Miscellaneous Questions about Earthshelted Buildings

Rob Roy is Director of the Earthwood Building School, which has specialized in cordwood masonry and earth-sheltered housing instruction since 1980. Rob and his wife, Jaki, have built four innovative cordwood homes for themselves since 1975, including the Earthwood home where they have lived since 1982. Earthwood is a 2400 SF two-story round, load-bearing cordwood home, earth-bermed and earth-roofed. Details of construction are in Rob's Earth-Sheltered Houses (New Society, 2006) and Cordwood Building: A Comprehensive Guide to the State of the Art (New Society, 2016) two of sixteen books he is written in the alternative building field. Rob and Jaki have taught cordwood masonry at Earthwood Building School in West Chazy, NY, all over North America, as well as in Chile, New Zealand, Australia and Hawaii. They have helped scores of owner-builders with their cordwood and earth-sheltered projects, including homes, saunas and outbuildings. Earthwood has produced a 3.25-hour DVD on cordwood construction, which, with his books, can be accessed through the Earthwood website, or on the Cordwood or Earth-Sheltered Housing  pages here. Rob is considered to be one of the leaders in the fields of cordwood construction and earth sheltering. He does individual consultations at a flat rate of $75/hour, but answers questions here without charge. See also Earthwood Facebook.

Questions and Answers

Q: If someone actually built into a mountain, would it stay cool in the summer or not? Even if it would, it seems like it would be very difficult to warm in the winter.

A: (Kelly) It works both ways, cooling and warming, because when you go underground there is a stable constant temperature that reflects the average of above ground temperatures annually. So in the summer, this tends to help keep it cooler inside, and in the winter it helps buffer the colder times.  Good passive solar design in this situation can provide comfortable quarters without the need for much other inputs.

Q: I have always enjoyed tropical settings. My dream is to own or have constructed a palace like home with open courtyards and architecture that seems to let nature become part of my home. My dream is to have a home built out of a small mountain with a connecting waterfront/waterfall or body of ocean. Your website didnt have information about architecture involving the use of mountains. Can you give me your brief recommendations, also what area in which my request would most likely be fessible ex: south america, madagascar, or any other tropical country.

A (Kelly): I have always been fascinated by the possibility of digging into mountains for habitation; there have been many societies that have done this traditionally. Here is a excerpt from an article I once wrote about the Ancestral Puebloan culture in the Southwestern U.S.:

There is a lot of speculation about why they decided to start building communities within the cliff faces. Some think it was for defensive purposes, although there is little evidence of violence to support this. My sense is that they moved to the cliffs for comfort. Some enterprising individual or family probably tried building a stone house on one of the many cliff ledges that faces south and soon realized that there were many advantages, which were pointed out to the others. Sealing off a cave or cliff alcove with rock walls effectively makes the room a part of the cliff itself. It’s like digging into the ground to take advantage of the cool in the summer and the warmth in the winter, but under the rock ledge they were also protected from the rain and snow and had much more thermal mass to buffer temperature extremes. Facing south, or southwest, as many of the cliff dwellings do, would allow the sun to enter the openings into the interior and also warm the stones, which would give off heat at night. During the summer, when the sun is high in the sky, much less sun would reach the buildings and they would remain cooler.

I got an indication of how well solid rock can modulate temperatures at another stop. On the outskirts of Moab, Utah is a 5,000 square foot dwelling blasted out of solid monolithic rock, called Hole-in-the-Rock. It is open for tours, so I checked it out and was informed that the temperature stays about 65 degrees F. all year round. Moab is at about 4,000 feet elevation, so it is a warmer climate than Mesa Verde, but even so the cliff dwellings must have been fairly comfortable most of the time.

There are many tropical locations that might be suitable, around the world.

Q: Hello, My wife, Rose, and I are planning to build a two-story house in a year-round tropical (hot-humid) climate near the ocean--Atlantic side of Costa Rica. What materials would you suggest? We are considering concrete and stucco. Where is a good place to get advice about what to do, or more importantly what not to do?

A: (Kelly) If I were to build in a hot-humid climate, I would seriously consider digging into the ground, where the temperature would be much cooler and more stable. A completely earth-sheltered home can be light and airy, if well-designed. Most underground building does use cement, but this is not the only way. A more ecological approach can utilize earthbags, filled with the local soil, sealed from moisture from the earth with plastic, and plastered on the inside for a pleasing wall surface. This approach could also be quite inexpensive.

Q: Thank you for the information. I may have given you the wrong information about "hot humid". It is always humid but the temperature year round is moderate, i.e., mid-day temperatures around 85 degrees and the night-time temperatures are in the high 60th. Sleeping is always comfortable with just a fan. Also since we are on beachfront we wish to build up, not down. Again, I would
appreciate any advise.

A: (Kelly) The most common strategy in such climates is to make the structure as "airy" as possible, so that the evening breezes can cool things down. The trouble with using dense, thermal mass materials, like concrete, is that they tend to stay warm once they become warm, so a house made of concrete may stay uncomfortably hot most of the time. I might investigate building with indigenous materials, such as bamboo, that doesn't tend to hold the heat.

Q: I would like a list of contractors that specialize in underground home construction if at all possible. I have been having a hard time locating contractors that specialize in that type of constuction. Any help that you can offer would be greatly appreciated.

A: (John MacMillian)I don't have a list of contractors that specialize in earth sheltered homes. For the most part, if you give them a complete design, any large, licensed, insured and bonded contractor should be able to build the home.

Q: I read, and if I got it right, that you recommend earth sheltering by digging underground in humid climate to deal with hot summer. I am sure what you are saying is right but I need to understand how it works. I thought it is the natural ventilation which is the most important for this climate and it could be difficult to achieve underground. please comment.

A: (Kelly) My comments are strickly theoretical, since I have not lived in a hot, humid climate nor experimented with my ideas in this area. I know that the vernacular way of dealing with these conditions is simply to provide plenty of natural ventilation, and this makes sense, as long as you are building above ground, since it is the only way to cool things down without air conditioning. I think that if the early inhabitants of a region had experimented with digging into the ground (in places where a high water table would not be a problem, or by berming up around the house), then they would have realized the advantages of doing this to help keep things cooler. The fact that a structure is mostly underground does not necessarily inhibit the use of natural ventilation; air vents can be arranged through windows and/or other vent pipes to provide as much air exchange as one wants. So, if you want to vent the cooler night air through a house, this is certainly possible. Dealing with the humidity would be pretty much the same in either case, without resorting to a de-humidifier.

Q: I have found a lot of general guides to evaluating the energy requirements for earth sheltered homes. Is there a way to predict heating, cooling requirements for such a home? I am sure that such an estimate would need to include ground temperatures, living space volumes and air movements, thermal gradients, weather, insulation and insolation, but it seems possible. Has this been done or do I need to start some modeling?

A: (Paul Shippee) Yes, there is a way; this has been done by me and others. Mmy book, THE LANGUAGE OF SOLAR ENERGY: Heat Loss & Solar Gain for Buildings that show how I did it; which, by the way, agrees well with extensive performance monitoring after the house was built. These results were compiled and published by the National Solar Data Network in the 1980's. ...and yes, the method includes all those aspects you mention in your question.

C: I have found amazingly generalized information such as fireplaces that are rated to heat 900 square feet.  Where, Florida or Alaska?  I have found suggestions for using Styrofoam blocks in underground wall construction.  These are a bit more precise, like North Dakota may need them, while Texas might not.  To decide between earth sheltered and earth beamed homes; to decide if a central AC is needed, I'd feel better if I had an energy demand calculated for typical and extreme summer and winter days. 

Q: My husband and I are in the process of purchasing an earth home. The radon testing revealed radon level of 12. How can we mitigate the radon without losing all the benefits of an earth home?

A: (Paul Shippee) First you have to determine where the radon is coming from. Is it coming our of the earth materials (including any concrete) such as walls or floor? Or is it coming in through cracks in the building envelope that are in contact with the surrounding earth? Case 1. a good grade of latex paint will block radon coming off walls and floor materials. Case 2. caulk all cracks and then retest to see if radon levels have been brought down below the threshold level of 4 pc/l

Q: I currently live in a 1960's ranch style house. It is brick on the outside. Have you every heard of someone berming dirt up to the side of a brick house for insulation? It is a pier and beam. I was thinking of doing 2 sides. I also was looking into a sod roof. Do you know where I could find information on this?

A: (Paul Shippee) You could probably berm up a few feet safely on brick siding but beware of water and moisture damage against any wood parts. Earth is heavy and needs to be supported in special ways for anything on the roof... just add attic insulation for that part. There are many books out there... search under "earth shelter" or "underground homes." I built one in Colorado called the SunEarth Home because it was also passive solar heated, a true minimal energy use dwelling. The plans are available at http://www.dreamgreenhomes.com and it is included in some of the earth shelter books you can find.

Q: Wow Kelly, this site prepares even inquistive people such as myself about all the aspects of sustainable housing. Currently I'm looking at some property in my region, Northest Louisiana which is environmetnally challenged. Our climate during the months of May - October can be quite brutal i.e. hot, humid & most of the time mosquito & insect infested. Also during the 1940's/50's some areas of my city was swampland. My question is which example of natural building would you suggest for my area?

A (Kelly): Since the greatest challenge in this zone is keeping cool enough, I believe that one of the best ways to do this is to go underground, if this is possible at the specific site where you would build. In a hot climate, you would want to orient the window areas primarily away from where the sun would penetrate them, unless you need some passive solar heating during the winter months. If your site is on swamp land, you can elevate the building, and berm it with soil brought in.

Q: I have a really crazy idea, and was wondering if it would be possible, and if there are any special precautions I would need to take. I own a 16 X 80 mobile home (7 yrs. old), and I would like to build steel inforced concrete around it and atop it, and pour earth over it, leaving only an added on brick entry room visible. I live in Texas; it is mostly hot and humid. I am a single Mom of two children, and we are on a very tight budget, but want our home to be secure from hurricanes and tornadoes. Would this be really expensive? Would I have to worry about it being damp? Would I save on central air/heating?

A: (Paul Shippee) your idea would, yes, be very expensive... and what about windows?

A (Kelly): It does seem possible to me to do something like this, and it certainly would save on utility costs and make the building more secure from natural disasters once it were accomplished, but actually doing it could be rather tricky, and the result might be rather dark inside the mobile. The weight of pouring concrete directly on the roof might well crush it, so you would have to engineer forms to support this while it cured. Ventilation would also be an issue, so this would have to worked out. The cost of doing all of this could be considerable, but I can see the temptation, since you would be preserving all of the amenities of the mobile intact. If you want to proceed with this idea, I suggest that you consult with an engineer about it.

Q: I just want to know if earth-sheltered houses can be constructed anywhere. For example can they be constructed in Pueto Rico? What about global warming? Does that affect the temperature underground? Let's say that the house was constructed in a mountain side, with heavy rain, is the house safe?

A (Kelly): In general, earth-sheltered housing is appropriate in almost any climate, since the earth helps buffer or moderate the temperature extremes. The affect of global warming will be much less noticable underground than above ground. With all earth-sheltered designs, careful attention must be placed on proper drainage at the specific site where it is built, taking into account the type of soil, the water table, and the nature of the terrain.

Q: I am fifty years old and about to embark on upon a new life. This involves a new home. I live in north east Alabama. I have had a four thousand foot lake house. It is too much house and too much heat here. We want an underground home. I have seen a few in my area and they are OK. I went searching today and found so many beautiful functional underground homes. If you have any sites that I should look at or just any information. We are just getting started. If there are any tips on land. Like buy a hill, mountain, field, forrest, etc. I just need help.

A (Kelly): Generally, picking a good site for underground building involves making sure that the drainage is good and the the water table is not too high. This often means that higher ground is preferable to lower ground. I like the idea of digging into a south-facing slope in regions where passive solar heating is desirable, but that may not be the case in Alabama.

Q: I am currently in my last year in BS Architecture in the University of the Philippines and my thesis is on "Earth Sheltered Housing in the Philippine Setting". I'd like to know if earth shelters are really as efficient in hot-humid climates as they are in most western countries...or if they are, at all, advisable in a country like ours? I have great interest in earth shelters and believe that they are do-able in a hot-humid country like the Philippines but my thesis faculty adviser seems to discourage me. I have been working very hard to have a full understanding of earth shelters and would like to know if this effort will not go to waste. I CANNOT mess up my last year in college. This is seriously do or die for me...Your expert advise could save me.

A: (Paul Shippee) There is plenty of information on earth-sheltered homes in various books and conferences that you could review to boost your (and your advisor's) confidence. In the USA, in Texas which is hot and humid, there are several examples of earth-sheltered homes that greatly reduce both heating and cooling electrical energy needs. Some of these homes are in books that you could access. There is no reason to avoid earth shelter in your climate unless it is hot all year and you ventilate with open walls.

Q: We were looking at the "Sunworks Solar Greenhouse"... We read that it will generate 100,000 BTUs of heat and were wondering what that meant as far as how much the house would save with this form of supplemental heat?

A: (Paul Shippee) It saves 80% of what would otherwise be the heating bill.

Q: I have always liked earth homes and last year I finally bought one. I guess my home is described as a berm home. It is built into a hillside and 3 walls are below ground with the south facing wall open and made of brick. It has a regular pitch roof with trusses and shingles. My question is about insulation. Our home is all electric with a forced air furnace. With power rates climbing so fast our heating bill has skyrocketed. I have about 12 inches in the attic so I think that is OK. But the walls have none. Should there be any wall insulation or would that prevent the earth from cooling the home in the summer. We live in southern Illinois so we have a wide range of tempratures.

A:(Paul Shippee) I would look into glazing the south brick walls, first of all, to capture solar heat for the winter season.  Are the brick walls solid brick or façade only? How high up do the EWN berms go on the brick? I would need a clearer picture and answers to these questions to say anything further...

The south facing brick wall is façade, brick on the outside and frame and drywall on the inside. The berm is to the top of the walls. The gutter on the north side (back) of the house is about 8 inches above the ground. On each end of the house the front wall extends out past the house about 10 feet, so the berm is to the top of the walls all the way to the front. I would like to make the house as well insulated as possible. I'm thinking of adding an outside wood/pellet burner for heating next year. Is that feasible?

I think you need to insulate the side walls down about half way to a minimum of R20. Also, if you want to capture heat from sun on the south bricks you can cover them with glass and vent the day heat into the house. Since the brick is only a façade and insulated inside, then no Trombe wall effect can be achieved.

Q: I am interested in alternative building techniques that will withstand hurricanes and high humidity as I live in northwest Florida. I have looked at the earthships but since I will probably be building this myself and am in my early 50's I would prefer something a little less labor intensive, I cannot swing a sledge hammer to tamp the tires:) I also would like to earthshelter the dwelling and grow a garden on the roof. I'm looking for something that would provide good insulation so that I could save or perhaps eliminate the need for airconditioning. My partner is extremely skeptical of the whole idea (especially the part about me building it myself:) I was wondering about buying a conventional house and encasing it in earthbags and then berming it. Do you have any suggestions?

A: (Kelly) Your idea of earthberming to provide a cooler space and roof garden is excellent. The best technology to accomplish this is a hard to know, especially since you want to do the construction yourself. You're right that pounding tires for a traditional earthship is very difficult labor. You could build an earthship using earthbags instead of tires, and that would be easier, since you don't have to pound the bags so vigorously...but it is still work, as is most any method of construction. Earthships do not generally provide for rooftop gardens, though, as they are designed for rainwater catchment.

The engineering for earthsheltering is obviously critical for their success, so a good design will be needed. The idea of buying a conventional house, covering it with earthbags, and then berming it could easily lead to disaster, as well as a lot of extra work and expense to build. I suggest that you find a well-designed house plan that would suit your needs that is already engineered for earthberming. I have several such homes listed at http://dreamgreenhomes.com/styles/earthsheltered/livingroofs.htm .

Q: I was wondering if there might be a way to build an underground room and/or addition under an existing double wide home? Possibly using a spiral stairway to connect the underground addition to the upstairs? I am in the state of Florida.

A: (Paul Shippee) Anything is possible, it's all a matter of expense - which you will have to estimate locally. You'd have to analyze structurally how you would support the home while digging the hole!!! Not impossible at all, but adds expense.

Q: We have built a Quincy building (steel arched building) and intend to cover it with straw bales followed by earth. Should we protect the metal with a plastic sheet? Should we put anything over the straw before covering it with earth? Are air spaces betweet straw bales and the metal building a problem since everything will be covered with earth?

A: (Paul Shippee) You do not need to protect metal with plastic -in fact leave it out, as it blocks moisture transfer (if there is any). Air spaces are not a problem... Covering everything with earth allows the entire strawbale and earth composite to breathe moisture. Is the structure adequate to hold the amount of earth you are placing?

Q: I am seeking lending institutuons that will hold mortgages on earth sheltered homes.

A: (John MacMillian) color="#006600"> I'm sorry to say that most banks still take a dim view of earth sheltered homes. Many will make a loan for one, but will likely appraise it as a "finished basement". They do not have an open mind. In fact, a few years ago, I took out a home equity loan and they insisted I get fire insurance - for an indestructible home that is made of 120 yards of concrete!

Q: Could you please tell me where I can find an insurance broker that insures earth shelter homes in Tennessee?

A: (John MacMillian) Allstate provided insurance for me. As with the bank, they consider it a finished basement. To tell the truth, up until I took out a note on the property, I never had insurance on the home (the contents yes). For almost 15 years, I was willing to be self-insured, so to speak. The way my home is designed and built, it can't burn, an earthquake (not likely in this area - should not harm it), it's well above the flood plane, 100+ mile per hour winds and hail have done no damage..... In a few years, when the note is paid off, I'll be dropping the insurance!

Q: I live in Beautiful Boston! I was wondering if you happen to know if there are any areas in the North East that allow earth sheltered homes?

A: (John MacMillian) Building codes differ from area to area; but I don't know of any place that specifically prohibits earth sheltered homes in all areas. There may be restrictions in subdivisions, and within city limits, but there should be some residential and/or rural areas where they would be allowed. You will need to call the building commission for each area for which you have an interest. Best of luck with your search!

Q: I'm a final year student studying architecture. My thesis topic is underground architecture. I would like to know about the HVAC systems adopted in underground construction..(especially AC systems)

A: (Kelly) One of the beauties of underground housing is that they often do not require air conditioning because the subterranean climate is so much cooler than the open air, and if it seemed necessary to install such a system, it could be sized much smaller.

Q: Any weird dreams, sense of foreboding, earthquake pre-knowledge, strange noises emanating from the earth, living in earth homes? Any radon, unwanted creepy-crawlies, snakes, flooding, claustrophobia (or does one have a sense of security)? What about radio reception, TV? What about lightening, thunder? Do you hear animals go overhead. Say, wouldn't it be neat to devote one of the underground rooms to having an in-ground-under-ground pool or tennis court? What about escape hatches, or secret passages to the surface? Having a cellar would be moot, but one must have one, I should think- (we're all becoming Hobbitized), it would be like having a closet, filled with veggies and fruits, and jars with tasty things in them.

A: (Kelly) Living in earth homes tends to be very QUIET. It is more like being very secure, and if built correctly there should be no flooding nor unwanted creepy-crawly things. They can be designed to have a very open and airy feeling about them. Radio and TV waves can often still make their way through windows. I don't think that lightning would be problem since the home is exceptionally well-grounded. It would depend on how deep the earth-sheltering is how much one might hear animals, thunder, etc. Large spaces, like for a pool or a tennis court would be difficult, or at least very expensive, to build. Escape hatches and secret passages are all possibilities...and having Bilbo Baggins' fully stocked pantry is a must!

Q: I'm very interested in this type of home, but I'm having a difficult time locating Canadian builders that do earth sheltered homes. I've heard about Earth Equity Building in Canada, but they are from TN. Do you have any Canadian builders in Alberta?  

A: (Paul Shippee) I do not know of any earth builders in Canada. However when I built the SunEarth House in Colorado in 1978, I did not know any earth builders here either. However, using research, building savvy, engineering skill (hired) and willing workers, one can build an earth home anywhere.

Q: I live in Australia and my parents have recently purchased a property in a rural, mountain area where the climate varies considerably from snow in winter (only light and quickly melts) to 40 Deg C in Summer. The property has an existing brick building (that needs work). My parents are concerned about fierce storms and more importantly being energy efficient and self reliant. They have considered digging underground and having a house underground, but I suggested making the most of the house already there by covering it with soil (or something). Time and money are issues. If they used the current house what considerations would they have - structural, effectiveness, etc.

A: (Kelly) Without being able to personally inspect the existing home, it is very difficult to assess how appropriate this might be; there are so many consideration. Depending on various factors, it might be possible to at berm soil around the sides of an existing brick home. This would probably involve some redesign of doors and windows, and some careful analysis of the strength of the walls to withstand the pressures of soil; it may be necessary to reinforce or buttress some walls. As for the roof, this is the most critical part of any underground structure, and most roofs are not designed to handle the weight and potential leakage of earth-sheltering. It might be necessary to either rebuild the entire roof structure, or at least modify it substantially...or the roof could be left as is and improved with better insulation and make it more storm resistant.

And would this provide the protection from the elements (especially the wind)?

Earth berming can reduce the impact of wind on a house considerable, and of course a completely underground house is nearly impervious to wind.

What would be the best way to cover the house (preferably with some earth for planting) without compromising the structural integrity?

See my note above about this. Most underground buildings use reinforced concrete for the roof, but it is also possible to make an earth-sheltered roof using post and beam construction, with appropriate layering of moisture barriers, drainage material, and soil.

If they dug underground, what is the quickest and easiest method to look into. One idea they had was burying several shipping containers and having them connected. Would this be safe/possible?

I do believe that one could safely bury shipping containers to make a home. These units are being used more all the time for residential use. (see this article ) One would need to be careful about exactly how to best protect the steel from any moisture intrusion. Another possibility would be to bury a prefabricated steel vaulted building (like a quonset).

Q: I've noticed that most of the Earthships I find on the net are in the southwest or other warmer to dry regions. How do you think an Earthship or Underground home would do in Northern Wisconsin or Minnesota. I'm planning on building one in that area and I'm a bit worried about keeping it warm through the long winter.

A: (Paul Shippee) There is no reason an underground home would not function well in your climate. It will function well. This presumes that all due attention is applied to considerations of heat loss, proper insulation, and solar gain if desired.

Q: My husband and I have lived in our earth home for three years. The roof is a flat roof that has just rotted out. I was wondering if you would possibly have any suggestion for a new roof?

A: (Paul Shippee) Apparently you have (had) a wood roof, since it rotted. Is the structure that is holding up the earthen roof intact
  or is there a structural hazard? Sounds like you may have to dig up the dirt on the roof to see the condition of the waterproofing. Better remove all the dirt and check every square foot. Then add 6-8 inches of foam board and leave the dirt on the ground, unless you really want an earthen roof; then you have to pay to remedy the leaks, put in new waterproofing, ascertain if the structural supports are safe, etc... In other words, think about why you want an earthen roof?  Is it worth the expense? Good foam board (not the bead board kind) will insulate your roof better. Then you can leave the earth berming at the walls in place.

Q: We're interested in an underground shelter, but we live in central Florida, with very sandy soil - any suggestions?

A (Kelly): I can see no problem in going underground in sandy soil; it actually can be an advantage because it drains water readily.

Q: I truly feel that the world is going to come to an end soon, and all I know is that I want to do everything I can to try to avoid it. I know nothing about building homes let alone homes built underground. Do you think building a home underground could save people from the end?

A: (Kelly) There are a lot of reasons to dig into the ground for housing, and many of these reasons could make life more possible under dire circumstances.

Q: Just wanting to know what earth temperatures are at what depth--in other words--how deep before I get to 55 degree air in a 90 degree AZ climate?

A: (Kelly) I don't have a chart outlining underground temperatures in various parts of the country. My understanding is that, in general, once you get below about 5-8 feet below the surface, the temperature remains constant most of the year...but what that temperature is various from region to region. My guess is that in Arizona this temperature might be closer to 60 degrees F....but that is just a guess.

Q: We live in tornado alley (Oklahoma) and although we have looked at every alternative building style out there, I can't find one that provides the energy efficiency and safety from the weather like an earth bermed home. I've helped a couple of friends build their homes and to be completely honest, I simply do not want to have to go that route again. I've pondered many a night about the viability of using a very well built manufactured home (like a Solitaire) and perhaps using stacked concrete block or earthbags along the sides and an arched concrete roof 'over' the manufactured roof and then berming the house and covering it with sod. To date, I've not found anybody on the net who has already done this and have wondered what your thoughts would be on such a project. I understand that there would be a lot of retrofitting of plumbing vents and I would have to maintain the crawlspace underneath. Basically, I'd have to 'encapsulate' the home tightly in an earthbermed shell, allowing for the existing windows and doors, etc. But since the Solitairs come with Hardyboard cement siding, double pane, insulated windows, R30 in the ceiling, R13 side walls and R15 floors, they're already well, insulated and they are built as well, if not better than many 'stick built' homes in our area. It just seems that ANYTHING above ground is fair game for twisters. Plus the extra insulating factor of an earthbermed home is so appealing. We seriously considered a 'culvert' style home very similar to military bunkers, but again, after helping friends build their homes, I'm simply burned out, and we really can't afford to hire contractors.

A: (Paul Shippee) Sounds good to me...and very doable if you pay close attention to details, and plan well in advance all aspects
...because you are marrying two very dissimilar construction modes. Sounds like a great idea, especially for protection against those tornadoes. The Hardy board siding should make mating with earth easier and lend confidence to the project. My single best advice is to hire a local structural engineer to design the arch and any other structural safety items. You need first to be concerned about safety with overhead heavy materials, and then there’s the tornado lifting forces!

Q: I have 10 acres in Texarkana, TX. I want to have an earth bermed home. I can't find a local company that does this. There are some in Texas but it will add to the cost of my home. Would an adobe home be a good alternative?

A: (Paul Shippee) Adobe will lose more heat...but seems you are in a mild climate where heating is not as important as cooling; if you have a good local source of adobe blocks, that would work; the big cost is in the transportation if far away. Two adobe block thick wall would be excellent. Cost??

Q: I live in the Imperial Valley of California and I decided to have a underground living space to avoid the heat. I was surprised when in a 9 ft. deep by 11 ft. round hole the temp. felt hotter. I got a temp. 15 to 20 degrees cooler but the humidity went from 20% outside to 50% in the hole. I have not started any construction and the hole is in a natural state. I have read about no problems of ground humidity in the desert. I have read about all the waterproofing techniques but I would like to understand if it would solve the humidity in the hole.

A: (Paul Shippee) Often when the temperature cools, the relative humidity increases. If the temperature continues to cool, the moisture in the air condenses (rain). So, that could be one source of the hi humidity reading (assuming you humidistat is accurate) Sometimes in the desert the water table underground can be shallow and this would contribute to higher moisture...underground moisture. Yes, even in the desert. You need more data on this, locally. Building a house down in the dirt is not the same as your hole. The house will be protected from earth moisture, and ventilated with desert air.

I have heard there is a shallow water table here.The main point of the hole was to escape the heat during parts of the day. Due to the moisture and earthquake probability I am going to sink my 28 ft houseboat into the hole and cover it.

Sounds like an interesting project...a cool desert boat!

Q: Wanting to build an underground shelter in Oklahoma in red clay. Circular, vertical walls, about 15 ft deep. Inside support will be a pole barn style to support roof (poles, with lava rock insulation on top covered with 2"concrete). We are wanting to use volcanic rock along outside for insulation. My question is can we use JUST bags filled with rocks for walls? Or do we have to do a layer of clay filled bags then layer of rock filled bags? Plastic will be on outside of coarse.

I forgot to mention that the diameter of the shelter is going to be 40 ft with interior walls to add more support. Also if we can use just volcanic rock does it have to be in bags? My husband was pondering the poles spaced 4 ft apart on walls, then a layer of chicken wire(or stronger wire) then an empty space 10" wide, more chicken wire (supported by smaller poles), then plastic around that. Then filling in empty space with rock and of coarse backfilling. Is this possible? It would make it quicker and easier.

A: (Kelly)You should be able to just use the lava rock filled bags all the way up your wall. This would give you about 14" thick walls, which is pretty good insulation. On the other hand, if you do as your husband suggest, you would end up with somewhat thinner walls, but this might be fine, since the underground temperature in OK is around 62 degrees F.

Obviously, whatever mesh you use to contain the lava rock needs to be small enough to keep the rock from spilling out. When I built my earthbag house using scoria, I used 3/4" minus crushed stone, which would have spilled out of chicken wire. A somewhat courser grade would likely do fine with your plan, or you could use a finer mesh.

Q: What do you recommend to control condensation and levels of humidity in the interior with hot, humid air hitting a cold wall of earth? Are there any earth bermed houses in hot, humid climates that don't need air conditioners, dehumidification, or mechanical ventilation?

A: (Kelly) Scientific studies have shown that earthen wall materials provide one of the best ways of mitigating humidity in a house. They can absorb and release a great deal of humidity without ill effect. So if there is a thick earthen plaster that is not sealed and can breathe this would be best. And if there are earthbags filled with earth behind the plaster, this would give another level of protection.

I'm in the awkward in-between climate of Virginia - four seasons, but hot and humid in the summer. Any recommendations for that? We already utilize passive solar design and high levels of insulation, but with hot nights and no air conditioning, it's barely cooler inside than out. We'd love to try to get the temperature down a bit more (thus the investigation of digging into the ground) but are loath to use much (if any) electricity to do so.

The average underground temperature in Virginia ranges from 59 to 61 degrees F., so digging into the ground will certainly cool you off. The question is what to do about the humidity? Well, I wouldn't necessarily expect it to be any more humid in a subterranean house than one stuck up in the atmosphere; the same air circulates both. What about the potential for condensation on the cooler walls of a subterranean house? If those walls were actually at 60 degrees, you would still not get any condensation, even at 100 percent humidity. If it were me I would go underground for greater comfort.

Q: Are there any type of alternative building codes or permitting for off grid, geothermal homes? I'm building my home with ICF, 8 ft below the surface. Living roof, geothermal heating and cooling, etc. I live in N. Florida and the County Permitting office is making life tricky for me. I will work through all of the conventional coding problems, but its become costly and time consuming.

A: (Paul Shippee) I don't know how or if they are restricting you, or just asking for proof of concept type calculations? Anyway, best bet is to work with them, show your best intention to make the home safe, etc. Many times we can learn things from them if we do not resist them. I know of no separate alternative building codes for your situation, but continue to search for them, and also take the attitude of teaching the bullding officials to widen their perspective while keeping things safe, which is their main job, I think. We are all on a learning curve with alternatives, and they should be included in the learning. Manage that attitude and things will shift for you.

Q: I'm entertaining the idea of building a small cut-and-cover rock and concrete house in a steep hillside. Enclosed space would be 300 to 700 square feet, and would be accessed off a 100 sq. ft. porch. Most of the walls would be completely underground except for the ones adjacent to the porch. The house would be completely electric free, and would function more as a weekend retreat than a house. With typical insulation(2-4" polystyrene outside the rock walls and above the concrete ceiling), I expect very little condensation issues during occupancy, since the fireplace(s) would be going almost constantly, I'd guess. The problem is that the house would likely sit unoccupied for extended periods, with no heat source and no method of dehumidification. This is the relatively humid Virginia Piedmont region. Looking at history charts, the dew point is always below the daily average temperature. In the summer, the dew point and the min temp will coincide briefly on most days. My thinking is that with free airflow through the house(crack a window open and open the fireplace damper), The masonry envelope will be the same temperature as the average daily temperature. Hopefully, it will even be holding some residual heat by early morning when the condensation risk is the greatest. Is this correct reasoning? Are there other considerations for controlling humidity in a non-electric and frequently unoccupied "cave" house?

A: (Paul Shippee) I agree with your reasoning and the probable outcome it predicts with the small airflows you describe. But you are also letting moist air in too? It seems that if the insulated walls get much cooler than the outside ambient air they will drip with condensate. Do you expect the outside air with it’s humid moisture load to leak into the cave house? Caves are often dripping with moisture due to earth moisture or humid air that enters the cooler earth temps. You seem to be hoping that the concrete walls will stay at temps above the dew point, right? I wish you had said that the porch faces South and there are large windows to let the sunshine in to warm the concrete, but you did not say that? What about that? Probably you could dig a space into the earth at your site and observe the condensate before you build?

Q: Just curious how deep would it have to be to take advantage of the constant ground temperature?.A walapini is deeper than an Earthship, therefore more constant temperature.

A: (Kelly) It is my understanding that at about 6 feet below the surface the temperatures are quite stable, although this varies somewhat from place to place.  Shallower depths may vary only slightly.

Q: We bought a home in the mountains of Colorado. It had been a modular built on a walkout basement. The modular was removed, and we are now using the walkout basement to build essentially an earth berm home. No water issues to speak of in the walkout basement previously. The uphill wall is completely underground, and each of side walls are underground to halfway along the wall. The downhill wall is entirely exposed. Any suggestions for what eco friendly flooring works best in these types of homes? It will be used only seasonally so will have big internal temp changes.

A: (Kelly) If there are currently no water issues that is a good indication that the basement was originally built well. If there is already a concrete floor, you could just keep it that way, or cover it with a variety of flooring materials, including tile, brick, earthen, etc. If the floor is currently dirt, then I would suggest placing a moisture barrier down, insulating it with crushed scoria or commercial foam panels, and then putting a durable flooring over that as suggested above. If the floor gets sunshine during the day, some of that heat can be retained with the heavier mass materials.

Q: My husband and I are thinking about buying a passive solar earth sheltered home built in the 70's in Falmouth, Massachusetts. While visiting, we noticed a moldy smell. If there is a problem other than just old carpets or paint, is there a way to restore/renew/renovate? We are neophytes with no experience.

A: There are many possible causes for the moldy smell: poor or no insulation around the footings or under the floor, poor ventilation, or, hopefully, age, which you suggest in your question.  This could be a risky purchase, although a modern ventilation system may be what is needed. I'm sorry that I can't offer more on this. but I have only your short report to go by.

Q: We had someone tell us this: “Green roofs are very expensive and prone to problems (supporting water laden soil along with winter freeze thaw). Usually used on corporate, government and high end residential projects.” I could see the possible future moisture problems maybe, especially if that wasn’t carefully mitigated in the beginning by attention to constructing it correctly. But I thought living roofs were one of the least expensive choices. May we have your opinion on this?

A: (Kelly) Living roofs do need to be very carefully constructed to make sure they are adequate to support the weight and arranged with components that assure that moisture does not migrate beyond the soil or growing medium. They are not as straightforward to build and maintain as common roof designs, and for that reason they can be more expensive. What they add is aesthetic pleasure and benign ecological value.

Comment (Kelly): In reading through some of your introductory comments at endeavourcentre.org about foundations, I came across your statement: "In much of North America, foundations have been twinned with conditioned, subgrade living space: the basement. In many markets, having a basement is so normal that it can be hard to convince a homeowner to imagine a house without one. It is difficult to create a sustainable basement and — unless the home is in the driest, best draining of soils — impossible to create a basement that doesn’t rely on several layers of petrochemical products to stay dry"

While I agree that there are definitely challenges in building ecological basements, I question your suggestion to avoid them altogether. From my perspective the value of below-grade living space is extremely high, what with the moderating effect this has on creating comfortable living temperatures, and thus the energy inputs required for both heating and cooling the space. Nearly everywhere on Earth digging into the ground has the potential to save energy and create more comfort. I consider it one the most sustainable of all building practices, especially as we go forward with our changing climate.

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