DOE/GO-10097-373 FS 120 ENERGY February 1997 EFFICIENCY AND

RCLEARINGHOUSEENEWABLE Earth-Sheltered ENERGY Let’s assume you’re in the market for a Beginning Your Project, and Cost—will new . Let’s further assume that, like answer some questions you may have. many other people, you’re concerned Once you’ve decided on an earth- about the limited supplies of domestic oil sheltered , the sections on Design, and gas, the unpredictable cost, and the Construction Considerations, including loca- environmental price tag attached to the tion, climate, site, and , and Construc- continued use of these fuels. tion Materials can help you make the house a reality. Is there any way to reconcile your con- cerns and still build your dream home? Advantages The solution might lie in earth-sheltered There are many advantages to earth- housing. These structures offer many sheltered construction. An earth-sheltered energy-efficient features and are often home is less susceptible to the impact of designed to use solar energy for heating extreme outdoor air temperatures, so you and cooling. Some designs make use of won’t feel the effects of adverse weather recycled materials in their construction. as much as in a conventional house. Tem- peratures inside the house are more stable If you do your homework, earth-sheltered than in conventional , and with less construction can be an attractive and temperature variability, interior rooms rewarding choice in housing. The follow- seem more comfortable. ing sections—Advantages, Disadvantages, NREL / PIX02909 This house in Tempe, Arizona, uses earth-sheltered construction methods to help decrease cooling costs.

NT O ME F E T N R E A R This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. P G

E Y D The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiency

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A N and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on C I I T R E information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC. D E M S A TAT ES OF Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

Because earth covers part or all of their construction. Securing financing may also exterior, earth-sheltered houses require be easier if you work with those who have less outside maintenance, such as painting firsthand knowledge of earth-sheltered and cleaning gutters. Constructing a construction and its benefits. house that is dug into the earth or sur- rounded by earth builds in some natural Cost soundproofing. Plans for most earth- Comparing cost factors for an sheltered houses “blend” the building into earth-sheltered house to those for building the landscape more harmoniously than a a conventional house can be like compar- conventional home. Finally, earth-sheltered ing apples and oranges. Costs vary by houses can cost less to insure because their region, depending on the area’s construc- design offers extra protection against high tion activity and cost of materials. Many winds, hailstorms, and natural disasters earth-sheltered houses are built by their such as tornados and hurricanes. owners and are customized in different Disadvantages ways, adding amenities that can dramati- cally increase final costs. As with any type of unusual construction, there are some disadvantages associated However, when you factor costs, remem- with earth-sheltered housing. Principal ber to consider important expenses that downsides are the initial cost of construc- occur over the life of a house, such as exte- Earth-sheltered tion, which may be up to 20% higher, and rior maintenance and utility costs. Greater the level of care required to avoid mois- initial investment can actually mean your houses moderate the ture problems, during both the construc- ongoing costs, such as heating, cooling, tion and the life of the house. It can take and maintenance, will be reduced. Making impact of extreme more diligence to resell an earth-sheltered the best use possible of natural resources home, and buyers may have a few more may be one of an earth-sheltered house’s outdoor temperatures hurdles to clear in the mortgage applica- greatest advantages. Therefore, in compar- tion process. ison to standard houses, while earth shel- so that the interior ters tend to be slightly more expensive to Beginning Your Project build, these higher initial costs may be offset by the lower energy costs after com- remains at a You may want to start your project by con- pletion. And while energy savings have tacting the organizations that can help you been documented by families living in relatively constant locate architects, builders, and contractors earth shelters, attributing that savings with earth-sheltered building experience solely to the earth-sheltered design would temperature. (a few are listed in the Source List). The be difficult, because most earth-shelters experienced builders in your location can incorporate a wide variety of energy- also ensure that construction plans meet efficient features. area building code requirements, which can depend on a local official’s interpreta- Design tion. Earth-sheltered designs can present some potential difficulty, such as confor- There are two basic types of earth-sheltered mance to minimum window sizes in each housing—underground and “bermed” (or room prescribed by fire codes or building banked with earth). Certain characteristics codes. Other problematic areas are roofing such as the location and soils of your site, specifications and insulation requirements the regional climate, and design prefer- specified by codes; earth may or may not ences are central to which type will work be considered an acceptable substitute for best for you. materials specified. Builders can inform you of the local guidelines, and may also provide cost comparisons between earth- sheltered housing and conventional hous- ing in your area.

Using experienced professionals will reduce your personal time investment in researching details of earth-sheltered

2 Since at least part of Underground housing means an entire walls that give exposure to daylight. This structure built below or completely design uses a subgrade open area as the the earth-sheltered underground. A bermed structure may entry and focal point of the house. It is be above grade or partially below grade, built completely below ground on a flat house is covered with with outside earth surrounding one or site, and the major living spaces surround more walls. Both types usually have earth- a central outdoor courtyard. The windows earth, it usually covered roofs, and some of the roofs and glass doors that are on the exposed may have a vegetation cover to reduce walls facing the provide light, solar requires less exterior erosion. heat, outside views, and access via a stair- way from the ground level. Atrium/court- maintenance such as From these two basic types, three general yard homes are usually covered with less designs have been developed. They are the: than 3 feet (0.9 meters) of earth primarily painting and gutter because there is no benefit in energy effi- • atrium (or courtyard) plan—an under- ciency from greater depths. This style also cleaning than does a ground structure where an atrium offers the potential for natural ventilation. serves as the focus of the house and the conventional home. entry into the dwelling; The atrium design is hardly visible from • elevational plan, a bermed structure that ground level and barely interrupts the may have a glass south-facing entry; landscape. It also provides good protec- and the tion from winter winds and offers a pri- • penetrational plan, which is built above vate outdoor space. This design is ideal for or partially above grade and is bermed an area without scenic exterior views, in to the exterior walls that are not dense developments, and on sites in noisy facing south. areas. Passive solar gain—heat obtained through windows—might be more lim- An earth-covered dwelling may have as ited, due to the window position in an little as 6 to 8 inches (0.2 meters) of sod or atrium plan. Courtyard and as much as 9 feet (2.7 meters) of earth cov- snow removal are important items to con- ering the structure. An atrium design sider in design. offers an open feeling because it has four

Barely visible above ground, the atrium design provides good protection from weather extremes.

3 Usually set into the side of a hill, the elevational design exposes one face of the house and covers the other sides—and perhaps the roof—with earth.

The elevational and penetrational plans usually built at ground level, and earth is are more conventional earth-sheltered built up (or bermed) around and on top of housing designs. Elevational plans expose it. This design allows cross-ventilation one whole face of the house and cover the opportunities and access to natural light other sides—and perhaps the roof—with from more than one side of the house. earth. The covered sides protect and insu- late the house. The exposed front of the Construction Considerations house, usually facing south, allows the The climate in your geographical area will sun to light and heat the interior. The floor determine whether an earth-sheltered plan is arranged so common areas and Using designers and house can be a practical housing solution. bedrooms share light and heat from the Studies show that earth-sheltered houses southern exposure. This type of house builders experienced are more cost-effective in climates that may be placed at varying depths below have significant temperature extremes and ground level and is usually set into the with earth-sheltered low humidity, such as the Rocky Moun- side of a hill. The view provided will be tains and northern Great Plains. Earth one of landscape, rather than open sky, as houses can reduce temperatures vary much less than air tem- in the atrium design. A structure designed peratures in these areas, which means the in this way can be the least expensive and the challenges earth can absorb extra heat from the house simplest to build of all earth-sheltered in hot weather or insulate the house to structures. associated with maintain warmth in cold weather. However, the elevational design may have constructing a non- The site’s topography and microclimate limited internal air circulation and reduced determine how easily the building can be daylight in the northern portions of the conventional house. surrounded with earth. A modest slope house, although there are ways to alleviate requires more excavation than a steep one, these problems by using skylights. The and a flat site is the most demanding, wide design of the house can be offset by needing extensive excavation. A south-fac- close attention to architectural details, ing slope in a region with moderate to landscaping, and exterior materials. long winters is ideal for an earth-sheltered In the penetrational plan, earth covers the entire house, except where it is retained for windows and doors. The house is

4 factor to consider in locating your home. Areas with high concentra- tions of radon can be hazardous, although there are methods that can reduce radon buildup in both conventional and earth-sheltered dwellings.

The groundwater level at your build- ing site is another important consid- eration. Building above the water table is almost A house built in the penetrational design is usually built at ground level and essential. Choosing earth is then built up around and on top of it. a site where the water will natu- building. South-facing windows can let in rally drain away from the building is the sunlight for direct heating, while the rest best way to avoid water pressure against of the house is set back into the slope. In underground walls. The site should be regions with mild winters and predomi- surveyed for low spots and areas where nantly hot summers, a north-facing slope water will collect. Seasonal or regular sur- might be ideal. Every site differs, but gen- face water flows should be channeled erally southern exposures offer more sun away from the structure. Drainage sys- and daylight throughout the year than tems must be designed to draw water north-facing slopes. Most designs can be away from the structure to reduce the fre- built to take advantage of each site. quency and length of time the water remains in contact with the building’s It makes economic The type of at your site is another crit- exterior. Underground footing drains sim- ical consideration. Some types of soil are ilar to or greater than those required by a sense to think beyond more suitable than others for earth-shel- house with a are necessary in tered construction. For example, the best many cases. the initial purchase soils are granular, such as and . These soils compact for bearing the Construction Materials price and consider weight of the construction materials and The construction materials for each type of are very permeable, which means they structure will vary, depending on charac- lifetime energy costs. allow water to drain quickly. The poorest teristics of the site, climate, soils, and soils are cohesive, like , which may design. However, general guidelines show expand when wet and has poor perme- that houses more deeply buried require ability. Soil tests, offered through profes- stronger, more durable construction mate- sional testing services, can determine rials. Materials must provide a good sur- load-bearing capability of soils and possi- face for waterproofing and insulation to ble settlements that may occur. withstand the pressure and moisture of the surrounding ground. When soil is wet Radon is an invisible and odorless or frozen, the pressure on the walls and radioactive gas produced naturally when floors increases. Pressure also increases uranium in rock decomposes. It is found in the soil and in outdoor air in harmless amounts, but can reach dangerous levels when trapped. Radon levels are another

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with depth, so materials such as concrete Concrete can also provide supplemental and reinforced masonry, wood, and steel strength in other types of earthen con- are all suitable. To reduce your transporta- struction. For example, a concrete topping tion costs, it helps if appropriate materials can be added to wooden roof planks, and are locally available. cement “parging” (or coating) can be added to walls with masonry construction Concrete before waterproofing. Concrete is the most common choice for constructing earth-sheltered . Not Masonry only is it strong, it is also durable and fire Masonry (i.e., brick or stone) can be used resistant. Several for walls that will receive vertical or lateral forms of concrete are pressure from earth cover. It is reinforced Building With Soil used. Lightly rein- with steel bars that are put in the core of There has been a recent surge in homes that use soil forced concrete, the masonry in places of high stress, such as a primary building material. This type of con- which is poured and as weight-bearing walls or walls with struction is literally “old as the hills.” Some ancient reinforced at the site, earth against them. Masonry generally architecture, such as the Great Wall of China, shows is used for noncriti- costs less than cast-in-place concrete. the durability of earthen construction. So building with earth and sand, always plentiful and inexpen- cal structural ele- sive, is not a new idea. ments such as Wood concrete founda- Although these houses do not typify the earth- Wood can be used extensively in earth- sheltered construction designs discussed in this pub- tions, floor slabs, and sheltered construction for both interior lication, earth is a major component in their con- exterior walls with and structural work including floors, struction material and many of the same energy less than 6 feet (1.83 roofs, and exterior walls. Wood is attrac- efficient ideas are used. Many buildings in the south- meters) of earth tive for its color and warmth, and comple- western United States use —bricks constructed cover. Precast rein- of tightly compacted earth, clay, and straw—as their ments tile and masonry, as well as main construction material. forced concrete can concrete walls, floors, and ceilings. How- resist loads at any Another building material is “.” This ever, using wood as a structural material process entails mixing earth and cement, and pack- reasonable depth requires wooden frame walls, which must ing it into the wall forms with a pneumatic tamper. and can be used for withstand lateral pressure, be restricted to The result is a rough approximation of sedimentary floors, walls, and a burial depth of one story. Beyond this rock. In fact, this “stabilized earth” achieves com- roofs. Concrete depth, the rapidly increasing cost of wood pressive strengths estimated to be about half that of absorbs and stores concrete. Walls can be made even thicker with little construction restricts most builders from added cost, since the labor and the formwork are the heat, helping to pre- using it as a structural material. Although more costly items of a wall. Although a steel-rein- vent temperature wood can cost less than other materials, it forced, eight-inch (20.32 centimeters) thick earthen swings that can dam- does not offer the strength that a material wall is strong enough for load-bearing walls, extra age some building such as steel does, so it may not be the mass, coupled with good solar design, can offer bet- material. ter insulation and increased heating and cooling best choice for structural material in some capacity. Compared to earth-sheltered houses, addi- houses. Wood must also be treated with tional insulation may not be necessary in rammed- Precast concrete com- preservatives to prevent damage from earth houses, depending on the area’s climate. ponents are cured at moisture. If your structure can make prac- a plant or on-site tical use of wood as a framing material, location before they employing carpenters who can rapidly are used, thereby decreasing construction construct a timber frame for an earth- time and cost in comparison to cast-in- sheltered house can decrease labor costs. place forms. The uses and advantages of precast and cast-in-place concrete are simi- Steel lar, except that precast concrete works best Steel is used for beams, bar joists, in simple or repeatable shapes. Special columns, and concrete reinforcement. It is care must be taken to make the joints particularly useful because of its high ten- between sections watertight. sional and compressional strength. The primary disadvantage of steel is that it must be protected against corrosion if it is exposed to the elements or to groundwa- ter. It is also expensive, so it must be used efficiently to be economical as a structural material.

6 Alternative Construction Materials • Plastic and vulcanized sheets are among A form of earth-sheltered house that has the most common types of underground been receiving much attention is referred waterproofing. Plastic sheets include to as an “.” These houses are high-density polyethylene, chlorinated built to be self-contained and indepen- polyethylene, polyvinyl chloride, and dent; their design allows occupants to chlorosulfonated polyethylene. Suitable grow food inside and to maintain their vulcanized membranes or synthetic rub- own water and solar electrical systems. bers include isobutylene isoprene, Some builders believe they have proven ethylene propylene diene monomer, the design’s ability to tap into the constant polychloroprene (neoprene), and poly- temperature of the earth and store addi- isobutylene. For all these materials, the Climate, soil tional energy from the sun in winter, seams must be sealed properly, or the although a back-up system, usually elec- membranes will leak. composition, tric, may be recommended. • Liquid polyurethanes are often used in places where it is awkward to apply a groundwater levels, These carry out their environ- membrane. Polyurethanes are some- mentally conscious theme by employing times used as a coating over insulation and topography unusual building materials in the form of on underground structures; however, recycled automobile tires filled with com- weather conditions must be dry and rel- affect which type of pacted earth for and struc- atively warm during their application. ture. Aluminum or tin cans are also used • Bentonite is a natural clay formed into earth-sheltered house for filling minor walls that are not load- panels or applied as a liquid spray. The bearing. Foam insulation can be applied to panels are simply nailed to walls; the is best for your site. exposed exterior or interior walls and cov- spray is mixed with a binding agent and ered with stucco. Interior walls can also be applied to underground walls. When drywalled for a more conventional look. the bentonite comes in contact with moisture, it expands and seals out the Other Considerations moisture. Waterproofing Humidity Waterproofing can be a challenge in earth- Humidity levels may increase in earth- sheltered construction. Keep in mind these sheltered houses during the summer, three ways to reduce the risk of water which can cause condensation on the inte- damage in your house: choose the site rior walls. Installing insulation on the out- carefully, plan the drainage both at and side of the walls will prevent the walls below the surface of the house, and water- from cooling down to earth temperature; proof your house. however, it also reduces the summer cool- ing effect of the walls, which may be There are several waterproofing systems viewed as an advantage in hot tempera- currently in use, including rubberized tures. Mechanical or a asphalt, plastic and vulcanized sheets, liq- dehumidifier is often necessary to solve uid polyurethanes, and bentonite. Each the humidity issue. Proper ventilation of has its advantages and the one you choose closets and other closed spaces should will depend on your site and house plan. keep the humidity from becoming a prob- lem in those areas. • Rubberized asphalt combines a small amount of synthetic rubber with asphalt Insulation and is coated with a polyethylene layer Although insulation in an underground to form sheets. It can be applied directly building does not need to be as thick as to walls and roofs and has a long life that in a conventional house, it is neces- expectancy. sary to make an earthen house comfort- able. Insulation is usually placed on the exterior of the house after applying the waterproofing material, so the heat gener- ated, collected, and absorbed within the earth-sheltered envelope is retained inside

7 the building’s interior. If insulating out- bustion gases are directly vented to the side the wall, a protective layer of board outside. In addition, indoor pollutants should be added to keep the insulation emitted by formaldehyde foam insulation, from contacting the earth. Depending on plywood, and some fabrics can accumu- the type of structure—wood, masonry, late and become an irritant if ventilation is concrete, or steel—insulation may instead not properly planned. be placed inside the walls before the waterproofing material is applied. A Home for the Future

Air Exchange/Air Quality If you are looking for a home with many energy efficient features that will provide Adequate air exchange must be carefully a comfortable, tranquil, weather-resistant planned when building an earth-sheltered atmosphere, an earth-sheltered home dwelling. Generally, well-planned, natural could be right for you. With the general ventilation or ventilation by exhaust fans information in this publication and more can dissipate ordinary odors. Any com- details available from the sources listed bustion appliances that are installed below, you are on your way to owning a should be “sealed combustion units,” home that can protect you from the ele- which have their own, direct source of ments and the rising costs of energy and outside air for combustion, and the com- building resources.

Source List Reading List The following organizations can provide you with more The following publications provide further information information on earth-sheltered construction. about earth-sheltered houses. The list is not exhaustive, nor does the mention of any publication constitute a rec- American Underground-Construction Association ommendation or endorsement. 511 11th Avenue South, Suite 248 Minneapolis, MN 55415 Complete Book of Underground Houses, R. L. Roy, Sterling (612) 339-5403 Publishing Co., 1994. Rocky Mountain Research Center Earth Sheltered Housing, G. Klodt, Reston Publishing P.O. Box 4694 Company, 1985. Missoula, MT 59806 (406) 728-5951 Earth Sheltered Housing Design, J. Carmody, Van Nos- trand Reinhold, 1985. Solar Survival Architecture P.O. Box 2009 Earth Sheltered Residential Design Manual, R. Sterling, Van El Prado, NM 87529 Nostrand Reinhold, 1982. (505) 751-0462 Technology, L. Boyer and W. Grondzik, Texas Fax: (505) 751-1005 A&M University Press, College Station, TX, 1987. E-mail: [email protected] Earthship Systems and Components, M. Reynolds, Solar Texas Energy Extension Service Survival Press, 1991. Center for Energy and Mineral Resources Texas A&M University Passive Annual Heat Storage: Improving the Design of Earth College Station, TX 77843-1243 Shelters, J. Hait, Rocky Mountain Research Center, 1983. For information about many kinds of energy-efficient building ideas and renewable energy topics, contact: The Energy Efficiency and Renewable Energy Clearinghouse (EREC) P.O. Box 3048 Merrifield, VA 22116 (800) DOE-EREC (363-3732) Fax: (703) 893-0400 E-mail: [email protected] EREC provides free general and technical information to the public on the many topics and technologies pertaining to energy efficiency and renewable energy.

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