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Design Considerations for Earthsheltering |
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Q: We are planning to build a home in northern Wisconsin and are trying to decide between single story earth sheltered or earth sheltered basement plus one story. Do you know of any studies which have been done comparing energy costs and building costs between structures (in areas with very cold winters)? A: (Leonard Jones) The best analysis of energy use in severely cold climates that you might find useful is in James Kachadorian's book, "The Passive Solar House." This book walks through several examples of estimating the energy use for houses located in cold climates and discusses some construction ideas that you may find interesting I can tell you with some assurance that a house with basement will cost more than one without, but the additional space has a much lower cost per square foot than the primary floor. However, building costs in general vary all over the place from one season to the next and from one part of the country to the next. If you are planning to contract for the construction, I'd suggest that you develop a couple of plan alternatives and approach a local contractor for his estimate of cost. If you are going to do the owner-builder thing, you'll have to estimate the quantities of materials and obtain costs from local suppliers. A: (Mike Oehler) I know of no such studies. Why in the world go above ground when you can get all the wonderful benefits of earth sheltering and still have an abundance of light, air and great views? Q: I am looking to build a house in Oregon, and would like to make it so it doesn't take away from the environment, or hurt the surrounding forest. Can you suggest some material we can use and if the saturated ground could withstand having a house under-ground. A: (Kelly) If you are looking to build an earth-sheltered home in a wet climate, this can be done as long as the site isn't a perpetual swamp. Care must be made to design the house to mitigate against possible moisture problems. The best materials to build with underground are those that could not be adversely affected by moisture, such as earthbags, stones, or even ICFs (insulated concrete forms). Q: Is it possible to have 2 stories underground, and what would you, if you could, build it out of? A: It is possible to have two stories underground, but it is not feasible (ie, too expensive) for a residence. The structural, excavation, and waterproofing costs would be way too high. This kind of construction is done only for large commercial buildings. They are always made from heavily reinforced thick concrete. Q: I'm doing some research into building a small earth sheltered home in the Southeastern US. The space will be about 25 - 30' wide and a bit less deep. I am thinking of pouring walls about 12" thick and backfilling them on three sides, southern front, etc. Then for the roof, I would like to make a form, temporarily supported from below that is the shape of an acute arch, maybe how a bridge is arched over a waterway to resist collapse or maybe even a bit more. I have done some rough calculations with this and I am in the ballpark, but would like to see some info from a CE or an architect as well. I am thinking the roof will need to be 12" - 14" thick to support 3' of earth on top and allow for a safety margin for water, etc.. The roof can be permanently supported in the middle from underneath if necessary, but I would prefer to keep the design free span. I am pretty good with trig and calc if you can point me in the right direction or give me some formulas to work with so I can calculate for live load, dead load, span, thickness, etc. A: You seem to be on the right track with an arch-shaped roof. However, the dead loads are enormous: 3 ft dir t= 300psf, 1 cu ft water = 62 psf, 12" concrete = 140 psf, TOTAL = 500 Lb/sq ft, this is 5 times a normal roof loading. I suggest you hire a structural engineer, P.E. licensed for liability and have him design the rebar and concrete recipe, and most especially the structural "connections" between wall and roof.. all this trouble is well worth it when considering the extreme safety concerns of such a building. Q and A (Kelly): I am the father of two young daughters and we are getting evicted from our N.Y.C. apartment. I have a small patch of land situated on the top of a shale mountain near Albany, N.Y. To get the material for a road to the site a semi-circular pit was mined into the S.W. side of the slope. Because stone is such a good conductor will I still get the benefits of a "real earth" bermed design: especially heat in the winter! A: You certainly will get the advantage of berming, even into solid stone. I once visited a home in Utah that had been excavated from a solid rock cliff face, and was told that the indoor temperature varied little from about 65 degrees F. all year round. You will likely want to have some insulation between the shell of your house and the backfilled material to be able to better control the exact indoor temperature. Also: Since the rock wall is pitched back can I get 2 stories underground (without the sagging weight of earth against the structure)? Without knowing more about the exact conditions of the site, it is hard for me say, but I would expect that if the excavated stone face is fairly stable, then you would really only have the weight and pressure of the backfill material to withstand. I would advise that you consult with a local engineer about the specifics of the design. Would a curved foundation wall in the back help direct water away from the structure? This might be true, depending on the details of how the site is drained. Perhaps equally importantly, a curved wall will much better withstand the pressure from the berm than a straight one would. Q: My wife and I live in Matamoros, Tamaulipas just across the border from Brownsville, Texas. We pastor a church and are ready to start building a larger building to seat 500 or so, with classrooms, offices, etc. As you can imagine heat is the main factor here. Stifling, humid heat! We only have maybe 15 days a year when it gets cold. We are 20 miles or so from the beach so we do get a nice sea breeze that we want to take advantage of but not sure how to do that. Our water table is high so in-ground building is probably out of the question. Although we don't know much about construction other than the typical "block kiln" type that is so prevalent around here, we are certainly thinking outside the box. One thing we have in surplus are many willing hands to work. Are there any suggestions you might have for us or possibly any book you might refer us to? A: Even with a high water table, it is possible to take advantage of earth-sheltered building, by simply berming with soil that is brought to the site. So any of the books listed at on the keep cool page might be helpful. Also, there are some concepts used in Middle Eastern areas that capture prevailing breezes with "wind catchers" that channel the breeze past pools of water to help cool the house. I know I have seen them described, but I can't remember where at the moment. Q: Do you think that Energy-10 would be a good program to evaluate a small earth sheltered home? I have tried Equest but the wizards are too limited to model anything involving earth sheltered elements. I want to know what I can achieve before I build. A: I am not familiar with energy-10 but if it contains steady state heat transfer assumptions, then it would not be adequate to analyze heat flows in an earth sheltered building --unless some pretty educated modifications are applied to the equations. This is because of the thermal storage dynamics of the earth materials and how this impacts the diurnal temperatures driving the heat losses of the building. Q: I have acreage in Little Switzerland, NC and am considering the feasibility of building an earth-sheltered home there someday. Is that an area where you have experts or familiarity with the terrain or have you seen any built there? A: (Kelly) While I am not specifically knowledgeable about your area, I would say that an earth-sheltered home can be built almost anywhere that potential water problems can be dealt with, such as high ground water or saturated soils. Q: Years ago I came up with an idea for a rather large underground home. The basic shape is like a large baseball diamond. On the bases are large silos constructed of cement (home plate) other for bases. My question is... what sort of construction materials would be strong enough to withstand the soil and a New England winter snow load on the roof. Is this a viable layout? The size of the interior I see as nearly 2 acres. Now I am off to buy a lottery ticket. A: Reinforced concrete in a dome or other curved shape is best for the structural loads you describe. Q: My project is an underground museum. My teachers are asking me only one question: How will I provide ventilation to the museum? A: (Kelly)
There are many ways to provide fresh air ventilation in an underground building. Air ducts can be provided, windows and skylights can be operable, the design can include an atrium that is either open-air or has ventilation built into it... Q: I am planning on eventually building a house in the lower hills of the Cascade mountains, an hour or so outside of Portland OR. I would like to utilize an earthen design, along with solar power for the house. It would be a two story log cabin style reinforced with concrete with a berm on the back end of the house which would face uphill. Ideally I would like the top of the house to be earthen as well and try to flow rather naturally into the upward sloping forest of the mountain. The three remaining sides will be open and the front would face downhill to the south. With these designs in mind it will require that quite a bit of earth removal be done and an almost 25 ft. retaining wall be built for the back or bermed end of the house. I am concerned with issues of having to dig this deep and running into bedrock, and also whether the retaining wall would be able to withstand pressures of so much earth behind it. I have considered creating a more "stepped" design with the lower level protruding about another 10-15 ft. downhill and the upper level being recessed further into the mountain so as to follow the natural gradient of the mountain and require less excavation. Do you feel that this design is practical at all? If so do you have any suggestions that would help? A: (Mike Oehler) Sounds to me like the disastrous "First Thought House" which is what I have been trying to get people NOT to do since 1972. This is the design which has kept underground housing from becoming the raging success that it deserves to be. I advise you to read "The $50 & Up Underground House Book" and to view "The Low Cost Underground House Workshop and Shelter Seminar" videos. |
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Paul Shippee is director of Colorado Sunworks and is a solar designer and builder. He was the founding President of the Colorado Solar Energy Association, and a teacher. Paul holds a degree in Civil Engineering, with a major in Structural Engineering from the University of Connecticut. He helped plan housing experiments in energy conservation with the U.S. Department of Housing and Urban Development, and designed and built the SunEarth House, which was the best-rated energy conservation, earth-sheltered home in a HUD-sponsored study. He holds a U.S. patent on a solar water heating system. Paul is currently living in a rammed-earth/strawbale home that he has designed as a personal residence in Colorado. His book, THE LANGUAGE OF SOLAR ENERGY: Heat Loss & Solar Gain for Buildings, is available from his website: 
