need to be insulated. Questions:

1. Can I use plastic pipes for ventilation or should I use galvanized. Is 3 inch sufficient or should I have a 4 inch diameter for each - intake and output . 2. What R factor of insulation should I used in the ceiling and wall and door. 3. What kind if insulation is best. 4. What should the inside wall and ceiling be constructed with.

A: Plastic pipe is perfect for vents; it will never corrode. I think that the larger 4" pipe would be preferable, although 3" would also suffice if there is some reason to use it.

The more insulation the better, but I would say about R-30 in the ceiling and R-20 in the walls and door would be adequate. Doors are often less than this, so do the best that you can. I would choose a foam product rather than fiberglass or other batt material, since this can withstand humidity better. If you are making a true root cellar, there may be high humidity.

You can use standard wood framing for the walls, but again because of the humidity you might want to provide a vapor barrier on the inside of the pantry. Concrete blocks, bricks, etc. would be even better.

Q: Have cement root cellar 30' long 11' wide and 8' high, made into 3 rooms so it can have different temperatures and humidity. It has 4" PVC intake and exit vents, with the intake low and the exit high on the walls. The cellar is covered with 3' of dirt. There doesn't seem to be any draw on the vents, so the temperature stays same day or night. Intake and exit pipes come out on top of a dirt mound. Pipes have a 90 where they come out of wall and then straight up, about 4 feet above ground level. I tried different heights to see if that would help and it didn't. Cut one 4" pipe and added a 6" diameter piece above that to see if would get more air flow. Didn't make a difference. Any suggestions on what would need to be done to get airflow in and cool it down at night?

A: I don't think that you can expect any significant difference in the temperature of your root cellar from having the space vented. The venting is mainly to introduce some fresh air and exhaust more stale air. To notice a difference in temperatures, you would need much larger vents (the size of windows or doors) that you control by opening when the outdoor temperature is significantly lower than inside the cellar, and then close them off when it gets warmer. The underground temperature, particularly with concrete walls, is going to remain fairly constant most of the year, regardless.

If you want a more positive draft on your existing vent system, you might try installing a taller exhaust stack and painting it black to make it warmer during the day. Either that, or installing a small exhaust fan to force the air out.

Q: I'm going to bury a chest freezer down to ground level with some gravel under it. I want to store Potato's and Tomatoes and Carrots. Do I need vents for moisture. We have white clay with a high water table here in Northern Utah. If so, how many, and how big, 2" 3" or 4"?

A: The ideal temperature that would accommodate those three veggies is about 40 degrees F., with a humidity of about 90 %. The temperature deep underground in that region is about 53 degrees F., but a chest buried at ground level would likely get colder than that in the winter. It will be tricky to hit this target over a period of time, that is for sure. The size of vents could influence what the temperature/humidity is. My best suggestion is to size the vents fairly large, and then be ready to reduce or close them off as needed. If you had a gauge for the data with a remote readout, that might make it easier to make adjustments.

Q: I would like to build a root cellar, circular in shape and roughly 20' in diameter, and was thinking of using a combination of vertical earthbag walls and a reciprocal timber-frame roof. Do I need to apply a render/plaster to the outside and inside of the walls when they are buried?

A: Earthbags are great for root cellars; in fact I'm building one now that way. It is not necessary to plaster the bags on either side, because there will be no sunlight to degrade the bags, and you want the moisture from the soil to help keep the humidity up inside the cellar. A circular, vertical walled structure seems like a good design for this, since that shape is inherently stabile with the horizontal pressure from the bermed soil outside. The reciprocal roof should work well, but you will need to insulate it well to keep the cool inside the cellar.

Q: I've given some thought to having the floor in this root cellar simply be deep gravel over a dirt floor, but that just seems like it would be rife with problems, especially trying to clean the place over time. I like the idea of a concrete slab with a central drain that can be hosed out as needed.

A: Traditional root cellars do have dirt or gravel floors to help with the humidity (depending on the location), but a concrete pad directly on the dirt should also keep the cool, but not the humidity so much.

Q: I live near Gimli, Manitoba, where it is not uncommon to experience temperatures in the -30C range for several weeks at a time. The coldest temperature we've had so far this winter was -39C, not including the wind chill factor. Our area also has a high water table - less than one meter below the surface. I would love to build a root cellar, but our water table makes it impossible to dig down far enough to do an underground root cellar. Typically, our frost line goes down 4-5 feet. I've been reading about earth bag root cellars, and have been wondering if building one above ground and then creating a berm might work. Do you have any insights or suggestions?

A: I think that you have the right idea for your area, to dig down as far as you can given your water table, and then build up from there and berm the surrounding walls (and even the roof) with more soil. A true root cellar usually requires some humidity, so building close to the water table can be useful.

Q: Could one build a root cellar out of earthbags? My family is trying to become more self-sufficient with gardening, canning and storing food.

A: Earthbags are great for root cellars and below grade pantries. There is no need for insulation (except on the roof if it is not also below ground). The earthbags that are not exposed to the sun can be left without plaster if you want.

Q: I have an existing root cellar in an old bungalow home in northeast Nebraska. The cellar ceiling is located outside of the house structure with entry from my basement. In an effort to keep it dry, I would like to pour concrete on top of the cellar building a patio on top of it. Is this safe? I worry about it caving in.

A: That sounds like a nice arrangement with the entry to the cellar from your basement. What you plan should work as long as the supporting structure of the roof can withstand the extra weight. The only way to know if it can is to have someone knowledgeable take a look at it. I suggest contacting someone local who is qualified to make this judgment. There are some directories of green professionals listed partway down the home page of this website that might help you with this.

Q: I'm interested in building an underground root cellar using earth bags. It would be approx 10' x 12'. If I used logs as beams for floor joists. Could I build a small shed of the same dimension or a little bigger on top?

A: I think that you could do this. You might want to put some sort of insulation under the floor to isolate the root cellar from the upper room, and make sure that you adequately ventilate the cellar as well.

Q: In the absence of a north-facing hill, I am leaning toward digging a simple hole in the ground, building my walls with cinder block, leaving the ground as is, with gravel, and constructing a small shed on the footprint of the block walls. The shed can house many things so serves a double purpose, unlike a design which simply mounds up earth on top of the cellar ceiling. If I'm to run simple 2X8 joists over the top of the structure, would insulating the bottom of those (with say 4 inches of rigid) be sufficient to keep things cool?

A: Yes, I would think that that would be sufficient insulation.

What issues should I be thinking about in this scenario?

You might want to put a vapor barrier under the insulated floor/ceiling to keep moisture from migrating into the shed above.

Furthermore, where would the vents be routed? I'm guessing straight up through the roof (or sides) of the shed.

Yes, the outlet vent could go up the wall of the shed and through the roof. An inlet vent could be piped from the outside at ground level, then down to enter the root cellar near the floor.

Trap door opening to cellar would need to be super-insulated as well. Lastly, how to backfill this? Surrounding earth is mostly sand (well-drained); would I need to use pea-gravel to backfill all the way up to grade?

With well drained sand I think that the gravel is unnecessary.

What to coat the exterior walls with, if anything?

I would suggest coating the walls on the outside with something to keep the moisture out, since it could migrate upward into the floor structure.

If affordable, would solid concrete walls be a better way to go?

I think that your block wall system should suffice.

Q: I wanted to ask your advice about building a retaining wall, 2m high, of bags that will form a rectangular root cellar. I have seen some lovely root cellar ideas on the web with bags, however they all seem to use polyethelene as a barrier between the walls and the dirt. My understanding is that most winter veggies store better with good humidity so the root cellar benefits from being damp....With this in mind I was wondering whether earthbags could be used without a damp-proof membrane? Would they distort/shift with the extra humidity or be okay? Would it be sufficient to simply have some gravel drainage behind them from surface to frost with a pipe to take moisture away, as you would if using blocks?...Any thoughts whether vertical and pinned with internal rebar is as good as inclined into the bank a little?

A: A couple of years ago I made a pantry/root cellar with earthbags and I did line the side with plastic before I back filled it. I left the floor the natural soil and figured that that was sufficient to maintain the humidity. I also inclined the walls a bit into the bank so that I felt it was quite secure without further buttressing. With this I even dispensed with the usual rows of barbed wire between the courses of bags. Vertical pinning does help stabilize the walls, but I only did this on one side where it was adjacent to a garage with vehicles being parked nearby. Without a plastic barrier, the soil fill would fluctuate with dampness and likely contribute to humidity, but it might also expand and contract a bit if there is much clay in the soil and where it might freeze. Using gravel behind the wall would mitigate this to some extent perhaps, but if the purpose is to increase the humidity then the heaving might still be an issue.

Q: My house built in '40s has an existing root cellar with cinder block walls and red clay dirt floor which I have never used in last 30 years. I am getting the house ready to sell. I notice what looks like maybe black mold on cinder blocks. How should I get rid of the mold if in fact it is mold? Does the doorway need better sealing/insulation? Should walls be painted with Drylock?

A: Something black showing on the cinder blocks certainly does sound like mold, and if so this would indicate that there is present on the blocks both moisture and organic material. The best way to deal with the moisture and avoid more mold is to sufficiently ventilate the space. For that you need both an inlet and an outlet air vent. Simply sealing up the door tighter will not solve the problem. Probably opening up the door so the cellar can air out would be a good idea.

Then to get rid of the existing mold you might try combining 1 cup of bleach to no less than 1 gallon of water and use this in a spray bottle and apply evenly to mold stained areas. This should kill the mold, then any residue can be scraped off and the walls painted with several coats of lime mixed with water to keep mold from returning.

Q: I have a root cellar under my attached garage. Garage is unheated, and root cellar has dirt floor and is separate from basement under house. Root cellar (which I don't use) has batt insulation between garage floor and ceiling is made us of unfinished boards. Has excessive moisture, and boards are rotting, and insulation is falling out. Garage above, has cement floor, which in the past few years "sweats" we have rubber mat on it, and wherever mat contacts cement, is wet. how do we fix these issues?

A: This sounds like a classic case of an unventilated root cellar building up too much humidity with no place to go but into the surrounding materials. I suggest finding some way to introduce at least two fresh air vents into the cellar space, preferably with one low in the room and the other higher up as an exhaust vent to the outside.

Q: What are the different types and techniques of root cellars suitable for apple storage?

A: Apples like to be kept cold and fairly moist (32-40 degrees F., 80-90% humidity), so any root cellar that offers these conditions could be used. It depends on the local climate whether underground temperatures are in this range, and unfortunately there are few places that are this cool (Canada and Alaska, for instance).

Q: What are advantages and disadvantages of root cellars compared to electric refrigeration?

A: Root cellars do not rely on fossil fuel or electricity to maintain their temperature and humidity, but a disadvantage is mentioned above.

Q: Why are root cellars replaced with electric refrigeration in households and industries?
For example, financial reasons, convenience, longer storage, better taste, higher nutrients or perhaps other reasons?

A: Convenience or more control over the exact environment.

Q: How to create and maintain a low temperature and high humidity for apple storage?

A: The temperature and humidity in a root cellar depends on the climate of the location. Generally you want the cellar to be in direct contact with the underground soil to enhance the humidity.

Q: What are the best ways for ventilation and drainage in root cellars?

A: Ventilation is best maintained by having cool air entering the space from the floor level (piped in from out of doors) and then exiting up high in the space. Drainage is usually maintained with a layer of gravel on the floor, but this varies depending on how well the surrounding soil drains.

Q: Does storage of apples (or produce in general) enhance their taste and does it decrease nutrient content?

A: As far as I know the storage of apples (and other produce) can enhance their taste and does not generally decrease nutrient value, unless the time of storage is too extended.

Q: Are there zero or low-cost ways to build apple root cellars?

A: A good scrounger could probably create a root cellar for nothing.  A very simple storage system can be created with a buried garbage can.

Q: Are root cellars only suitable for home growers or also for large-scale farmers?

A: I think they are suitable for both.

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