Editing Earth shelter (section)

==Comparison with standard housing==
===Advantages===
In 1981, Oehler promoted his low-budget building design (a simple hole in the ground with walls of wooden planks backed by plastic sheeting) by claiming it needed no foundation, used less building material and labour, had less maintenance, was aesthetically pleasing, had a lower taxation rate in the US at the time, cost less to regulate temperature, was less affected by stormy weather, had pipes which wouldn't freeze where they entered the house, were "ecologically sound", relatively fireproof, soundproof and had an increased garden space as compared to regular house on a similarly sized plot of land.<ref name=oehler1981>{{cite book |author1=M Oehler |title=The $50 and Up Underground House Book |date=1981 |publisher=Mole Publishing Company |isbn=9780442273118 |url=https://www.lowimpact.org/lowimpact-topic/earth-sheltered-houses/ |language=en}}</ref>

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.<ref name=oehler1981/>

He claimed he would provide a built-in greenhouse in the design.<ref name=oehler1981/>

He claimed his homes could be used as fallout shelters in case of nuclear wars and also claimed that, in the case of complete societal collapse, his design would be more defensible than a regular house in the case of random attacks, as well as being better concealed from potential hostiles (without a map and unfamiliar with the area). He believed that underground, inhabitants would be better protected from "atmospheric radiation" ([[Nuclear fallout|fallout]]). Because his design was not waterproofed, one would be "closer to a source of water", and could potentially simply dig a well in the middle of the room.<ref name=oehler1981/>

He furthermore claimed anyone could build one of his designs irrespective of skill or ability for only $50.<ref name=oehler1981/>

====Passive heating and cooling====
[[File:Amplitude dampening phase shifting.jpg|thumb|left|Diagram showing effect of thermal mass and insulation in an earth sheltered structure. ''y''-axis represents temperature; ''x''-axis represents time. Blue line: external temperature fluctuations between day maximum and night minimum (could also represent Summer maximum and Winter minimum temperature fluctuation on a longer timescale). Red line: Internal temperature. 1: Phase shifting (delay between maximum/minimum external temperature and internal temperature). 2: Amplitude dampening (the reduction in maximum or minimum internal temperature relative to that of the external temperature).]]
Due to its density, compacted earth acts as [[thermal mass]],<ref name="roy2006" /> meaning that it stores heat and releases it again slowly. Compacted soil is more of a [[Thermal conduction|conductor of heat]] than an insulator. Soil is stated as having an [[R-value (insulation)|R-value]]<!-- LINK IS CORRECT FOR THIS CONTEXT DO NOT CHANGE TO [[R-value (soils)]] THANKS --> of about 0.65-R per centimeter (0.08-R per 1 inch),<ref name="Hait2013" /> or 0.25-R per 1 inch.<ref name="roy2006" /> Variations in R-value of soil may be attributed to different soil moisture levels, with lower R values as moisture level increases.<ref name="Hait2013" /> The most superficial layer of earth typically is less dense and contains the root systems of many different plants, thereby acting more like [[thermal insulation]],<ref name="roy2006" /> meaning, it reduces the rate of temperature flowing through it.

Approximately 50% of the heat from the Sun is absorbed at the surface.<ref name="BGS">{{cite web |title=BGS Reference and research reports - Ground source heat pumps |url=http://www.bgs.ac.uk/reference/gshp/gshp_report.html |website=www.bgs.ac.uk |publisher=British Geological Survey}}</ref> 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.<ref name=BGS /><ref name=Hait2013 /> Sources vary in their stated values for this deep earth constant temperature (also termed amplitude correction factor). Reported values include {{convert|5|-|6|m|ft|abbr=on}},<ref name="thorpe2018" /> {{convert|6|m|ft|abbr=on}},<ref name="Hait2013" /> {{convert|15|m|ft|abbr=on}},<ref name=BGS /> {{convert|4.25|m|ft|abbr=on}} for dry soil, and {{convert|6.7|m|ft|abbr=on}} for wet soil.<ref>Mechanical and Electrical Equipment for Buildings. Walter T. Grondzik, Alison G. Kwok 2014</ref> Below this level the temperature increases on average {{convert|2.6|C-change|0}} every {{convert|100|m|ft|abbr=on}} due to heat rising from the interior of the Earth.<ref name=BGS />

Diurnal temperature changes between maximum and minimum temperatures can be modelled as a wave, as can seasonal temperature changes (see diagram). In architecture, the relationship between the maximum fluctuations of external temperature compared to internal temperature is termed amplitude dampening (or temperature amplitude factor).<ref name="thorpe2018" /> [[Phase shifting]] is the time taken for the minimum external temperature to reach the interior.<ref name="thorpe2018" />

Partially covering a building with earth adds to the thermal mass of the structure.<ref name="thorpe2018" /> Combined with insulation, this results in both amplitude dampening and phase shifting. In other terms, earth sheltered structures receive both a degree of cooling in summer and heating in winter.<ref name="thorpe2018" /> This reduces need for other measures of heating and cooling, saving energy.<ref name="mcconkey2011" /> A potential disadvantage of a thermally massive building in cooler climates is that after a prolonged period of cold, when the external temperature increases again, the structures internal temperature tends to lag behind and take longer to warm up (assuming no other form of heating).

The reduction of air infiltration within an earth shelter can be advantageous. Because three walls of the structure are mainly surrounded by earth, very little surface area is exposed to the outside air. This alleviates the problem of warm air escaping the house through gaps around windows and door. Furthermore, the earth walls protect against cold winter winds which might otherwise penetrate these gaps. However, this can also become a potential indoor air quality problem. Healthy air circulation is key.

As a result of the increased thermal mass of the structure, the [[thermal lag]] of the earth, the protection against unwanted air infiltration and the combined use of passive solar techniques, the need for extra heating and cooling is minimal. Therefore, there is a drastic reduction in energy consumption required for the home compared to homes of typical construction.

====Wind protection====
The unique architecture of earth houses protects them against severe windstorms. They cannot be torn away or tipped over by strong winds. Structural engineering and, above all, the lack of corners and exposed parts (roof), eliminate vulnerable surfaces which would otherwise suffer from storm damage.<ref name=vetsch1994 />

====Natural resource saving====
Compared with the material needs of standard buildings, earth-sheltered homes can greatly reduce the number of natural resources.<ref>{{cite book  |last=Gideon |first= Golany|date= 1992|title= Chinese earth-sheltered dwellings: indigenous lessons for modern urban design|location= Honolulu |publisher= University of Hawaii Press|page= 178|isbn= 978-0-8248-1369-7}}</ref> 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.<ref name="Jing 1988">{{cite book  |last=Jing |first= Qi min|date= 1988|title= Earth Sheltered Architecture|location= Tianjin|publisher= Huazhong University of Science & Technology Press Co., Ltd |isbn= 978-7-5308-0526-8}}</ref> 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.<ref name=vetsch1994 />

Such houses can also be built as terraced structures on a slope in hilly terrain.<ref name=vetsch1994 />

====Fire protection====
Compared to other building materials, such as wood, earth houses feature efficient fire protection owing both to the use of concrete and the insulation provided by the roof. Taking the example of Earthships, there is a reported case where the structure survived fire better compared to other types of buildings.<ref>{{cite web |title=Earthship buildings are fire resistant, not a total loss. |url=https://pangeabuilders.com/earthship-buildings-are-fire-resistant-not-a-total-loss/ |website=Pangea Builders |date=12 September 2018}}</ref>

====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.<ref name=oehler1981/>

====Nuclear bomb survivability====
Due to the mass of the earth between the living area of an earth house and the surface grade, an earth home offers significant protection from impact/blast damage, or fallout associated with a nuclear bomb.<ref name=oehler1981/>

====Soundproof====
Earth shelters may provide privacy from neighbors, as well as soundproofing.<ref name=oehler1981/> The ground provides acoustic protection against outside noise. This can be a major benefit in urban areas or near highways.

====Architectural aesthetics====
Earth sheltered dwelling express itself with the color harmony of soil and earth.<ref name="Jing 1988"/> Meanwhile, the material properties of soil and earth give earth homes the simplicity of geomatic masses. Also, earth homes blend in perfectly with the landscape and highlight the beauty of the surroundings, which is a significant basis of the [[arcology]] concept. For example, [[yaodong]] and pit cave dwellings in Northern China hide themselves underground and blend in perfectly within the Loess plateau environment. [[Salt Cathedral]] in a halite mountain near the city of Zipaquirá, Colombia hugs the contour and highlights the natural features.

===Disadvantages===
====Financial cost====
Three main factors influence overall cost of home construction, namely, design complexity, materials used, and whether the owner(s) carries out some or all of the construction or pays others to do it.<ref name="mcconkey2011" /> Custom houses with complex designs tend to be more expensive and take longer to build than stock houses. Houses which use expensive materials will be more expensive than houses which use low cost materials. Owner labor can dramatically cut construction costs.<ref name="mcconkey2011" />

Both earth sheltered projects and construction of regular houses have significant variability in the design, materials and labor involved. As such it is difficult to make a precise comparison of cost between the two, however in general an earth shelter is much more expensive.<ref name="mcconkey2011" />

A small "underground home" built in the style of Oehler, as only a simple, non-waterproofed hole in ground with simple planks and a plastic sheet to a wall, despite using free labour (ignoring the [[opportunity cost]]s of not having time to go to work) and recycled materials, e.g. windows and planks for the wall, is estimated to be 30% cheaper to construct when compared to paying a contractor to build a regular house using new construction materials at standard prices,<ref name="mcconkey2011" /> although Oehler's design will quickly rot and collapse after a few years.

A particular factor that strongly influences the cost of an earth shelter is the amount of earth that covers it. The more earth covering the structure, the greater the expense is needed in having a structure capable of withstanding the load (see also: [[#Roof|Roof]]).<ref name="roy2006" /><ref name="mcconkey2011" /> Another important cost factor that tends to be unique to earth shelters is site excavation and backfilling.<ref name="roy2006" /> The amount of waterproofing is also more costly. On the other hand, earth shelters should have lower maintenance costs since they are mostly covered with little exposed exterior.<ref name="reddy2003" />

Many financial institutions outright exclude financing on earth-sheltered homes,<ref name="wampler2003">{{cite book |author1=L Wampler |title=Underground homes |date=2003 |publisher=Pelican Pub. Co. |isbn=9780882892733 |language=en|oclc=58835250 }}</ref> or require this type of property to be common for the area.{{citation needed|date=January 2019}}

====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]]).<ref name=thorpe2018>{{cite book |author1=D Thorpe |title=Passive solar architecture pocket reference |date=2018 |publisher=Routledge |isbn=9781138501287 |language=en|oclc=1032285568 }}</ref> 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 (fungus)|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&nbsp;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.<ref name=roy2006>{{cite book |last1=Roy |first1=Robert L |title=Earth-sheltered houses: how to build an affordable underground home |date=2006 |publisher=New Society |isbn=9780865715219 |language=en|oclc=959772584 }}</ref>

====Limited escape routes====
Compared to above ground house, earth-shelters may have limited escape routes in case of emergency,<ref name="reddy2003" /> which can fail egress and fenestration building codes.<ref name="roy2006" />

====Legal issues====
An earth shelter may not be able to be adapted to existing local building codes, and may not legally be lived in.