GRAĐEVINA EARTH-SHELTERED HOUSING BUILDINGS IN THE ENERGY EFFICIENT STRUCTURES CONTEXT

Razvoj podzemne stambene arhitekture u velikoj meri zavisi od okruženja u kojem su objekti bili izgrađeni (klima, geografsko područje...) ali i od materijala i tehnologije koji su primenjeni prilikom građenja. Većina podzemnih stambenih objekta podignuta je u područjima u kojima su visoka temperatura i retke kiše klimatske karakteristike, a retko su prisutni u hladnijim, planinskim krajevima sa snegom. Istraživanja pokazuju da je podzemno stanovanje veoma zastupljeno u mediteranskim zemljama, Aziji i Africi, Severnoj Americi i delovima Evrope, i to u većem ili manjem obimu u svim istorijskim periodima. Od praistorije do danas, čovek se prilagođava uslovima i okruženju u kojem obitava, postepeno podižući nivo kvaliteta življenja i funkcije zajednice u kojoj učestvuje kao jedinka. Pećine, planine i pustinjski ambijent nude mogućnosti za različite oblike podzemnih habitata. Od čovekovog napuštanja pećine, on se bori s problemima da savlada prirodu i bira najfunkcionalnije i najprikladnije oblike fizičke strukture da bi zadovoljio svoje potrebe. Podzemni objekti, kao specifičan oblik građevine koja zadovoljava potrebe stanovanja, pojavljuju se na svim delovima naše planete.[1] Njihova tipologija uglavnom najviše zavisi od klimatskih karakteristika područja na kojem čovek živi. [2] Podzemni stambeni objekti suštinski se mogu istraživati putem njihove dve najčešće pojave:


INTRODUCTION
Evolution of underground residential architecture is largely dependent on the environment in which the buildings were constructed (climate, geographical area ...), but also of the materials and technologies used during the construction.Most residential underground facilities were built in areas where the climatic characteristics are high heat and rare rainfall, while they are rarely present in colder, mountainous areas with snow.Researches indicate that the underground dwellings were built in many Mediterranean countries, Asia and Africa, North America and Europe, with a greater or lesser extent, through all historical periods.
From prehistory to nowadays, man adapts to the conditions and environment in which he resides, gradually raising the quality of life and the function of the community he acts as an individual.Caves, mountains, and desert ambients offered opportunities for different forms of underground habitats.From the man's exodus from the cave, he is struggling with the problems of overcoming nature and choosing the most functional and most suitable form of physical structure for the fulfillment of his own needs.Underground objects as a specific form of structure for meeting the needs of housing, appear in all parts of our planet.[1] Their typology was mostly dependent on the climatic characteristics of the climate that man lived.[2] Earth-sheltered housing objects can essentially be viewed through their two most commonly occurring forms; Dr Aleksandar Rudnik Milanovic, architect and urban planner, Directorate for Urban Planning, Kragujevac, aleksandarrudnik@gmail.com Dr Nadja Kurtovic-Folic, professor, University of Novi Sad, Trg D. Obradovića, 21000 Novi Sad, nfolic@uns.ac.rs  podzemni stambeni objekti smešteni u prirodnom okruženju s minimalnom intervencijom ljudi;  podzemni stambeni objekti koje ljudi stvaraju, menjajući karakterisitike prirodnog okruženja pri čemu nove strukture prilagođavaju prirodnom okruženju.
U Americi se istraživanje o energetskoj efikasnosti podzemnih stambenih objekata sprovodi od osamdesetih godina prošlog veka.Parametri koji konkretno ukazuju na potrebu da se definišu propisi za izgradnju ovih objekata, na osnovu činjenica koje su merljive, potvrđuju da podzemni stanovi predstavljaju kuće s vrlo  Underground residential buildings located in a natural environment with minimal human intervention;  underground residential buildings that man creates by changing the characteristics of the natural environment and the new structure adapts to the natural environment.
Unlike a prehistoric man, a man of the 21st century has far greater technological abilities to compare life in underground facilities to his needs, whether it is one or the other mentioned approach to the use of these facilities.[3] Underground structures represent a combined sustainable model, which functions primarily on the recycling of atmospheric waters from the surface of green roofs, using energy derived from earth or groundwater for heating and cooling purposes.Due to limited spatial capabilities in cities for the application of bioclimatic design principles, by affirming the development of subterranean buildings outside settlements that are not infrastructural supplied, it is possible to achieve maximum energy efficiency by introducing solar systems as the third supplementary form of energy supply.The direct result of applying the model of underground facilities in urbanized environments is to maintain the total area of the soil under vegetation, thus achieving the maximum effect of achieving favourable impacts on the quality and the quantity of ecosystems that can be preserved using this form of specific construction type.[4] Evolving from the caves and other different types, over 50 million people live today in earth-sheltered housing.New underground residential architecture is created with great awareness for increased energy consumption and built on the experiences of anonymous builders of underground facilities, whose concepts today are innovative solutions to the problems of a man of the 21st century.[5] In this article, we suggest significantly more favourable energy aspects if underground structures becomes more common.

EARTH-SHELTERED HOUSING BUILDINGS IN THE ENERGY EFFICIENT STRUCTURES CONTEXT
Special attention during the construction of underground residential facilities with the aim of reducing the impact of atmospheric precipitation should be paid to:  Selection of the site for construction  Making drainage in accordance with the location and terrain waterproofing layers in all aspects of contact with the ground facility.
The vegetation on the site for construction can have multiple benefits for future operation of the facility.Green Fund can be viewed from several aspects in terms of its impact on the underground dwellings.One, of course, is a significant energy saving that can be achieved with the existence or planting trees at the site planned for the construction of an underground dwelling.The tests related to the amount of energy saving with green plantations are not yet done, but it is known from practice that the plantations on the southern front of the underground residential building can significantly reduce the temperature inside the building in summer.
ground residential facilities is conducted since the 80th of the last century.Parameters that specifically point to the need to define regulations for the construction of these facilities, based on the facts that are measurable, and which indicate that the underground dwellings are houses with very good energy performance.Research on energy efficiency; primarily implies to determine the parameters which lead to the assessment of the benefits of building underground in relation to the above-ground structures.The same results could be obtained in reducing CO 2 emissions by using more energy-efficient models such as underground structures.[6] According to the database compiled during the mentioned research "it can be said that the houses covered with earth exhibited considerably better energy performances than the standard surface houses".The claim that the energy consumption for this type of houses can be reduced up to 75%, can be proved using the data related to monitoring the thermal integrity factor parameter, which in case of the houses covered with soil averages 28.40 KW/m 2 daily, while the same parameter in case of traditional surface houses averages 113.56 KW/m 2 ". [7] On the event of the research conducted on two south-oriented structures: one being earth-sheltered elevated housing and the standard surface house of the same area the Staniec and Nowak from the Department of Civil Engineering at the University of Technology of Wroclaw, concluded that the losses and gains stand in certain proportions, with very similar indicators.They also determined that if value parameters for cooling and heating are separately analyzed, considerable differences are observed.[8] They found that they arise due to the fact that the thermal loss in an earth-sheltered housing is considerably less than in the surface housing, but only during the heating season and that during the summer season, thermal loss in the earth-sheltered housing is higher.Since the temperature of soil in the summer is lower than the air temperature, this causes cooling of the structure.it is one of the main reasons why underground structures require considerably less energy than the surface ones.They also noticed that during the heating season "thermal losses in underground residential buildings by 14%, 8%, and 5% are less by the 5cm, 10cm and 20cm thickness of thermal insulation.Increasing the thickness of the layers of the earth above the roof panel reduces heat losses by 20-25%, 10-15% and 5% for 5cm, 10cm and 20cm thermal insulation compared to 0.5m thermal insulation".The [9] in this sense, it can be concluded that heat gains in the underground housing structures are up to 40% higher than in the surface structures.
In order to show the theses from their research with clear comparative relationships of average values Stanjec and Novak developed a "heat loss diagram" which represents a comparative analysis of the aboveground and underground objects, depending on the thickness of the insulation and the thickness of the ground layers in underground objects, presented as average values, values during the heating season and the cooling season.
The research conducted by Oklahoma State University [10], and Wendt [7] confirm underground residential buildings as energy-efficient buildings and were of great importance for the relationship to the assessment of the energy efficiency as one of the most important components of general efficiency of underground buildings.
When the statistics such as this is viewed in the light of qualitative initial reasons for the change of an entire set of documents related to planning and construction areas, one can expect promotion of a more widely present underground housing architecture, with one of the primary goals of the present times, which is planning and construction of individual buildings, but also of entire settlements, where this housing typology can be implemented with an aim of creation of future energy efficient settlements in the Republic of Serbia.[11] [12]

IMPACT OF BIODIVERSITY ON EARTH-SHELTERED HOUSING
The presence of vegetation at the construction site can provide multiple benefits for the future functioning of the structure.[13] The greenery can be observed from several viewpoints, regarding its impact on the earthsheltered housing buildings.One certainly important aspect is energy saving which can be achieved by having or planting trees on the location planned for construction of earth-sheltered housing building.The tests related to the amount of energy saved by planting the greenery have not been conducted yet, but it is known from the practice that plants on the south side of the earth-sheltered building can provide the significant reduction of the temperature inside the building in the summer season.(after [14]) Ako se sade nove biljke, potrebno je da se na južnoj strani objekta zasade listopadne biljke, kako bi se omogućilo prodiranje sunčeve svetlosti kroz ogoljene krune drveća u zimskom periodu.Vetar, takođe, može If new plants are planted, it is necessary to plant deciduous trees on the south side of the structure, so as to allow sunlight penetration through bare tree crowns in winter.The wind can also impact the building tempera-uticati na temperaturu zgrade, tako da se, u zavisnosti od smera duvanja vetra, može saditi nova vegetacija ili se može koristiti postojeća, sprečavajući tako direktan udar vetra na objekat.
Uticaj atmosferskih padavina na podzemnu stambenu arhitekturu jeste jedan od najvećih rizika za njihovu eksploataciju.Tipologija podzemnih objekata predstavlja mogućnost za manje ili veće uticaje atmosferskih voda.Prema Reju Skotu, autoru knjige "Kako izgraditi svoj podzemni objekat" (How to build your own underground home) najveću opasnost po podzemne objekte predstavljaju ukopani objekti, jer ovaj tip objekata omogućava pojavu nekontrolisane količine vode pri obilnim padavinama.[16] [17] ture, so depending on the wind blowing direction, vegetation can be planted or the existing vegetation can be used, preventing direct impact of the wind on the structure In the report of the Agency for Energy of Minnesota, related to the research in South Dakota, it is stated that "when comparing the parameters for two identical objects (one with greenery in the immediate environment and the other without greenery), the following conclusions were reached:  House that had greenery in the immediate surroundings of the building, had savings of up to 40% energy in relation to a house without greenery".[15] That research also indicated that there is an impact of the vegetation on the saving in the usage of earthsheltered housing so that when constructing such structures, it is necessary to plan the vegetation in accordance with the building orientation and local requirements.

Impact of rainfall on underground housing
When constructing underground housing, a special attention must be paid to:  The choice of location of construction of the structure  Construction of a drainage system, regarding the location and land configuration  Construction of waterproofing layers at the contact of the structure with soil In order to reduce the rainfall impacts.
The impact of rainfall on an underground housing structure is one of the greatest risks for the operation of such buildings.The typology of underground structures represents the potential for a weak and the strong impact of rainfall.According to Ray G. Scott, author of the book "How to build your own underground home" "The greatest danger to underground objects is buried objects because this type of objects allows the appearance of uncontrolled water in abundant precipitation".[16] [17]
Poseban problem koji prouzrokuje potencijalnu štetu zbog pritiska kiše koji prolazi kroz slojeve zemlje do objekta javlja se u podzemnim zgradama u onim slučajevima kada nema kanalizacionih kanala i mrežnog sistema s drenažnim cevima, kojima bi se odvodila voda nakupljena na zidu prema nagibu.[18] Pored rizika od bočnih uliva atmosferske vode, osnovni problem koji su podzemni objekti imali s velikom količinom vode i vlage u objektu, nastajao bi kada bi se, pri projektovanju, odabrao pogrešan tip objekta u odnosu na teren.Jedan od takvih primera upravo je objekat atrijumske ukopane kuće u Arizoni, građene osamdesetih godina prošlog veka.Prema izjavama samih vlasnika, objekat je u najvećem broju slučajeva imao probleme s nekontrolisanim prodorom atmosferske vode, usled položaja pristupa objektu, koji se odvija preko atrijuma, formiranog ispod saobraćajnice, i to na nižoj koti u odnosu na put s kojeg se pristupa objektu.[19] A particular problem causing potential damage due to the rainfall pressure flowing to the house through the earth layers is found in elevationin-hill underground buildings, in those cases when no drainage canals and drainage pipe network system is provided, which would drain the water accumulated on the wall towards the slope.[18] Apart from the risk form the lateral penetration of rainfall, the basic problem the earth sheltered buildings had in terms of excess water and dampness in the structure was caused by the improper choice of structure for the land configuration in the design phase.[One of such examples is the atrium envelope house in Arizona, built in the 80's of the previous century.According to the owners themselves, the building in most of the case had a problem with the uncontrolled penetration of rainfall, which is caused by the position of the access to the house, which is organized via an atrium created below a road, at a lower level than the road used for accessing the house.[19] Slika 4. Podzemna kuća sa atrijumom u Arizoni: a. pozicija pristupa objektu; b. pogled na objekat ukopanog tipa sa atrijumom (prema [19]) Pojava privremenih podzemnih voda pri prelasku iz jednog u drugo godišnje doba, "može stvoriti problem usled velikog nagomilavanja vode u situacijama kada je nepripremljen objekat izložen pritisku vode" [20], koji se može znatno smanjiti preduzimanjem svih potrebnih koraka prilikom same izgradnje objekta.
The occurrence of temporary underground waters when the season's change, "can create a problem due to the large accumulation of water in situations where the unprepared object is exposed to water pressure" [20], which can be significantly reduced when all necessary steps when constructing the building are taken.
By creating a drainage layer made of sand and gravel and by placing a drainage pipe around the building potential for damage to the structure and penetration of rainfall water is considerably reduced.
In addition to the standard approaches to the building of waterproofing layers of the underground structures roofs, the negative impacts can be considerably reduced nowadays by installing rubber membranes, which not only prevent water from penetrating the structure but retain water so that vegetation system above the roof structure can use it.
A survey of the geological layers of earth, along with information on the stability and layers of ground waters can prevent potential negative situations during the building service life.
Research of energy efficiency, comprise the primarily identification of parameters used to assess advantages of construction of earth sheltered structures over the surface structure, but also of buried structures in comparison with envelope/true underground structures.Depending on the input parameters and characteristics of researched structures, different results can be obtained.Yet, it is interesting to point out that the obtained data are exact and computational, obtained using specialized software.In addition to data about thermal conductivity, energy efficiency depends on a number of other factors, which cumulatively affect the assessment of energy category of an underground housing building as could be seen in Table 1.Istraživanja termalnih pokazatelja, obavljena na nasutoj podzemnoj stambenoj kući u Misuriju, predstavljaju "parametre praćenja temperature u tom objektu u periodu od četiri dana sa intervalima merenja od šest sati, prilikom kojih je uočena konstantna unutrašnja temperatura, u odnosu na promene spoljne temperature".[21] Ti podaci konkretno ukazuju na prednosti izgradnje podzemnog nasutog stambenog objekta, posebno uzimajući u obzir činjenicu da za održavanje konstatne temperature prilikom merenja nisu postojali niti su korišćeni sistemi za zagrevanje objekta.
Statistički podaci ukazuju na konkretne pokazatelje, prema kojima u gradu danas živi više ljudi, nego u njegovom okruženju ili samoj prirodi.Poslednjih sto godina zabeležen je protok stanovništva i migracija sa imanja na sela, od sela ka gradovima i od gradova ka metropolama.Poznato je da gradovi koriste do 75 posto globalnih izvora energije i proizvode većinu otpadnih materijala.[24] S takvom stopom potrošnje energije, The research of thermal indicators, conducted on the bermed earth sheltered house in Missouri represent "parameters for monitoring the temperature of this object for a period of 4 days with 6-hour measurement intervals, during which a constant internal temperature is detected, in relation to the changes in the outdoor temperature".[21] Those data indicate advantages of construction of bermed housing buildings, especially taking into consideration the fact that for retaining of constant temperature during measuring, no building heating systems were used.

Earth sheltered housing buildings in the context of reduction of negative environmental impacts
Since 1900 and the French architect Eugene Hénard [21], who had a manifest advocating the system of underground traffic at several levels, through Frank Lloyd Wright who in 1930 established a system of peripheral cities [22], up to the present day cities with towers, as a characteristic typology of tall building of 21 st century we have come to the point of community development where the necessity to reduce negative environmental impacts, through the model of return to nature and life outside polluted urban central zone, can most likely be effected by a direct interaction with natural environment.[23] Underground housing structures in this context can be considered as structural mediators in the epicenter of such interactions.
The statistics indicate concrete data, according to which there are more people nowadays living in the cities, then in their environment, or in nature.In the last one hundred years, the flow of population and migration from the countryside towards villages, and from the villages towards cities and from the cities towards metropolises was recorded.It is known that cities use up to 75 per cent of global energy resources and produce gradovi postaju generatori negativnog uticaja globalnog zagrevanja na planetu Zemlju.
"Observing statistics that point to the fact that commercial and residential objects in CO 2 emissions in the atmosphere account for 39 percent, and that in almost 70% of cases these consumers are consumers of electricity (taking an example of analysis conducted in the US), it is clear that the use of energy for cooling and heating are of key importance for the environmental impacts that objects perform in their environment."[25] In order to compare heating energy costs incurred by an average surface and an underground housing building, a case study for the building of 135m 2 was made.This study confirmed that underground housing architecture can result in the reduction of 72% of energy consumption in comparison with a standard surface house.Posmatrajući ove podatke, može se zaključiti da je potrošnja energije podzemnog objekta u letnjem periodu za trećinu niža od one za nadzemnu zgradu, dok je potrošnja energije tokom leta nula, što znači veoma mnogo u smislu zaštite životne sredine, jer su uticaji znatno smanjeni.[26] U slučajevima kada su korišćene druge vrste energije za grejanje, kao što su gas ili ulje, može se primetiti da su korišteni tri do četiri puta manje, tako da se ukupna količina energije tokom zime može smatrati finansijskom uštedom, ali predstavlja i ekološki prihvatljiv metod, u pogledu ukupnog uticaja na životnu sredinu.Mogućnost formiranja veštačkih zelenih krovova primenjiva je za obe tipološke grupe stambenih zgrada, tako da se kontekst ekološki prihvatljivog oblika zgrade može pozitivno posmatrati i na ovaj način, uzimajući u obzir činjenicu da zelena krovna struktura utiče na povećanje površine ispod vegetacije ili zadržavanje postojeće vegetacije u građevinskoj zoni.
Svi tipološki oblici arhitekture podzemne stambene kuće do sada su bili uglavnom pojedinačni, eksperimentalni napori.Nisu postojali, takođe, ni propisi za efikasan nadzor nad izgradnjom ovih objekata.Za srpsku teoriju i praksu međunarodno iskustvo je od ključnog značaja za dalji razvoj i usklađivanje s proce-By observing these data, it can be concluded that the energy consumption in the summer period is for third lower than that of a surface housing building, while the energy consumption in the summer is zero, which means a lot in environmental terms, as impacts are considerably reduced.[26] In cases where other kinds of heating energy were used, such as gas or oil, it can be noticed that they were used 3 to 4 times less, so the total amount of energy during winter can be considered financial saving but also the environmentally acceptable method, regarding the total environmental impact.The potential for formation of artificial green roofs is a possibility of both typological groups of housing buildings, so the context of environmentally acceptable form of buildings can be positively observed separately, taking into account the fact that he green roof structure affects the increase of area under vegetation or retention of the existing vegetation in the construction zone.

CONCLUDING REMARKS
Underground housing architecture represents an energy efficient type of structures.This specific type of housing construction is recommended for the standard surface buildings because of its more energy efficient properties and its quality.
Zahvalnost: U članku je predstavljen deo istraživanja koja se obavljaju u okviru projekta TR36042, a koji finansira Ministarstvo prosvete, nauke i tehnološkog razvoja Republike Srbije.development and harmonization with procedures during designing and construction of underground housing structures for the following reasons:  In almost all presented examples, the underground construction approach indicated considerable savings accomplished by such construction models;  Combining of green roofs with the bermed elevation structures is the most common construction model in Serbia;  Construction of these structures is to a great extent present in Vojvodina, which already has a tradition of construction of such buildings;  Average temperatures in underground housing buildings range between 16 -20 degrees Celsius;  Green roofs, with medium requirements, semiintensive, are assessed as the type which can provide good effects during the entire summer [27] [28] so this type of the green roof can be observed as an adequate for bermed underground housing;.
 Maximum savings are accomplished with a green layer of the roof garden, where the soil layer is from 100 to 900 mm thick; -the optimal type of roof garden has bush vegetations -300 mm thick layer of soil with shrubbery can save up to 15% of yearly energy consumption, that is, 79% saving of building cooling energy;  Roof gardens reduce the heat flux for 52-57% in comparison to ceramic or metal roofs.[29] [30] In order to maintain constant temperature during winter period, it is necessary to design alternative hybrid systems for supplying structures with the necessary amount of energy, as a combination of wind power generators and solar panels; The advantages of implementation of underground housing architecture are the reduction of heat islands effects and saving energy in buildings (underground housing buildings reduce yearly heating and cooling energy demands), [31].On the other hand, regarding the fact that solar radiation has considerably higher intensity in the summer, underground housing buildings play an important role in the reduction of the cooling energy consumption in comparison to the standard surface thermally insulated buildings.[32] On the basis of the described research, the recommendations for the design of the bermed elevation type buildings can be formulated.This recommendation should be related to the proper choice of the used materials and construction techniques, which generate the results which are implemented on the assessment of new designs which enrich typology of underground housing structures.
The conducted research prove that underground housing structures represent an adequate and very good quality housing model which is very adaptable and can be implemented across the entire territory of the Republic of Serbia.

RUDNIK MILANOVIC Nadja KURTOVIC FOLIC
Underground housing architecture represents an energy efficient type of structures.This specific type of housing construction is recommended for the standard surface buildings because of its more energy efficient properties and its quality.
All the typological forms of underground housing architecture up to date were mostly individual, experimental endeavors.Construction had no regulations for efficient monitoring of construction of these structures.For Serbian theory and practice international experience reviewed in the article is crucial for further development and harmonization with procedures during designing and construction of underground housing structures.
When the international experience is viewed in the light of qualitative initial reasons for the change of an entire set of documents related to planning and construction areas, one can expect promotion of a more widely present underground housing architecture, with one of the primary goals of the present times, which is planning and construction of individual buildings, but also of entire settlements, where this housing typology can be implemented with an aim of creation of future energy efficient settlements in the Republic of Serbia.

Slika 2 .Figure 2 .
Figure 2. Examples of biodiversity impacts on the earth sheltered buildings: a. vegetation blocks solar radiation in summer season; b. vegetation lets through solar radiation in the winter season; c. vegetation as a protection from wind.(after[14])

Figure 4 .
Figure 4.The atrium envelope house in Arizona: a. Building access position, b.View of the envelope/true underground building (after [19]) pritisak na zidove objekta water pressure on the wallsSlika 5

Table 1 .
Degree of efficiency regarding the structure typology

Table 2 .
Ratio of energy consumption, standard surface house in comparison with underground structures