The Earth as the Perfect Blanket Loren C. Impson c.1992 Loren C. Impson For the past several years, I have observed structures as they slowly deteriorate through the actions of the wind, sun, moisture, and other natural enemies of wood-framed houses. This observation has led me to these rules: heat with the sun, cool with the wind, and protect the home with a blanket of earth. Nature's actions become my friend instead of my enemy, and I am left to enjoy the beauty of the landscape. In all earth sheltered structures, the soil moderates the inside temperature from the outside blazing sun or icy wind, acts as an infiltration barrier, dampens sound, and discourages vandalism. How revolutionary is this idea of earth sheltered housing? How long has this technology been tested? In Tunisia, the Romans built their courtyards on the ground surface and their homes below for protection from the severe heat. In central Turkey, archeologists have unearthed 41 earth sheltered cities. Kansas City, Missouri has a growing industrial park where over 100 companies have rented and bought space in solid limestone, 50-200 feet into the earth. St. Pierre de Feric, France is the site of 47 homes built into a 45 degree slope. Sacramento, California has an 180,000 square foot earth-sheltered state office building. Our two communities of earth sheltered homes north of Denton, Texas are merely another affirmation that earth sheltering is becoming popular again. What is Earth Sheltered Housing? The term Earth Sheltered Housing (ESH) most appropriately defines all types of homes built with the earth as a key design element. ESH's vary in relationship to the earth. Below grade describes a structure built in a hole in the earth and then covered to return the site to its original state. Recessed means cut into the side of a hill. Bermed involves pushing earth against the sides, but leaving one or more sides exposed. An atrium is built with the primary view areas of the home turned inward to create a central courtyard; this form of structure can be either below grade or bermed. Earth-covered means putting a blanket of earth on the roof of a structure built on grade. Benefits of earth Building using earth offers a long-lived, affordable, and low tech shelter. Most people in our society want to own their home, yet many cannot afford the expense. By reducing the cost, we can make this dream more viable. The expense of owning a home includes the initial construction cost, interest on the loan, and insurance for disasters. Then we have the monthly utility bills and increased maintenance as age and the mortgage near their terms. Building an earth-sheltered home can be an inexpensive solution for those who don't have a lot of money but have some time. The cost depends on the materials and the amount of excavation of the site. Scrounging materials and borrowing a few friends' time can reduce the cost. A 1500 square foot home in Arkansas took three months, four primary people (including myself, extra friends needed for the heavy stuff), and $25,000 for material and some labor. The structure consisted of three reinforced-concrete domes Ð one dome 32 feet in diameter, a 20 foot dome, and another 20 foot dome with an 8 foot extension. By reducing the initial construction costs, interest and mortgage costs are then reduced. Maintenance is reduced since painting and roofing are not necessary. Protection from natural disasters is another benefit of an Earth Sheltered House; danger from windstorms, fire, hail, and earthquakes is virtually eliminated if the structure is properly built. Insuring just the contents of the structure will reduce insurance costs. The blanket of earth over a home can reduce the amount of heating and cooling necessary in most climates, thus reducing utility bills. Utility bills can be eliminated with the use of photovoltaic cells, a wind generator, hydroelectric power, and/or solar heating. An ESH can occupy sites normally unacceptable to other types of construction. Malcolm Wells, a noted ESH architect, built his office near a freeway to demonstrate the sound deadening qualities (and because the price was right!) Choosing a Site Selecting a site for the earth sheltered home involves deciding where and how the house will be built, for example, into the side of a hill, or on a flat plain (not in a flood plain!) The next question is how to excavate the site. You may cut into a south facing slope, build the house, then recover it and integrate it back into the natural landscape. How much of the house will be earth-covered should be determined. Think of how any exposed areas will be finished Ð with windows or decorative stone, or back-filled with earth and then held on the house with retaining walls. The design of the house must include a provision to remove water. Don't put yourself down into a hole. A lot of people think underground homes are like bomb shelters. Back in the early '80's, we decided to call them Earth Sheltered Homes because the earth is used to protect you from the elements. You don't have to bury yourself in a hole, a couple of feet will do just fine. If you insulate this house as mentioned later in the text, you should be comfy year 'round. Materials What types of materials are appropriate for a home that is to be covered to some extent with earth? Judging from the materials I've seen in use, just about any material. Fiberglass-coated plywood, treated wood, and stone are examples, but concrete is my favorite. Concrete is the most durable and the most formable. It will not rot; it won't burn. Concrete can be poured in forms or shot onto a form. Domes are made from a concrete shell on a rebar framework. The material list includes concrete, reinforcing bar, chainlink fencing, extended metal lathing, wood for scaffolding, and tools for putting it all together. Curved homes Ð domes or free-form shapes Ð are most easily built shooting concrete onto an inflated form. Soil The home needs to be designed to rest comfortably on its footings. The expansivity, percolation rate, and load bearing capacity of the soil all need to be determined. When you have this information in hand then you are ready to design the foundation and the drains. Waterproofing Waterproofing seems to be most people's greatest concern, but moisture can be completely controlled. I believe in redundancy and use several systems. One system, a French drain, ensures that water cannot enter via the floor. A French drain consists of a perforated pipe Ð like that used for a septic drain field Ð surrounded with gravel. This drain is placed around the structure's perimeter at a level below the footings to quickly divert a rising water table away from the structure. Another method prevents water entering from the roof of the structure. The exterior of the concrete shell is painted with a pargetting (water resistant plaster) coat to fill any surface cracks and damp-proof the structure. The walls should then have a sheet of plastic laid against them. Earth-covered houses have another layer of protection. A layer of earth covers the concrete shell, then a layer of insulation and plastic is added, followed by more earth. This plastic layer runs into another French drain perimeter further from the structure. Thus, any surface water that should penetrate this deep is allowed to percolate down to the French drains. Two feet of the best soil available is placed over the final layer of plastic for growing ground cover or a garden. Plants are chosen which have a root structure that does not penetrate more than eighteen inches. Plants with a good root structure will slow the percolation of the rain water. Rainwater seldom penetrates below six inches into the normal lawn.The foliage will help cool the structure in the summer and if mulched will insulate in the winter. LIKE, TRY TO INSERT SECOND GRAPHIC HERE, DUDE Thermal Mass Energy cost reduction is often the most appealing feature of ESH. Placing the home in the earth reduces air infiltration. The mass of the structure and the earth surrounding it provide thermal lag to moderate the temperature year round. Thermal mass measures how well a material holds energy as heat. When the sun shines on a stone, the stone holds or absorbs heat. In the evening, the stone lets off this heat. Weight is a good indicator of thermal mass. Heavy objects usually hold more heat than lighter ones. Earth sheltered homes use lots of material (earth) which absorb heat during the day and release it at night. Different materials have different heat storing capacity. When a curtain interrupts the sun, the curtain picks up some heat, but doesn't have the capacity to store this heat. Thus heat is convected into the room. Thermal lag refers to the amount of time it takes for a material to absorb and release heat. When the sun shines on the earth in the summer, heat builds up and eventually works its way down into the soil. By fall that warmth has penetrated deep into the soil. The warmest time for soil ten feet down in the earth is October. The same effect is reversed in winter, so that the loss of heat makes the soil ten feet down the coldest temperature in May. In the same way, the house creates a micro-thermal lag effect from within. If heat is picked up during a sunny December day, that heat is stored in the structure and surrounding soil for the night. During summer months, any interior heat generated or collected is eliminated at night by ventilation and by evaporative cooling from watering the rooftop gardens. Insulation High thermal mass ensures the capacity to store a lot of heat, but insulation can prevent the stored heat from escaping. The insulation system we use is directly from John Hiat's Passive Annual Heat Storage. When the desired shape of the structure has been achieved with gravel and dirt, place layers of polyethelene plastic and styrofoam over the earth in the shape of a sloped hill. This insulation is placed at a two foot depth (or deeper depending on frost line) then covered with plastic. He suggests going 20 feet beyond the foundation to encapsulate a large quantity of earth. The thermal mass of the earth under the insulation holds the desired heat in the house; the plastic sheeting protects from unwanted moisture. Let there be light Light and ventilation are two important elements of a living environment and are normally achieved with windows. Windows need to be oriented to allow for sunlight and breezes at the appropriate time of year. At the planning stage, note where the sun rises and sets at the extremes (the 21st of June and December) and note seasonal wind patterns at the site. Design windows so that summer sun does not enter but winter sun is available for solar heating. We are fortunate in this part of the country to have prevailing summer winds from the south. Cross ventilation is provided as needed by vents Ð either skylights or doors Ð placed high in the structure. Plan the location of trees. Look at some of the books on this topic Ð Ed Mazria's Passive Solar Energy Design is one of the best. Conclusion Overall, the advantages of Earth Sheltered Housing are exciting and persuasive Ð low construction cost, reduced energy costs, elimination of costly and time consuming maintenance chores, and the safety and security of underground protection. The residents in such dwellings enjoy the rewards of the state of the art technology that is in harmony with Ð not in conflict with Ð the natural environment. Let the sun shine, the wind blow, and the water flow clean! Access Author: Loren C. Impson, Sun Life Homes, Rainbow Valley, Rt. 2 Box 28-8, Sanger, TX 76266 ¥ 214-704-0922 Insulation: John Hait's Passive Annual Heat Storage from the Rocky Mountain Research Center, POB 4694, Missoula, MT 59806. ("How to store summer's sunshine to keep your wigwam warm all winter." I paid $15 for the book, shipping was extra.) Permaculture: Bill Mollison's Permaculture: A Designers' Manual from local bookstore or Tagari Publications, POB 1, Tyalgum, NSW, Australia 2484. (How your home fits into your environment Ð as Architectural Graphics and Standards is to architecture, so is Permaculture to self- sufficient homesteading.)