Earth shelter - WikiHQ

thumb|upright=1.5|An earth sheltered house in Switzerland ([[Peter Vetsch) ]]

An earth shelter, also called an earth house, earth home, earth-bermed house, earth-sheltered house, earth-covered house, or underground house, is a structure (usually a house) with earth (soil) against the walls and/or on the roof, or that is entirely buried underground.

Earth acts as thermal mass, making it easier to maintain a steady indoor air temperature and therefore reduces energy costs for heating or cooling.

Earth sheltering became relatively popular after the mid-1970s, especially among environmentalists. However, the practice has existed for nearly as long as humans have been constructing their own shelters.

Definition

"Earth-sheltering is <nowiki>[...]</nowiki> a generic term with the general meaning: building design in which soil plays an integral part." This definition is problematic however, since earth structures (e.g. rammed earth or cob) are not usually considered as earth shelters as they are above ground.
"A building can be described as earth-sheltered when it has a thermally significant amount of soil or substrate in contact with its external envelope, where “thermally significant” means making a functional contribution to the thermal effectiveness of the building in question.
"The use of earth cover to moderate and improve living conditions in buildings."

Design and construction

Design

Earth sheltered homes are often constructed with energy conservation and savings in mind. Specific designs of earth shelters allow for maximum savings. For bermed or in-hill construction, a common plan is to place all the living spaces on the side of the house facing the equator (or north or east, depending on latitude). This provides maximum solar radiation to bedrooms, living rooms, and kitchen spaces. Rooms that do not require natural daylight and extensive heating such as the bathroom, storage, and utility room are typically located on the opposite (or in-hill) side of the shelter. This type of layout can also be transposed to a double level house design with both levels completely underground. This plan has the highest energy efficiency of earth sheltered homes because of the compact configuration as well as the structure being submerged deeper in the earth. This gives it a greater ratio of earth cover to an exposed wall than a one-story shelter would.

The soil type is one of the essential factors during site planning. The soil needs to provide adequate bearing capacity and drainage, and help to retain heat. With respects to drainage, the most suitable type of soil for earth sheltering is a mixture of sand and gravel. Well-graded gravels have a large bearing capacity (about ), excellent drainage and a low frost heave potential. Sand and clay can be susceptible to erosion. Clay soils, while least susceptible to erosion, often do not allow for proper drainage, and have a higher potential for frost heaves. Clay soils are more susceptible to thermal shrinking and expanding. Being aware of the moisture content of the soil and the fluctuation of that content throughout the year will help prevent potential heating problems. Frost heaves can also be problematic in some soil. Fine grain soils retain moisture the best and are most susceptible to heaving. A few ways to protect against capillary action responsible for frost heaves are placing foundations below the freezing zone or insulating ground surface around shallow footings, replacement of frost-sensitive soils with granular material, and interrupting capillary draw of moisture by putting a drainage layer of coarser material in the existing soil.

Water can damage earthen shelters if it ponds around them. Avoiding sites with a high water table is crucial. Drainage, both surface and subsurface, must be properly dealt with. Waterproofing applied to the building is essential.

Atrium designs have an increased risk of flooding, so the surrounding land should slope away from the structure on all sides. A drain pipe at the perimeter of the roof edge can help collect and remove additional water. For bermed homes, an interceptor drain at the crest of the berm along the rooftop's edge is recommended. An interceptor drainage swale in the middle of the berm is also helpful or the back of the berm can be terraced with retaining walls. On sloping sites, runoff may cause problems. A drainage swale or gully can be built to divert water around the house, or a gravel-filled trench with a drain tile can be installed along with footing drains.

Soil stability should also be considered, especially when evaluating a sloping site. These slopes may be inherently stable when left alone, but cutting into them can greatly compromise their structural stability. Retaining walls and backfills may have to be constructed to hold up the slope prior to shelter construction.

On land that is relatively flat, a fully recessed house with an open courtyard is the most appropriate design. On a sloping site, the house is set right into the hill. The slope will determine the location of the window wall; the most practical orientation in moderate to cold climates is a south-facing exposed wall in the Northern hemisphere (and north-facing in the Southern hemisphere) due to solar benefits. The most practical orientation in the Tropics nearest the equator is north-facing toward the aphelion (or perhaps northeast) to moderate the temperature extremes. Just outside the Tropics, the most practical way to avoid afternoon heat excess may be an east-facing house or, if near a west coast, exposure of the east end and the west end, with the two long sides embedded in the earth.

Depending on the region and site selected for earth-sheltered construction, the benefits and objectives of the earth shelter construction vary. For cool and temperate climates, objectives consist of retaining winter heat, avoiding infiltration, receiving winter sun, using thermal mass, shading and ventilating during the summer, and avoiding winter winds and cold pockets. For hot, arid climates objectives include maximizing humidity, providing summer shade, maximizing summer air movement, and retaining winter heat. For hot, humid climates objectives include avoiding summer humidity, providing summer ventilation, and retaining winter heat.

Regions with extreme daily and seasonal temperatures emphasize the value of earth as a thermal mass. Earth sheltering is most effective in regions with high cooling and heating needs and high-temperature differentials. In regions such as the southeastern United States, earth sheltering may need additional care in maintenance and construction due to condensation problems in regard to the high humidity. The ground temperature of the region may be too high to permit earth cooling if temperatures fluctuate only slightly from day to night. Preferably, there should be adequate winter solar radiation and sufficient means for natural ventilation. Wind is a critical aspect to evaluate during site planning, for reasons regarding wind chill and heat loss, as well as shelter ventilation. In the Northern Hemisphere, south facing slopes tend to avoid cold winter winds typically blown in from the north. Fully recessed shelters also offer adequate protection against these harsh winds. However, atria within the structure can cause minor turbulence depending on the size. It is helpful to take advantage of the prevailing winds in the summer. Because of the limited window arrangement in most earth shelters, and the resistance to air infiltration, the air within a structure can become stagnant if proper ventilation is not provided. By making use of the wind, natural ventilation can occur without the use of fans or other active systems. Knowing the direction, and intensity, of seasonal winds, is vital in promoting cross ventilation. Vents are commonly placed in the roof of bermed or fully recessed shelters to achieve this effect.

Building materials

The selection of construction materials should consider the type of structure, site characteristics, climate, soil type, and design. Stronger, longer-lasting building materials are required for structures that are buried deeply. Waterproof and insulated materials should also be utilized to withstand the pressure and moisture of the surrounding ground. For instance, concrete and reinforced masonry, wood, and steel are all viable materials. Concrete is the most common choice for earth-sheltered buildings due to its strength, durability, and fire resistance. Cast-in-place concrete is employed for non-critical structural elements such as concrete foundations, floor slabs, and exterior walls with less than of earth cover. In contrast, precast reinforced concrete can be used for floors, walls, and roofs. Concrete masonry units should be or greater, with the use of “A” or “H” facilitating unit placement around vertical reinforcing bars, depending on the required structural integrity. It is typically advised to use Type S mortar, grout with a minimum strength of , and a concrete slab with a minimum strength of and thickness. Brick or stone masonry reinforced with steel bars can be utilized for walls that will be subjected to lateral or vertical pressure from earth cover. Masonry generally costs less than cast-in-place concrete. Wood can be widely employed in earth-sheltered buildings for structural and internal work, including floors, roofs, and exterior walls. However, wooden frame walls, which must endure lateral pressure, are limited to a burial depth of one story when used as a structural material. Beyond this depth, the cost will rapidly increase while using wood as a structural material. Although wood can be less expensive than other materials, it lacks steel's strength, therefore it might not be the ideal option for structural material in some earth-sheltered dwellings, especially in moist soil type. Steel is used for beams, columns, bar joists, and masonry reinforcement. The advantage is that steel has high tensional and compressional strength, while the disadvantage is that it must be protected from corrosion if it is exposed to air, water, or other chemicals. It must be used effectively because it is also expensive.

Excavation

In earth-sheltered construction, there is often extensive excavation done on the building site. An excavation several feet larger than the walls' planned perimeter is made to allow for access to the outside of the wall for waterproofing and insulation.

Foundations

Once the site is prepared and the utility lines installed, a foundation of reinforced concrete is poured. The walls are then installed. Usually, they are either poured in place or formed either on or off-site and then moved into place. Reinforced concrete is the most common choice. The process is repeated for the roof structure. If the walls, floor, and roof are all to be poured in place, it is possible to make them with a single pour. This can reduce the likelihood of there being cracks or leaks at the joints where the concrete has cured at different times. The foundation of the buildings designed by Vetsch are built conventionally.

Walls

Several different methods of external (load-bearing) wall construction in earth shelters have been used successfully. These include concrete block (either conventionally mortared or surface-bonded), stone masonry, cordwood masonry, poured concrete, and pressure-treated wood. Others advise the use of timber framed, gable roofs of pitch at least 1:12 to promote drainage.

Types

Three main types of earth shelter are described. Due to the building being above the original ground level, fewer moisture problems are associated with earth berming in comparison to underground/fully-recessed construction, and it costs less to construct. constructed in the middle of the shelter to provide adequate light and ventilation. The atrium is not always fully enclosed by raised ground, sometimes a U-shaped atrium is used, which is open on one side. However, the atrium does tend to trap air within it which is then heated by the sun and helps reduce heat loss. Atrium designs are well suited to flat sites,<!-- Schools, commercial centres, government buildings and other buildings could be built underground. The main component of it is an insulated and waterproof "umbrella" which extends out from the earth shelter for several meters in all directions. Hence the term "umbrella house". The earth under this umbrella is kept warm and dry relative to surrounding earth, which is subject to constant daily and seasonal temperature changes. This creates a large heat storage area of earth, effectively a huge thermal mass. Heat is gained via passive solar in the earth shelter and transferred to the surrounding earth by conduction. Thus, when the temperature in the earth shelter dips below the temperature in the surrounding earth, heat will return to the earth shelter. After a time, a stable temperature is reached which is an average of annual heat changes in the external environment. Some criticize the technique (along with the earth sheltering technique as a whole), stating concerns including difficulty and expense of construction, moisture and lack of evidence.

Annualized geo solar

Another design aimed at passive seasonal energy storage, annualized geo solar is sometimes applied to earth shelters.

Earth tube ventilation

Passive cooling which pulls air with a fan or convection from a nearly constant temperature air into buried Earth cooling tubes and then into the house living space. This also provides fresh air to occupants and the air exchange required by ASHRAE.

History

Early history

thumb|right|Mandan lodge, North Dakota. c. 1908

thumb|right|"The interior of the hut of a [[Mandan Chief": aquatint by Karl Bodmer from the book "Maximilian, Prince of Wied's Travels in the Interior of North America, during the years 1832–1834"]]

thumb|Turf house in Sænautasel, [[Iceland.]]

Earth sheltering is one of the oldest forms of building. It is thought that from about 15,000 BC migratory hunters in Europe were using turf and earth to insulate simple round huts that were also sunk into the ground. The use of some form of earth sheltered construction is found across many cultures in history, distributed widely across the world.

In China, man-made cave dwellings have been used as a shelter since 2,000 BC. In certain areas of northern China, like the provinces of Shaanxi and Shanxi, since the loess earth is structurally uniform and compacted, providing easy access to good quality building material with stable structure, earth-sheltered homes have been in use for centuries.

1970s–1980s heyday

The 1973 Oil Crisis saw the price of oil dramatically increase, which influenced vast social, economic and political changes worldwide.

As early as the 1960s in the US, some innovators were designing contemporary earth shelters.

He also claimed the view from a window below the ground was better than that from other windows, and that the flooring he used in his an underground home (plastic sheeting over bare dirt) was "superior" to what is elsewhere available. Consequently, the temperature at the surface may vary considerably according to the day / night cycle, according to weather and particularly according to season. Underground, these temperature changes are blunted and delayed, termed thermal lag. The thermal properties of earth therefore mean that in winter the temperature below the surface will be higher than the surface air temperature, and conversely in summer the earth temperature will be lower than the surface air temperature.

Indeed, at a deep enough point underground, the temperature remains constant year round, and this temperature is approximately the mean of summer and winter temperatures. Below this level the temperature increases on average every due to heat rising from the interior of the Earth. Traditional wood structure home requires lumber for framing and interior finishes, which is quite a big demand. Soil as the main building material and blending in with the landscape, earth-sheltered houses drastically reduce the demand for lumber.

Biological effects

Earth homes organically embrace animals and poultry as well as water, soil, and plants. Arcology studies the relationship between animals and plants and man-made buildings during ecological development. For example, raising poultry and domesticated animals is an important part of the traditional Chinese rural human settlements and these elements create a stable and sustainable ecological cycle that benefits the environment.

Landscape protection and land use

Compared to conventional buildings, earth houses can fit into their surroundings. The soil-covered roofs hide the building within the landscape.

Some claim that the construction method is advantageous to the nitrogen-fixation of the soil on the roof, because it would otherwise be covered by the foundation of a traditional house. Contrary to conventional roofs, earth-house roofs allow plants to grow semi-naturally on them.

Earthquake protection

While residents of earth sheltered homes report noticing more minor earthquakes, the homes are resilient against large earthquakes, as their subterranean nature allows them to move with the earth. Picture a small twig house sitting on top of a tub of dirt: Shake the dirt, and the house will dance and stress. But if you bury the house in the dirt, you can shake the tub without stressing the house as much.

Roof planting

Roof covering is done using the excavated material, in which plants can be planted. or require this type of property to be common for the area.

Design complexity

Overall it is more technically challenging to design an earth shelter compared to a regular home. Because of the unorthodox design and construction of earth-sheltered homes, local building codes and ordinances may need to be researched and/or navigated. Many construction companies have limited or no experience with earth-sheltered construction, potentially compromising the physical construction of even the best designs. The specific architecture of earth houses usually leads to non-righted, round-shaped walls, which can cause problems concerning the interior decoration, especially regarding furniture and large paintings.

Repairs to the walls are very difficult to service; and may require re-evaluating and rebuilding the house from scratch.

An earth shelter cannot be enlarged with an extra room - this will require breaking the waterproofing sealant cladding the concrete walls of the building.

Sustainability

In "green building", four "lifetime" phases of a building are described, namely material sources, construction, in use, and deconstruction (life-cycle assessment). Terms carbon zero and negative carbon buildings refer to the net greenhouse gas emissions over these four phases. Questions therefore arise as to whether certain structures are truly environmentally friendly. For example, raw materials must be extracted from the earth, transported and then manufactured into building materials and transported again to be sold and finally transported to the build site. A lot of fossil fuels may be used during each of these stages.

Earth sheltering often requires heavier construction materials to resist the weight of the earth against the walls and/or roof. Reinforced concrete in particular needs to be used in much larger quantities per building. The manufacture of concrete is a major source of greenhouse gases.

The materials involved tend to be non-biodegradable substances. Because the materials must keep water out, they are often made of plastics. The excavation of a site is also drastically time- and labor-consuming. Overall, the construction is comparable to conventional construction, because the building requires minimal finishing and significantly less maintenance.

Moisture and indoor air quality

Problems of water seepage, internal condensation, bad acoustics, and poor indoor air quality can occur if an earth shelter has not been properly designed and ventilated. Very high humidity levels can allow mold or mildew growth, associated with a musty smell and potentially with health problems. The below-ground orientation of many earth-sheltered homes can allow accumulation of radon gas (which is known to increase the risk of lung cancer) or other undesirable materials (e.g. off gassing from construction materials).

The threat of water seepage occurs around areas where the waterproofing layers have been penetrated. Earth usually settles gradually. Vents and ducts emerging from the roof can cause specific problems due to the possibility of movement. Precast concrete slabs can have a deflection of 1/2 inch or more when the earth/soil is layered on top of them. If the vents or ducts are held rigidly in place during this deflection, the result is usually the failure of the waterproofing layer. To avoid this difficulty, vents can be placed on other sides of the building (besides the roof), or separate segments of pipes can be installed. A narrower pipe in the roof that fits snugly into a larger segment of the building can also be used. The threat of water seepage, condensation, and poor indoor air quality can all be overcome with proper waterproofing and ventilation.

Limited natural light

Despite large windows (usually facing south in the Northern Hemisphere), many earth-sheltered homes have dark areas in the areas opposite the windows. All natural light coming from one side of the home can give a "tunnel or cave effect".

Risk of collapse

Reports of collapse seem to be rare. In one case, an author and proponent of earth sheltering died when an earth roof he designed collapsed on him.

Limited escape routes

Compared to above ground house, earth-shelters may have limited escape routes in case of emergency,

"The Burrow" in Canterbury, UK designed by Patrick Kennedy-Sanigar.
There are 2 earthships in the UK, at Fife, Scotland and the Earthship Brighton in England.
"The Underground House" in Great Ormside, Cumbria. Two storey earth shelter built in a disused quarry.
Malator, Pembrokeshire. Built for former Labour MP Bob Marshall-Andrews in 1998.
Undermill, Bushey Heath Watford, Hertfordshire, Build 1996 modern earth sheltered building 4 bedroom 170m2 in the UK.

United States

Bill Gates' house, on the shore of Lake Washington (Medina, Washington, USA). This is a well-known example of an earth-sheltered home.
Forestiere Underground Gardens in Fresno, California.
Underground House Colorado in Ward, Colorado, was a subterranean dwelling known for its architectural design.
Underground House Las Vegas in Las Vegas is based on the designs of Jay Swayze.
Underground World Home, was a home designed for the 1964 New York World's Fair by architect Jay Swayze.

Gallery

File:Earth house estate.JPG|Earth house estate in Dietikon made by Peter Vetsch

File:EarthShelterRestAreaOH.JPG|Earth Sheltered rest area along Interstate 77 in Ohio, USA

File:Underground World Home exhibit.png|Underground World Home exhibit, New York

File:Underground House Las Vegas.jpg|Underground House Las Vegas

</gallery>

Notes

References

Berge, Bjørn. The Ecology of Building Materials. Architectural Press, 2000.
Campbell, Stu. The Underground House Book. Vermont: Garden Way, Inc., 1980.
De Mars, John. Hydrophobic Concrete Sheds Waterproofing Membrane Concrete Products, January 2006.[http://www.concreteproducts.com].
Debord, David Douglas, and Thomas R. Dunbar. Earth Sheltered Landscapes. New York: Wan Nostrand Reinhold Company, 1985.
Edelhart, Mike. The Handbook of Earth Shelter Design. Dolphin Books, 1982.
Miller, David E. Toward a New Regionalism. University of Washington Press, 2005.
Reid, Esmond. Understanding Buildings. The MIT Press, 1984.
The Underground Space Center University of Minnesota. Earth Sheltered Housing Design. Van Nostrand Reinhold Company, ed. 1978 and ed. 1979.
Wade, Herb, Jeffrey Cook, Ken Labs, and Steve Selkowitz. Passive Solar: Subdivisions, windows, underground. Kansas City: American Solar Energy Society, 1983.

External links

Appropedia article on Earth-Sheltered Building
StocktonUnderground : An Owner-Builder Approach
Earth-Sheltered Houses
Earth houses by Vetsch Architektur
Self-heating eco-house by Veljko Milković

Earth Homes Now

de:Erdhaus