EARTH SHELTERED COMMUNITIES :
IN AN ARID HIGH PLAINS ENVIRONMENT
This thesis is submitted by Barbara Figlio
as partial fulfillment of the requirements for a Master of Landscape Architecture Degree at the
University of Colorado at Denver College of Design and Planning Graduate Program of Landscape Architecture
"We are slowly inclining to the Indian belief that nature is not inanimate, but imbued with one common life-force: the living water and living earth, the mountains, trees, plants, animals, and man. All are born of Mother Earth, all are bound together in unbroken continuity, in an indivisible unity of both biological and spiritual ecology."
wilderness 1. an uncultivated, uninhabited region; waste; wild. 2. any barren empty or open area, as of ocean.
3. a large confused mass or bewildering collection.
In the last two hundred years we have been erasing the wilderness. Viewing it as an uninhabited waste or barren area, we have used the wilderness as a raw material with which we have created our civilized communities. With increasing standardization, the spread of these communities has prompted the disappearance of our forest, prairies, and a rich diversity of other natural cultures. In their place, our communities ironically exhibit a similar look and feeling of a vast region of bewilderment.
It is no coincidence that our original view of the wilderness has led to this circular outcome. For the wilderness is not a physical state, not a region of waste; rather it is a community in itself. It is a community which boundaries include soils, water, air, plants, animals and the cycles of energy. It is a finely balanced orgainism, self reliant in nature and cleanly compatible with the future.
If we are to have a long term existence, a future, we must begin to see this aspect of wilderness. Reassessing and reevaluating our facts, attitudes and beliefs can give us the insights necessary to achieve a greater sense of community in our lives.
Being blind to the sense of community in nature has resulted in being blind to the nature of community. We must continue to learn the lessons of the wilderness, of the land, and emulate these lessons in order to create an harmonic niche for ourselves in the greater community of this planet.
"The only way I could live in perfect harmony with the natural world would be to throw away my credit cards, my clothes, my toothbrush, my Blue Cross, my vitamins, my house, my car-everything- and walk off into the bush, naked, ready to win or lose on my cunning alone.
With luck, I might last as long as two days, so I've got to find another way to live successfully, and thats what architecture should be all about: trying to find alternative ways of life, compatible with the right way, the naked in the wilderness way.
If we still had a wild instinct, we might find them a lot faster, but we traded that instinct for a brain, and so must think our way along step by step."
This paper then, is a step in a long process of thinking a way back to nature, back to the earth.
Purpose and Goals 2
THE EARTH SHELTER TYPOLOGY 8
The Concept 9
The Form 11
Form and Energy 13
Form and Sociability 16
SITE CRITERIA 20
COMMUNITY PLANNING 29
Lot Sizes 30
THE PRINCIPLES 38
THE CASE STUDY 40
Site Considerations 44
Development Suitability 60
Development Concept g3
The Site Plan g7
The central subject of this study is the development of an earth sheltered community and the design considerations within this community,, The need to research this topic is a response to significant changes which have occurred in recent years. Increasing costs of energy and decreasing natural resources have become serious problems causing reevaluation of our practices and life styles. In addition, some past development patterns have not produced the desired characteristics which lead to quality communities, while seriously jeopardizing the natural environment.
Energy consumption is increasing exponentially, while conventional sources such as oil, coal and natural gas are reaching their limitations. Production of nuclear power has been controversial and prohibitively expensive. It has been noted that the United States devotes over one-third of all of its energy to buildings and about one-quarter more in transportation. Thus well over half of the energy use in the nation is determined by our land use habits. These habits have been codified in land use and building construction policies and laws. Since prominent studies have concluded that energy conservation or reduced consumption is the most cost effective method of dealing with the energy supply problem, we must reevaluate these policies and laws to bring about necessary changes. In addition to decreas-
ing energy use within housing units, the entire land development process offers many opportunities for practiced conservation in over all land use, roads, u-tilities, transportation patterns, and construction methods.
Although the energy problem is a dominant issue, an increasing concern for the natural systems has surfaced. As we deplete natural resources and systems are stressed to capacities, we are forced to look for new attitudes and methods of management toward the environment. These new questions and concerns as with the energy problem must be incorporated into our land development processes. Development strategies that promote conservation of open space, vegetation, and water appear not only to present fewer environmental risks, but to be the most cost effective long term alternatives.
The energy supply and environmental quality problems clearly form the basis for new gols that must be met and incorporated in the development process. These goals, however, must be combined with providing a quality community responsive to inhabitants. Past development patterns have not necessarily met this concept. In seeking solutions to reducing energy consumption and protecting the environment, this third goal must not be overlooked.
According to the Front Range Project Committee, housing is expected to double on the Front Range within the next twenty
years. Competition for land use, stress on natural systems, demand for greater energy supplies are some of the problems that prompted the committee's decision to look for new goals and alternatives.
PURPOSE AND GOALS
It is the assumption of this study that the energy and environmental features and extremely favorable life cycle costs of earth shelter buildings are in harmony with these goals. The purpose of this study is to explore the nature of the earth sheltered dwelling and define potentials and design considerations necessary to utilize this new building type in community form. With this purpose in mind, the goals that guided this study were:
to define the nature of the earth sheltered dwelling
to establish principles which would facilitate the adaptation of this form to the arid high plains
to establish principles which would facilitate community scale design
to develope concepts of design utilizing these principles
to apply and illustrate the use of this information in a case study
to design an energy efficient community of earth sheltered dwellings compatible with environmental, social and aesthic needs
The approach to this study also serves as a road map for the document. Since the alternative of earth shelter dwellings and communities has not widely been used, the research portion of this study was extensive. An historic overview was first conducted to shed more light on the concept of earth shelter. This concept was then looked at in greater detail to define the form giving properties which result from physical, social and regional interaction. The combination of these factors reveal then a new building typology for the arid high plains.
In order to create earth sheltered communities, the nature of existing communities and the interaction of a new typology was explored. The results of this research is a new synthesis of meaning. It is expressed in a set of principles or guidelines which govern earth shelter design within this region.
The next phase of the study was the case study design. A prototypical site was chosen to illustrate the issues and principles discussed previously. A methodology, combining traditional and new techinques, was choseri to inventory and analyze the design resources of the site. Once revealed, design resources and principles were integrated to develope conceptual designs.
Overall evaluations and comments then concluded this study.
SYNTHESIS THE PRINCIPLES
THE SITE INVENTORY
site features SUITABILITY ANALYSIS DESIGN CONCEPT THE DESIGN
Using the earth as shelter is not a new concept. Although this concept invokes images of prehistoric men finding shelter in natural caves, the creation of underground and earth covered structures has persisted through the world among a variety of peoples.
As with any architectural solution, the underground alternative has been used to achieve a multiplicity of benefits. Reasons for developing historical communities were responses to availability of building materials, climate, defense, ceremonial intentions, nature conservation, and intensification of land use. The physical and social needs of people combined with the fundamental concept of shelter resulted in a variety of indigenous architecture suited to climate, place, and culture.
paraline section, Cappadocia community
As in Cappadocia, Turkey the combination of human antagonists and climatic pressures initiated the people to dig their communities into the existing natural formations of Tufa stone. The results was a highly defensive underground community which protected its inhabitants against hot summers and artic winters.
atrium dwellings Honan, China
Throughout Chinas loess belt in the provinces of Honan, Shansi, Shensi and Kansu, millions of inhabitants exploit the insulative qualities of the soil against the severe w'inter climate. By building subsurface atrium dwellings, these people not only achieved comfort and protection, but conserved the land above for farming and grazing. These farmers dug their homes and literally lived beneath their farms creating levels of multiple land use.
These reasons for developing terratect-ural communities in the past are not so different from those which interest us today. Past worries of climate are now expressed as energy conservation. The conservation of land and nature are now ecological concerns. Man by nature has always faced similar pressures and problems .
What then can be learned from historic examples of earth shelter? The historic earth shelters throughout the world have derived their forms through constraints imposed by the environmental and social situation within which they have originated. Similar to other architectural expressions, earth shelter design is a contextual statement. The context within which we seek future use of earth shelter must be fully examined.
Regional climate and thermal properties are not now clearly understood. To optimize our efforts, we must examine the range and opportunities these conditions.
In order to employ the concept of earth shelter to this region, designers will face the issues of social behavior and social acceptance. We must know more about the meaningful attributes of our already existing environment in order to integrate them with such a radically new concept.
Finally, history reveals earth shelter to be a time honored response to a variety of human purposes. The heritage of
underground development not only provides us a laboratory to examine lessons, successes and failures, it also promises great potentials.
THE EARTH SHELTER TYPOLOGY
Earth Shelter is a general term referring to structures that use a blanket of earth to moderate the effects of climate. The suitability of subterranean construction for various climates is dependent on many considerations. Subterranean structures do not effectively suit humid, warm climates due to the extensive ventilation necessary to achieve comfort and the po-tentional of high water tables. Yet in very hot and dry climates, such as the arid west, very cold and dry climates, such as central Canada and the temperate cold and snowy areas, such as Wisconsin and Maine, the underground alternative can be very effective.
Dr R. L. Lytton has suggested that the Thornwaite Index might serve as a guide to prime locations for earth covered buildings. This index relates climatic and geological characteristics of regions based on the surplus/deficiency of moisture. Dr. Lytton suggests that either a negative or small positive index number might indicate regions which offer conditions most favorable to earth covered buildings. These regions are areas of stressed climates defined by a great differentiation between daytime and nighttime temperatures and little or no precipitation.
The Arid High Plains of Colorado exhibits those characteristics of a stressed climate. Regional features are low humidity, abundant sunshine, light rainfall.
and moderate to high wind movements accompanied by a large range in daily temperatures. There is also a marked difference between summer and winter temperatures .
Winters are cold and stormy with alternating sunshine. Winter storms are intense but of short duration and track from north and northwest to south and southeast. Each winter has as many as ten cold spells which move across the area as major storms. In summer maximum temperatures can sometimes reach 100 degrees. However, these temperatures modified by low humidity and followed by cool nighttime temperatures are usually within the zone of comfort.
Yet only a small percentage of the year affords comfort without suppliment-al heating and cooling. This presents the people living in this stressed environment with serious problems. Conventional solutions have been high energy consumption. The concept of earth cover can provide unconventional solutions to the same problem.
A more detailed examination of the concept of earth shelter reveals that the earth acts as a moderator in two ways.
It provides protection from wind, thus reducing infiltration. Secondly, the surfaces of the structure are exposed to temperatures which fluctuate less widely than those above ground. In addition the mass of earth creates a seasonal time lag resulting in warmer winter temperatures and cooler summer temperatures .
In the High Plains area where soil temperatures average approximately 55 degrees, a thermal lag of around 3*5 months
is created. Thus, the harsh effect of winter reaches its peak in earth around mid-spring and the maximum slimmer heat accumulates around mid October. Capitalizing on these thermal characteristics, earth covered buildings radically reduce supplimental heating and cooling demands. Moreover, the size of the unit necessary to fulfill actual heating and cooling requirements is thereby reduced.
High Plains thermal lag
It is not difficult to see the economic advantage to the concept of earth shelter. Not only is the initial cost of heating and cooling units lower, but continued life cycle costs are greatly reduced. A prominent Olkahoma study compared monthly total energy usage (kwt/hr) of earth sheltered homes with
conventional above ground homes. This comparison clearly demonstrated the performance potential of the underground concept. In addition to the dramatic peak to valley reductions, the total annual energy usage of earth covered dwellings is substantially decreased by approximately ^0 percent.
monthly total energy usage in above ground homes and in earth shelter.
In our Arid High Plains area, the Colorado Public Service has indicated that the average house hold uses 14,56^ killiwatt hours per year to heat their homes. At a cost of .05 cents per kwt/hr this average house hold then spends con-servativily speaking $?28 for suppliment-al energy. A savings of kO/o, by use of earth cover, would save the average
household around $300 a year. This freed capital can be used to meet rising interest levels and monthly payments.
Reduction of energy consumption is, by no means, the only benefit of the earth shelter concept. The advantages of the underground alternative are numerous.
Yet, reduction of energy consumption is currently the major attraction of the earth shelter concept a concept of providing a microclimate which modifies the extreme macroclimate of the Arid High Plains environment.
The employment of the underground concept can result in a variety of designs. The relationship of the structure to the existing ground surface, the degree of submergence, and the amount of earth cover desired, are major variables which can be manipulated to produce this variety.
A simple taxonomy or general classification of earth sheltered types is revealed on closer examination of these variables .
Integration of a structure to the earth can be achieved in two ways. Submerging the building below existing grade yields a chambered version of earth sheltered structure. Constructing the building at grade and wrapping it with a blanket of earth produces what is known as the bermed version. This, of course is a simplified view of the relationship of
the structure to the ground surface. It should be noted that the range between these two alternatives offers an "up and down" latitude. This latitude affords a variety of solutions to design or site specific problems
With these two general classifications of bermed or chambered earth shelter, the degree of submergence or amount of earth covered desired creates several more variations.
The totally underground structure is encompassed by earth. This variation1 is usually employed to achieve isolation from undesired conditions. Scientific laboratories which wish to reduce noise and vibrations from the external environment are an example of such use. In most cases the totally underground structure is inappropiate for dwellings, and limited to industrial or commercial uses.
The second variation is the atrium structure. A central courtyard open to the sky, allows light and warmth to penetrate the rooms encircling it. This structure type offers complete enclosure as compared to the elevational structure, which exposes one facade to the outdoors. The elevational earth shelter offers a greater accomodation to slopes, views, and greater interaction between structure and outdoors.
Finally, when less earth cover and greater openness is desired, side wall penetration can be employed. This variation increases opportunities to take advantage of special view, greater access, and later expansion.
by William Morgan
This general classification presents some form options of the underground concept. Specific design and site considerations will lead to the most appropiate selection of these variations. The most widely used of these options, however, are the elev-ational and the atrium house. Consequently, they will be used to illustrate the ideas and principles of this study.
FORM AND ENERGY
The earth sheltered dwelling'interacts so closely with its setting that both the structure and its surrounding landscaped spaces combine to make up "the building". To be climatically responsive to a specific region, modifications or adaptations to both the general form and adjacent spaces are necessary. The Arid Hi'gh Plains of Colorado present a wide range of climatic variables to which "the building" should respond.
the etevational building
In the elevational house, the structural form is generally elongated and oriented to maximize or minimize solar gain. Solar gain can be achieved in the arid plains by orienting structures due south or eleven degrees to the southeast or to the southwest. To increase this gain, the elongated form is adapted to desirable surface to volume proportions. Rectangular structures with proportions of 1:1.3 or 1:2.4 provide optimal conditions to balance neat gain and heat loss within the enclosed structure. These ideal proportions mitigate winter conditions and serve to reduce the stressful effects of high summer temperatures.
Using adjacent spaces to control the surrounding environment can afford fur-^ ther manipulation of form. The ideal rectangle can be altered when adjacent spaces collect and store energy. Wrap-
ping the elevational house around a modified adjacent space integrates energy as a volume. Similar heat gain by volume an be achieved by courtyard design that normally is achieved by the plane of the south facing facade.
south facade collects energy
energy is collected by volumn
Adjacent spaces can also be used to fine tune the energy performance of the earth sheltered dwelling. The space above or roofscape is used to absorb and store solar radiation. Reducing winds across the roof space in winter by use of screens reduces heat loss.
The adjacent space which is at grade level of the elevational structure can, also by proper design, be used as a climate moderator. In addition to a thermal mass, it can act to seasonally decrease heat gain. Proper placement of overhangs>and vegetation reduce heat build up and utilize the flow of desired breezes. Since humidity in the High Plains region is quite low in summer months, transpiration of vegetation and evaporation from designed water features can increase comfort by modifying hot summer conditions.
The atrium design, as stated before, requires no particular orientation. It therefore, can be placed in landforms of any exposure. Still the south facing windows act as the exposed facade of the elev-ational house. The inner courtyard is used as a thermal mass to integrate energy as a volume but can be used to reflect radiation to windows of other exposures. The size of the atrium is derived to balance the necessary heat gain to the size of the structure.
atrium size influences solar gam
The adjacent spaces of the atrium house act as those of the elevational building. Complete enclosure of the adjacent space at grade level alters ventilation design yet the concepts remain the same.
overheads reduce heat gain in court
cooled by summer breezes
The degree of performance achieved by "the building" of both the elevation and atrium earth shelter is dependent on the degree and quality of information known of the region and site. Seasonal information provides a basis for overall design. Hour by hour data can lead to detailed design necessary to produce high performance on a daily level. For example, on days of cool mornings and hot afternoons which are typical of the arid plains region, the system can utilize the warmth of morning sun while afternoon comfort is gained by shading. Other daily variations can be modified, by this detailed leyel of design to achieve maximum comfort and function within the building system. In this way a performing landscape envelope acts as a microclimate moderator.
As seen, the combine function of structure and adjacent spaces should be built to respond to the arid plains condition.
In addition site specific conditions re-
quire careful consideration,, Topography, existing vegetation, water bodies, and surrounding land use can greatly influence the climate at the ground. Design which relates to regional climate and site specific conditions produce forms most responsive to climate and place..
FORM AND SOCIABILITY
The form of any architecture is not solely a product of the forces of energy. Each building performs social functions which are based on patterns of behavior and psychological attitudes of our culture. To be successful, the architectural form meets both of these functions.
The resident of an underground dwelling may initially have an feeling of dominance, since he is directly exposed to successful attempts to cope with the demands of the environment. Yet to maintain a state of well being the social spaces of "the building" must in a sense overcome the underground phobia while performing their functions.
The psychologically negative image of subterranean living, associated mainly with darkness or absence of natural light, imposes mandatory requirements on the designer to make the structure attractive. Basic requirements include plenty of sunshine and penetration of natural light as well as a direct view to the outside. Windows, greenhouses and clerestories can be used to provide adequate light
and the necessary stimulus of arousal, derived from the external environment. Solutions to this problem would vary from site to site. For instance, in high stress urban environments a limited amount of windows might serve to reduce the level of arousal to a more moderate state.
While a quiet country setting might require many windows to bring in views and outdoor stimulus to increase the state of arousal. Thus the building must be responsive to positive and negative outdoor conditions.
Since the elevational house is outward oriented while the atrium is inward oriented, visual site condition may effect form selection or modification. Both housing forms may have berm penetrations to accomodate views. Berm forms may also be used to screen unwanted visual stimulus.
Another important design consideration of the earth covered house 'is the entry. Since the entry of the house is the first initiation to the underground dwelling, its psychological impact is of prime importance. Careful design can alter the underground bias. People should enter at the same level of the first floor or ascend to it. Since the earth sheltered house is usually located on a slope, this is easy to accomplish. In addition, the entry should delightful. The use of natural and artificial lighting, color, and plants can enhance the overall design.
Typically the elevational house is entered through the single exposed facade.
Entering through the exposed south side provides comfort and protection from winds Yet, having a public entry on the same side as the outdoor privacy space many not be desirable. In that case the entry may be created through one of the bermed sides of the dwelling.
Entry placement in the atrium design must reflect similar conditions. Entry can be down into the enclosed courtyard, or built into the berm to keep the courtyard private. Allowing more than one courtyard provides another alternative. Here the form changes to retain the private outdoor space, while entry through an additional open court occurs. Thirdly, the main courtyard can be open to the surrounding landspace when orientation and slope allow.
Placement of entries in both forms is further dependent on functional relationships between the garage and the relationship of the house to the street. Houses built on the north side of a street, may have a reduced sense of privacy and less yard space if auto access, entry, garage, and privacy space occupy the same side. Houses on the south side of the street do not face this problem since auto access is to the north of the dwelling.
The relationship of entry, auto access should protect the privacy of the occupants in both cases. Of course, road layouts which allow auto access to the side of the dwelling would be most desirable; but when this is not feasible, it is up to the designer to integrate these functions in a social and aesthetic way.
The adjacent outdoor spaces of "the building" also have soical and psychological considerations. With the house integrated, often the outdoor spaces are the only visible form or configurations conveying the houses image. For the residents they are the only immediate open spaces available. Design of this landscaped envelope must be thoughtfully determined.
The presence of soil on tops of buildings increases the potential for landscape. Scenic gardens on top of homes where a roof would otherwise be jutting out above ground should have positive effects. The visual impact of scenery may enhance feelings of pleasure. So too, the availability of gardens, or areas of cultivation may increase the sociability of the house.
Yet, features associated with the conventional house, such as trash storage, chimneys, spaces for solar collectors, fences, etc, must also be integrated into subterranean design. Due to the "hidden house effect" it is crucial to achieve this integration without creating a negative image. The combination of subterranean, semisubterranean and above ground levels within the design of the structure can ease the integration of such features. However, these elements cannot be left to be treated after house construction, rather they sould be carefully planned at a early design stage.
This discussion of how the social functions and psychological implications effect design thought and form is by no means complete. It serves to briefly explore some of the problems associated with a radically new concept. In summary, psychological problems may be overcome by producing opposite effects to the underground bias and by adding features to the environment which produce desirable emotional feelings. Since outdoor and enclosed space create "the building',' social and functional design
of spaces must take place at an early stage to achieve an integrated habitat. These considerations combine to shape the social form of the earth sheltered dwelling.
The process of site selection is a critical stage in the development of the subterranean house or community. A muliple of factors which lead to site selection have an impact on social features as well as energy consumption. Each site gains its unique character from the nature of these factors and their interrelation to each other. Therefore, it is necessary to study each factor and their relationship to the whole.
Of course, the site selection process is used for conventional development, yet the site factors present different considerations when based on the subterranean criteria. This section then, speaks to factors and criteria that serve as a guide to site selection.
Geological constraints must be taken seriously in selection of the site. It is unsuitable to build any structure, earth shelter as well as above ground, across active faults. Seismic movement in active faults can result in cracked structures. Yet, in fault areas that are inactive, it is safe to build some subterranean buildings.
It is not unreasonable to build earth sheltered buildings in other seismic zones where earthquakes occur. Underground structures afford greater safety than conventional ones in areas of this nature.
Seismic information on the High Plains and other areas of Colorado is currently being updated. This information reflects the fact that the future holds an increase in seismic movements for this area. The advantage of subterranean structures could be more meaningful to this aspect of the Colorado future.
The ideal geological formation in which to build earth sheltered structures is a sedimentary zone. Old marine deposits and river beds are sedimentary in nature. The High Plains of Colorado and the out-wash of the Rocky Mountains, the Colorado Piedmont, are formations of this type.
The ability to dig easily within this zone reduces initial costs and increases overall performance of building.
Rock formations, which line the Colorado Piedmont, and dot the High Plains can also be suitable. What one normally encounters in rock is "clastic mass". Clastic mass is essentially rocks that are pressed together with joints and fissures running in all directions. Excavation and bracing may be necessary in such formations; but techniques are available to render these areas desirable.
Areas which should be avoided when building earth sheltered structures are those that present subsidence problems. Subsidence may be critical to the underground construction. This is especially true where horizontal thrusts occur. On the Colorado High Plains this condition could occur in areas that are settling due to
the pumping of oil or water or to the mining of elements underground.
Most important in site selection is topography. Generally speaking, topographic configurations can be simplified into lowlands or flats, slopes, and hilltops. Each one of these configurations have design advantages and disadvantages. Considerations are based on both social and physical criteria.
Lowlands present certain limitations and potentials to earth shelter design. Limited views to the environment, possible drainage or flooding problems, the possibility of pumping sewerage and reduced ventilation or winds can be draw backs to flat areas. Major disadvantages to the lowlands are the large amounts of land required to integrate the structure, although chambered atrium design can somewhat reduce this requirement and accomodate a flat: area. Yet easy accessibility, construction and excavation offer some good opportunities.
On the other hand, slopes are the most desirable topography for earth shelter. Properly designed building on slopes can provide good views, light and capture heat and sunshine. Sewerage and drainage are improved by gravity conditions, and ventilation and heat gain are improved by elevation and land tilt.
Generally, slopes up to eight per cent are best for one story elevational or atrium design. Slopes 8 15 per cent are accomodated by one story elevational, and slopes 15 20 per cent are desirable for two or three story elevational structures. Slopes above 25 per cent require excessive modification and building technology at present time.
0-5% 5-8% 8J5% 15-25% 25
Two story O
The disadvantages of building on slopes is primarily in regard to accessibility. Access on slopes may require increased initial investments. Yet the development of slopes may be possible with earth shelter, whereas, development of conventional housing may not have been possible.
Hilltops provide a special set of characteristics to be weighed by the developer or designer. Light, sunshine, views are plentiful. Drainage and sewerage are easily achieved. However, energy gain is reduced due to the exposure of such a configuration, and accessibility requires large modifications and investments. All of these elements must be accessed to make decisions. Project specific requirements will dictate their feasibility
The soils of a site affect many design considerations to earth shelter development. Soil characteristics lead to design decisions on the amount of earth cover, insulation, and methods of construction.
Soils are generally categorized on particle size. This classification leads to a wide variety of types which present many design variables. Most soils are suitable for earth sheltered buildings; yet, a detail analysis of each soil is necessary to base decisions.
Soil particles are identified by their grain size. Most often soils are broken down into gravels, sands, silts and clays. This rough break down seperates soils into types which exhibit similar properties such as stability, bearing capacity, and water content. These properties are basic to design calculations.
The stability of soil has to do with two aspects of soil mechanics, lateral stability and expansive pressure. Lateral stability has to do with vertical cuts that have to be braced. Lack of bracing can cause cuts to fall in sometimes exerting great lateral pressures. Expansive clays can exert pressures that can also cause eventual collapse of a dwelling. This type of soil is found more often in the High Plains area. Modification of a structure to a non-yield construction
type is usually prohibitively expensive. Therfore, unstable plastic clays should generally be avoided.
The bearing capacity of a soil is the ability of that soil to maintain a load without settlement. This is not as critical a problem in underground construction as it is in above ground construction.
This is due to the fact that air space within the underground structure makes the building lighter than the soil originally removed. In this case, it is possible to build on soft soils and count on them not to settle. The sandy dunes of the High Plains area provide a place in point to utilize this advantage.
Thermal Conductivity, heat retention, and resistance to freezing are determined by moisture content, shape and size of soil particles and the density of the soil. Thermal conductivity of a soil is of great interest in earth shelter performance.
Damp or wet dense soil can consume a large quantity of energy in heating and evaporating the water. Energy required to heat the structure is then lost to this purpose. Whereas, extremely dry compressed soil builds up heat quickly by conduction and in slimmer months can cause the structure to overheat. If arid-zone soils are watered occasionally, this heat conduction can be moderated. Whatever the thermal character of the soil, the structure must reflect this and design costs and decisions must be weighed. Since some soils are more efficient than others, this thermal requirement can affect site selection.
group symbols typical names drainage characteristic frost heave potential volume change backfill potential suggested bearing capacity range (psf) general suitability
GW well-graded gravels & gravel-sand mixtures, little or no fines excellent low low best 8000 psf 1500 psf to 20 tons ft2 good
GP poorly graded gravels & gravel-sand mixtures, little or no fines excellent low low excellent 6000 psf 1500 psf to 20 tonsft2 good
GM silty gravels, gravel-sand silt mixtures good medium low good 4000 psf 1500 psf to 20 tons, ft2 good
GC clayey gravels, gravel-sand-clay mixtures fair medium low good 3500 psf 1500 psf to 10 tons/ft2 good
SW well-graded sands & gravelly sands, little or no fines good low low good 5000 psf 1500 psf to 15 tons/ft2 good
SP poorly graded sand & gravelly sands, little or no fines good low low good 4000 psf 1500 psf to 10 tons ft2 good
SM silty sands, sand-silt mixtures good medium low fair 3500 psf 1500 psf to 5 tons/ft2 good
SC clayey sands, sand-clay mixtures fair medium low fair 3000 psf 1000 psf to 8000 psf good
ML inorganic silts, very fine sands, rock flour, silty or clayey fine sands fair high low fair 2000 psf 1000 psf to 8000 psf fair
CL inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays fair medium medium fair 2000 psf 500 psf to 5000 psf fair
MH inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts poor high high poor 1500 psf 500 psf to 4000 psf poor
CH inorganic clays of medium to high plasticity poor medium high bad 1500 psf 500 psf to 4000 psf poor
OL organic silts and organic silty clays of low plasticity poor medium medium poor 400 psf or remove generally remove soil poor
OH organic clays of medium to high plasticity no good medium high no good remove poor
PT peat, muck and other highly organic soils no good . high no good remove poor
SOILS Suitability for Earth Shelter
These characteristics and potentials for various soils have "been examined for the suitability of earth sheltered structures by the University of Minnesota. They are provided on the preceeding page. This chart will initially aid in site selection Later detailed engineer reports should follow.
Climate, soil types, geology and physical land characteristics comprise an inter acting hydrological system in the High Plains arid environment. Low rainfall, a lack of surface retention and the permeable nature of soils contribute to a reliance on natural underground water storage. Surface accumulation, when it does occur, is usually the results of snow melt or rain storms, which are intense but of short duration.
Large amounts of surface runoff, the soils and a lack of vegetation, cause flash flooding along washes, flood plains, and other basic water routes. The intermittent nature of this area creates a pattern of either too much water or not enough. This hydrological condition poses concerns for the integrated house. Surface runoff, groundwater and aquifer conditions must all be examined to site the underground structure properly.
Ground water,in particular,a high water table, is the one factor more than any other that can Drove the underground house
unsuccessful. A high water table can add enormous expenses for internal water drainage and control. Ocassionally, the soil around the structure can economically be drained. Often this presents subsequent problems of settlement. Thus, avoiding this condition is the most reasonable approach.
The aquifer or artesian condition is an extreme condition of the high water table. The porosity and nature of sidiment layers within the aquifer cause greater horizontal movement than vertical movement. Therefore, if lateral movement is present, the underground structure is more susceptible to problems. Ground water conditions are important to determine because of the impact on water proofing and structural design. High water tables and lateral movement may require great expense.
high water table infiltrates structure
lateral movement causes infiltration
Obviously, submerged buildings built near washes, creeks or natural water routes,that are prone to flash flooding or intermittent level changes, have problems by which above surface structures may not be affected. These areas generally should be avoided by both types of houses. In slight cases waterproofing may provide the answers for the submerged building.
Surface runoff and erosion of a site can actually be improved by integrated architecture. By providing soil on the roof instead of exposing buildings, runoff can be decreased and erosion checked.
The availability of water for social use is also an hydrological concern. If the site to be selected is on a slope or hilltop, it is most likely pumping will be required. All of these aspects of hydrology must be analyzed in the selection and planning of the site.
A number of energy related factors are influenced by site specific conditions. Orientation of landform is the most widely recognized consideration for solar efficiency. Benefits for solar heating on south facing slopes have steadily increased their land values. In addition, slope exposure and radition gain, and wind patterns, and the interaction of these factors produce a climate near the ground.
As stated previously, a southerly orientation provides optimal solar gain. Orientation to the southeast and southwest is also quite desirable. The orientation of structures to these directions is easily achieved on flat lands. Integrating units on slopes usually coincides with the direction of that slope. Therefore, slopes facing southerly directions are most desirable.
Slopes which face east or west provide substantially less access in winter when heat gain is most important. East and west orientations do, however, provide optimal spring and fall conditions. If modifications sire made to structural design and to the amount of earth covered used, these orientation can be accomodating. Housing units can also step down these slopes, presenting south facing facades.
As south facing slopes will be developed
quickly, building on east and west slopes will become necessary. Slopes oriented to the northerly points provide little or no energy value.
Assessing orientation not only leads the developer and designer to sites most suitable for particular projects; it will ultimately influence structural design, landuse and landscaping features.
The amount of radiation or heat gained by the soil is affected by the angle of inclination or slope in relation to the angle of incidence or sun angle. Soil and surface covering also determine heat gain. Significantly higher levels of radiation can be gained by land surfaces that are steeply tilted than can be gained by flat sites or more gentle slopes.
radiation gain is increased
On south, southeast, southwest facing slopes, winter heat gain is increased as the slope increases. Slopes of east or west orientation exhibit this condition only in the spring and the fall. At other periods of the year, radition exposure is greater on more gentle slopes and flat lands. Heat gain on northern exposures is always minimal, yet as the site becomes flatter, reducing the shadow effect from the landform, heat gain is somewhat improved. The amount of sunshine availabel even to these areas is not great enough to warrant the siting of energy efficient homes.
In evaluating a site for energy efficient building these conditions can be classified to offer opportunities and constraints to the project. Increasing use of computer techniques offer greater ease and accuracy determing areas of maximum gain.
Heat gain is effected by wind patterns across a site. In the arid High Plains the prevailing winter winds come out of the northwest, while severe winds are also likely to push east causing heat loss and possible damage. In the summer desirable cooling breezes come from the southwest.
This distribution of seasonal winds can be modified by landforms and by the mixing of winds from other directions. Land-
forms can provide protection or windsheds if their orientation faces away from seasonal movements. Just over the crest of a hill a bubble effect is created. Warm uplifts mixing with downward flows of cold winds create a turbulence area just ahead of a relatively calm zone. The calm area or bubble generally spans five to twenty times the height of the hill and offers varying degrees of protection. This calm area can be somewhat increased by adding vegetation, thereby increasing the height of the hill. Natural windshed areas such as these afford comfort and increase performance of the housing unit.
landform alters wind patterns
Site climate is altered significantly by two other factors. Drainage areas, which effect air flow, and elevation changes. At night cold air moves down drainages ways to the valley below and lingers until daytime when warmed by the sun it reverses its movement. This
phenomenon can cause near loss and unstable climatic conditions if houses are situated to near drainage patterns. Conversely if ventilation is sought after, this phenomenon can be used to a positive effect. On the high plains a combination of protection from cold in winter and ventilation in hot summer monthes is necessary. Siting development in the middle of slopes takes advantage of both concepts.
Changes of elevation bring about changes in ambient air temperature. As elevation increases the temperature normally falls. Over much of the high plains area, elevation changes will not produce wide variations.
Yet on more complex landforms such as the foothills, rises in elevation will produce significant variation. These variations require changes is design strategies.
This section of the study examines the implications of earth shelter on site planning and design. Site planning and layout of the conventional community is generally based on equal lot size, lot shapes which reflect similar relationships to the street and access of all units to utilities. Whether linear or clustered design is enforced, these factors are usually maintained. These factors which affect layout of the community become ^partially altered when designing for. solar passive homes. Providing equal access to the sun requires proper orientation, usually east west elongation of the lot, and careful building placement. Shadows cast by surrounding buildings and vegetation must not interfere with this access. This begins to alter lot configurations and general community layout.
Earth shelter housing presents factors and considerations which modify planning further still. Although shadow casting may be eliminated when buildings are placed on slopes, lot configurations are still altered by orientation requirements. Yet the most critical variable which alters conventional planning principles comes from the integrated aspect of building to land.
The following discussion then is provided to promote a general understanding of the planning principles for the earth sheltered community. Issues such as lot size, densities and layouts are ultimately dependent on the derived form of the structure and site conditions as previously
mentioned. However, generalized forms of the elevational and atrium house can be used here as prototypical units necessary to explore the variables in planning for the integrated community.
An elevational structure 30 x 70' with a rectangular proportion of 1:2.4 has been selected as a prototypical unit. Planning variations for the atrium house are base on a 50' x 50 structure with a 500 sq. ft. interior court.
LOT SIZE ELEVATIONAL
The elevational house is positioned south to collect solar heat on its longest facade. This results in an elongated east-west axis. When placed at grade on a flat site, a rather large lot is necessary to achieve integration. Berming around the structure necessitates much of this land requirement. Maintaining thirthy per cent slopes on all berms requires 35 feet of land on each covered side of the building. An additional 10 feet is necessary to insure proper drainage. Forty five feet of land then is necessary on each of the three covered sides of the elevational structure.
These large berms created by placing the building at grade are usually unsuitable for outdoor social spaces. Land fronting the south facing facade becomes then, the usable yard space. Creating a privacy patio enhances this adjacent space. In this case a 500 sq. ft. patio was selected.
An allotment of 50 feet has been made for total front yard use.
With the combination of front yard space berm,and drainage requirements, the result ant lot size becomes 125' x 160'. This lot of 20,000 sq. ft. is necessary to integrate the elevational house on a flat site.
elevational house on a flat site
Lots can be made smaller by the use of extensive retention walls or by recessing the elevational house. Recessing the structure reduces berm requirements. The amount of land saved is dependent on how deeply the house is placed. Recessing the structure, however, effects entrance and and vehicular access. The designer, there fore, has the opportunity to choose the option most suitable to project require-
As the slope increases, land requirements diminish. Integrating the same elevational house on a ten per cent slope reduces the lot size. Berming is eliminated at the rear of the building and although,
10 ft. for swaling is still required for drainage, the north-south axis is reduced by 35 feet. On the sides of the structure drainage requirements are unnecessary due to the natural pitch of the land. The size of the berms are also somewhat reduced, although not eliminated. This results in a ^0 ft. abatement. Lot size on the 10 fo slope then is reduced to 90' x 120' ft. or 10,800 sq. ft.
elevational house on ten percent slope
On the twenty per cent slope two story units can be integrated. The two levels are staggered or stepped down the hill. Front patios or pribacy spaces can then be placed atop the first level, thus reducing front yard requirements. Rear
lot drainage is still maintained, yet side lot demensions can be reduced further. To integrate the elevational two story on a twenty per cent slope requires a lot size 80' x 90'* or 7200 sq.ft.
The variation of lot sizes for the atrium dwelling is based on similar criteria as that of the elevational house. The atrium house, however, requires no fixed solar orientation, thus the east-west elongation of the lot is unnecessary. Usually the nature of atrium design is to fully recess the building. On a flat site this eliminates all land requirements for berming Ten feet of land is still demanded on all sides for proper drainage, while front yard space is minimized to twenty five
feet. This usually fullfills normal front yard setbacks. The lot necessary to recess and integrate the atrium prototype then, becomes 85' x 70' or 5950 sq. ft.
recessed atrium on flat site
If placed at grade on the flat site, the atrium requires 35 feet for berming and 10 feet for drainage on all covered sides, just as the elevational. A lot of l40'x 1^0' is needed to fullfill this position. Positions in between at grade placement and the fully recessed atrium like the elevational, change the size of land parcels.
On the ten per cent slope, the totally covered atrium requires a lot 105*x 120' or 12,600 sq. ft. Drainage is eliminated at the sides due to slope. Yet, front
coverage and drainage increases front yard requirements. Often the atrium undergoes somewhat of a design change on islopes opening up the south facade to act similarly to the elevational unit. This increases views, and heat gain while land requirements decrease. Necessary lot sizes for the exposed facade atrium then, become 85 x 120' or 10,200 sq. ft.
exposed atrium on a 10% slope
Atrium housing, even with exposed elevational design is usually not built on slopes greater than 10 to 15 per cent.
The shape of this unit, requiring larger lots and increased excavation, generally is found unsuitable for the steeper terrain.
As seen from the discussion above, as the slope increases the amount of land
necessary for integration decreases.
Thus as slope increases so does density. This of course is one of the advantageous aspects of earth sheltered design. Slopes unsuitable for conventional buildings are now available for dense development.
Based on the arrived lot size for the elevational house and the atrium design, the following densities can be acheived on the various slopes.
DESIGN TOPO LOT SQ FT UNITS
elevation flat 125x160 20, 00 2.2
one story 10% 90x120 10300 4
two story 20% _ 80 x 90 7 200 6
atrium-recess flat 85 x 70 5950 /.3
atrium-grade flat 140x140 19600 2.2
atrium 10% 105 x120 16,800 2.6
exposed 10% 85x120 10,200 4.2
Solar placement of buildings, lot sizes, and acheivable densities serve as guides in laying out the earth shelter housing complex. Yet the ultimate design which results from the combination of these factors must, as with conventional housing,
respond to site conditions, accessibility for roads and utilities and social cohesiveness. In the past many techniques in site planning for the single family detached house were developed in response to these issues.
One of the earliest patterns developed was the typical grid system. Lots laid out in rectangular pattern were surrounded on all four sides by access streets. In an effort to reduce economic pressures and preserve land, site planners turned to the cluster technique. Clustering housing units not only reduced the extensive road and utility system demanded by the grid layout, but adapted to land patterns and preserved more of the natural landscape. In addition, the clustering of homes around the cul de sac provided a social unit unknown to the grid system.
The cluster alternative also proved to have slight energy benefits. The close proximity of units served as protective breaks from winter winds. Yet, when energy conservation became even more imperative, the solar community concept developed. Clustering houses became more difficult. Houses in the cluster arrangement cast shadows upon each other reducing solar benefits. Out of a necessity to supply houses with uninter-ferred solar access the layout of the community took on a linear appearance.
Rows of houses faced south to passively collect the sun. East-west streets served as access to units. This layout accomodated solar access and energy conservation, however, the efficiency of shorter roads and
utility lines and the social cohesiveness of the cluster pattern was lost.
When site planning for conventional homes and solar passive homes, the cluster layout and the linear layout respectively are the most widely used techniques. Applying these patterns to the earth shelter house form presents yet a different set of considerations.
Building a community or housing complex on slopes at once implies a verticality which does not ordinarily exist in most housing sites. This vertical nature effects social relationships as well as road and utility layout. A second consideration in laying out the earth shelter complex is the integrated nature of the form. The integration of homes and earth creates a complex physically defined by the third dimension. Whereas, definition of space in the above ground community is implied by house form and negative space, the earth cover of subterranean houses place close together becomes a physical sculpture.
In different site conditions both the linear and cluster layouts can be approp-iate for the earth shelter form. With these new considerations in mind, these site planning techniques need new clarification. The following discussion brings to light issues associated with linear or cluster layout.
The solar passive elevational earth shelter house when placed on a flat site or on very gentle topography requires similar conditions to the above ground solar pas-
sive home. Placing houses in close proximity can create shadow casting from surrounding structures or terms. The linear layout of houses can he used to eliminate this problem. With the houses oriented to the south, east-west roads provide access and carry utilities to individual units. Due to the east-west elongation of lots, roads and utility lines can be quite extensive. Since north-south dimensions of lots are somewhat shorter, north-south roads and side lot access to homes can somewhat improve this situation. A side benefit of this layout is protection of front yard privacy for all units.
east-west roads demand longer roads and utility lines
north-south roads can decrease requirements
When steeper slopes are utilized, the problem of shadow casting is eliminated.
Yet, a linear layout with east-west cross slope roads may be necessary to provide access. The possibility of north-south roads on the south facing slope would be infeasible due to the steeper incline.
The extended cost of access and utilities would be moderated by the increased densities possible on steeper terrain. The possibilities of building on such terrain, normally unusable may also compensate for the disadvantages of this layout.
Actual dimensions for the linear layout will vary. As previously discussed, lot sizes and densities are some what dependent on topography and methods of integration. The physical grading concept, however, can also effect layout. Units can be bermed individually or placed closer together to share longer common berms. This manipulation serves a variety of functional and visual requirements.
Social interaction of the linear arrangement is predominantly lateral. On flat sites, cross street face to face interaction is reduced by rear berms. On steeper slopes units across roads and open space are integrated at lower levels creating a terrace effect. Yet, access to roof tops and enhancement of roof top space can improve communication between successive levels of the complex. Various design treatments of this nature can be used to overcome the vertical stratification physically created.
roof top treatment can reduce vertical stratification
The clustering of detached units is an alternative technique suitable on sloping land that is not is excess of 20 per cento It can also he used on flatter sites when a combinations of elevational and atrium housing is possible Elevational units accomodate upper slopes, while atrium units either fully recessed or bermed at grade, fit the cluster pattern without interferring with solar access.
On sites with slope situations, clustering units around a cul de sac or auto court creates a level pocket with houses set into hillsides above and below. Side units can be recessed or built at grade to acheive the spacial definition desired. This centralized scheme reduces roads and utility lines necessary to service each unit while creating a social pocket or area of increased interaction. Densities can be increased while more surrounding landscape is preserved.
clustering creates a social pocket and reduces access requirements
On flatter sites access routes are more flexible. The possibility of the central pocket serving as open space for the cluster presents itself. Vehicular access to units takes place through rear berms.
This option provides increased cluster privacy and social cohesiveness.
The centralized auto access also reduces the visual impact of the automobile across slopes. By varying the recessed nature of units and the integration of berms, the cluster pocket can be spacial defined.
Surrounding berms and open space can then provide a more natural image than the linear arrangement.
Actual cluster size, as with the linear layout, is dependent, on topography, decisions of unit integration, and grading concepts. Manipulation of these variables to acheive desired requirements of the project can result in a great many variations .
In summary, the linear method of planning presents the advantage of easy access and reduced disturbance when building on very steep slopes. It also provides equal access of the sun to elevational units placed on flat topography. Advantages of the cluster technique are increased social interaction, a more natural environmental image and a reduction in utility and access requirements. In either layout the creation of berms for earth cover adds further spatial definition to the housing complex. The combination of housing units then, serve as a base to create a community of sculptured landforms.
The previous sections of this document have served to briefly discuss the design elements associated with earth sheltered development. A synthesis of these considerations and variables produce general principles which can guide the designer or developer. These principles are the tools necessary to respond to forces of physical land condition, climate and energy conditions, and social functions which ultimately sculpt the community.
. The surface relationship of the earth shelter unit is a variable factor which can be used to respond to varying terrain, climatic pressures, and social situations.
. The amount of earth cover submergence, or penetration is a response of climate, yet can also regulate physiological needs and psychological comfort, while promoting social interaction.
. The earth shelter structure and surrounding adjacent spaces form the functional energy system of the unit. Regional and site climatic conditions are the forces which shape the ultimate form. Orientation, exposure, volume to mass relationships, and adjacent landscaping are the variables which can be manipulated to create a variety of responses to these forces.
. Lot sizes decrease with slope and
submergence, thus increasing densities.
While these factors are constant, units can be selected and combined to create a variety of layout designs and functions.
. The overall spatial quality or three dimensional sculpture of the earth sheltered community is manipulated to promote access, and social interation while preserving privacy.
. Landscape of the community includes new spaces such as rooftops and sunken courtyards. New alternatives must be utilized which improve social interaction, and avoid vertical stratification.
The synthesis of these principles is by no means complete. Hopefully, it will, however, begin to serve as a guide for introducing a new typology to the Arid High Plains in an effort to create communities compatible to new goals and nature.
THE CASE STUDY
To test the applicability and feasibility of concepts developed in previous sections of this document, a case study was undertaken. Locating a parcel of land situated in the Colorado Piedmont or Rocky Mountain outwash, which exhibited typical conditions of the stressed climate, the developers of Lake Valley Estates graciously permitted the use of this parcel as a study area.
The Lake Valley Estates property consisting of approximately $00 acres is located three and one-half miles north of the incorporated area of Boulder, just east of the foothill formations and Foothills Highway. To the northwest section of the study area lies Left Hand Valley Resevoir. Lake Valley Estates previously was used as agricultural land and surrounding land to the north, east and south is yet occupied by agricultural homesteads .
Within the decade of the 60's, Lake Valley Estates was initiated and planned as a total community. Radiating from a commercial center and golf course, neighborhoods of various densities and economic levels were planned to meet the needs of the growing Front Range. Two elementary schools and a secondary level school were planned to fullfill the community's educational needs. A conceptual plan of this total community can be seen on the following page.
LAND USE CONCEPT
LAKE VALLEY ESTATE
To date, the total community concept of Lake Valley Estates has not been developed. The golf course is functional and single family housing in the western section of the study area has been developed.. Actual fullfillment of the total community concept is currently still under negotiation.
Within the community, in the northwest section of the study area lies a forty five acre land area designated for single family development. Comprised of south facing slopes, this area is borderline for conventional housing and has been selected as the site to be designed for this case study. This case study then, will examine and analyze this site for potentials of development and propose a plan for an earth sheltered neighborhood which can appropiately be integrated within the community concept.
In order to identify the best locations for detached earth shelter housing a number of site development considerations have been inventoried and analyzed. Natural systems of geology, soils, hydrology, and slopes were mapped in order to delineate site conditions. Also mapped, were energy potentials of orientation, slope exposure, and winds. Cultural features of the site were also recorded in this manner.
Combining this information by use of an overlay process, a devlopment suit-ablility composite was compiled. This composite marks areas in which development can occur and indicates design criteria for that development. Once these development areas were determined an overall comcept was determined to integrate the site with the Lake Valley total community. Alternative site design concepts were then selected and applied to illustrate the earth shelter community.
The following pages show these sequential phases of inventory, analysis, and development concepts which are finalized in community design.
The Lake Valley Estates property is underlain by thousands of feet of sedimentary rocks These sediments are the results of broken down parent material washed out from the Rocky Mountains. Across the site selected for development, three geological courses exist. Underlying the property, the bedrock unit of Pierre Shale is *4-000 5000 feet thick. Pierre shales are olive gray shales and interbedded brown fine grain sandstones. This bedrock layer is blanketed by up to 20 feet of Slocum alluvium deposited by a combination of mountain stream action and glaciation.
The Slocum alluvium is a cobbly or coarse gravelley deposit consisting mostly of Precambrian crystalline rocks.
Over time these rocks have been altered by weathering and mixed with and enriched calcium carbonate deposit.
In the lower section of the site, more recent Piney Creek alluvium has been deposited atop previous layers by movements of Left Hand Creek and Dry Creek. Silt, sand,cobble and gravel have been laid down from this water action. Medium to dark gray clayey sandy silts from Dry Creek form terraces up to 20 feet thick above the modern stream. In areas this
alluvial action has cut through Slocum layers exposing the underlying Pierre Shale unit.
Regionally these layers all dip to the east, but across the Lake Valley property this dip is interrupted by the Haystack Mountain anticline causing local variations. No geologic faults occur across the site and subsidence is not a problem.
In summary, geological concerns are limited to the erosive nature of alluvial deposits., Development which avoids patterns which tend to cause erosional damage should be followed.
piney creek alluvium
In the upper part of the site, the Slocum alluvial outwash fan has produced a soil known as Valmont cobbly clay loam. This soil has a surface layer of cobbly clay loam about 8 inches thick. The subsoil is about 14 inches of cobbly clay loam slightly thinner. Runoff is medium on this soil making erosion hazards slight to medium. Due to the cobbly nature, vegetation is limited to grasses and previously has been used as native range. Shrink swell capacity is also moderate due to the cobbly mixture.
Down the face of the sites slopes the soil condition is known by the term terrace escarpments. This condition varies significantly from site to site and has no general Soil Conservation Serice Interpretation. Yet terrace escarpments across the site are a combination of broken shale and Valmont subsoil which have been eroded by water and wind.
Also very cobbly in nature these soils exhibit moderate shrink swell. The erosive characteristics of the soil are similar to the Valmont soils, yet due to the increased slop, increased runoff can cause more problems. Grasses, therefore, are somewhat interrupted and invasive plants such as yucca are more dominant. Slowing runoff on these soils increases vegetative capacity and soil loss.
Dry Creek runs along the lower section of the site, and the central area drains
the upper terrace into the creek. Along these drainages a clayey soil known as Renohill exists. This soil has slow permeability and is highly expansive in nature. Subject to periodic wetness and drought, Renohill soils tend to be unsuitable for the possibility of housing whether it be conventional or earth shelter. Renohill soil differs from the other site soils also, in that the bedrock layer can be found at a shallower depth, thereby reducing diggability.
In summary, the upper site and slope faces are compatible with development if erosional forces are planned for and checked. These soils may produce small variations from place to place which would require design variations; but generally these soils would be suitable for integration of the earth shelter house. Wetness and the expansive nature of land surrounding the drainages preclude building. These restricted areas should be respected for their present site functions.
valmont cobbly clay loam
As Left Hand Creek descends from the foothills onto the Plains, it is captured and contained in Left Hand Valley Reservoir which borders the northwestern section of the Lake Valley property. There Dry Creek flows from the reservoir across the study area until it crosses the lower section of the designated site. This section subject to periodic flooding and wetness lies within the 100 year flood plain.
A drainageway, intermittant in nature, collects runoff from the outwash terrace above and as it splits the site in half, comes to rest in a small basin centrally located. This area stands in water much of the high runoff periods of the year, and exhibits marsh like characteristics.
The remainder of the site is steeper slopes and subject to drainage by sheet wash action. Although much of this sheet wash flows across the flat lands below, the eastern section of the site drains into the Dry Creek Channel. Due to the agricultural irrigation ditch located north of the site, sheet wash runoff has significantly been reduced.
Subsurface conditions which would prohibit development are limited within the site. Lateral movement does not occur through the slope soils. Along the lower flatlands and Dry Creek periodic raising of the water table would present develop-
The Hydrological concerns within the site, then, are restricted to the lower southeastern area, 30 feet north of Dry Creek to the southern boundary line, and the central drainageway and its collection basin. All remaining areas exhibit positive drainage and dry subsurface conditions.
high water table
The topography is largely one of steep slopes falling away from the outwash terrace at the upper portion of the site, into flatlands to the south and southeast. These slopes vary in degree of steepness across the escarpment. The site has been mapped to show this variety and delineate areas suitable for various housing and designs.
Slopes 0 -5$ occur in the lower southeastern section and central section of the site. These relatively flat lands are suitable to conventional housing and atrium design. On 5 8^ slopes, which rise from the previously mentioned flat areas, all types of design, conventional, atrium and one story elevational are possible. Slopes of 8-15$ exhibit the same opportunities, although conditions for conventional housing are becoming borderline. Slopes of 15-20$ can accomodate one story and two story elevational design.
A relatively small portion of the site has a slope of less than five percent.
On the other hand, a relatively high portion of the site has slopes in excess of eight percent. Since these steeper slopes are preferable for earth sheltered housing, yet unsuitable for conventional building, tne designated site may become usable for community development.
: \' V ' ' T : r c
n o_ 5%
Homing TVpe______0~5 5~8 ff15 15~2Q
Passive Solar w
One Story e
a Two Story
o m m
The selected site has been mapped to delineate orientations of the landforms and their variations. This map is created by demarcation of all ridges and valleys. Landforms are then seperated by planes that reflect eight different directional orientations. Orientations have been seperated or grouped on the basis of criteria discussed in preceed-ing sections of this document.
Slopes to the south, which are most desirable, are delineated in black. Southeast and Southwest facing slopes, which are also desirable are represented in diagonal and cross hatch markings respectively. Slopes toned by dots mark the east and west orientations.
These slopes are usable if design variations offset less opportune solar conditions. Northern orientations and flat lands have been represented in white. These areas collected little heat gain from solar positions, or in the case of the flatter areas, orientation is not an issue.
Solar orientation is an important factor in reducing energy for any of the alternative designs. Although convention passive housing can more easily capitalize on southern exposures by design variations, earth sheltered housing is usually integrated on sloping sites in the direction of the slope face. There for orientation mapping is more crucial.
Potentials are very good for the site. A large majority of the land is oriented to the south, southeast, or southwest.
a*l / wm(
The amount of radiation or heat gain available to the soil is dependent on the angle of inclination,(slope) sun angle, orientation, and surface material as previously mentioned. Determined slope data orientation and surface conditions (uniform grasses) were combined with seasonal sun conditions for the Boulder latitude. Utilizing a computer, this information was analyzed and available heat gain for various conditions was calculated.
Based on this data, varying areas of energy efficiency were mapped for development considerations. Areas of optimal gain throughout the year are represented in black. These areas are the steeper slopes of south, southeast, and southwest exposures. Slopes oriented to the east and west gain more radiation as the slope becomes equal to the angle of incidence. East facing slopes, depicted in diagonal markings, are optimum only in the morning hours of spring and fall. Western slopes or the cross hatched areas are optimum in the afternoon hours of spring and fall. Designs for these areas must offer offsets for these secondary solar conditions.
Northern orientations, flat lands, drainageways, and terrace ridges offered no appreciable gain of radiation due to sun inclinations, wind exposures, and cold air movements.
The designated site offers a large por-
tion of land in which energy gain is possible. By manipulation structure design, landscape development, or lot layout east and west exposure areas can be added to increase this area.
The severe wind direction across the Lake Valley property and selected site is westerly., Over 50 percent of winds throughout the year come from the north, northwest and southwest. Cold winter storms originate from the northwest.
From December to April, Chinook winds drop over the foothills and blow across the site. These severe winds can exceed 60 miles per hour.
During the spring and summer, prevailing winds travel from the southeast bringing rainstorms and cooling breezes.
In general the winds across the site can change rapidly. Within the twenty four hour cycle air flow also shifts.
At night cold air flows eastly from the foothills and reverses its movement during the daytime hours. The speed of this air flow is minimal, yet drops in temperature can result along the drainage-ways .
The physical nature of the landforms within the site offer very little natural windshed protection. Severe westerly winds can whip across most of the south facing slopes of the site. Only a very small portion of the site delineated on the following map offers shelter
The nature of earth shelter or subterranean building, however, offers its own
protection and reduced infiltration.
Yet, development concerns regarding wind movements across the site should limit possible erosional problems and reflect architectural solutions in design. Entry spaces, outdoor adjacent spaces, and community layout should be designed with associated wind problems in mind.
Besides the natural and energy consid- erations of the study site, there are additional site features which will have a form giving effect on the development. These are the view of the site and cultural features already existing.
As the south facing slopes of the site fall away from the outwash terrace to the valley land below, they offer excellent views to a variety of regional features. The south facing slopes offer a wide angle view across the valley to the Flatirons of Boulder. Slopes turned slightly southeast present the image of Haystack Mountain, just east of the site. Views from the west facing slopes scan the golf course in the bailey and finalize in the rise of the foothills.
From any position of the site the long range visual features are excellent. Fore range visual aspects will necessarily change with development. Two existing features, however, present visual constraints to the site. In the lower southeastern section of the site, the Lake Valley Estates sewage treatment plant is situated. Just west of the central part of the site lies the golf course clubhouse and parking. Both of these features require design treatment to modify the negative visual effect.
The existing road which borders the southern edge of the site is the Lake
Valley Drive loop road. This road serves the entire community in a collector capacity. All circulation within the new development will be more private in nature and connect to this main circulator.
The form of the development will also be influence by the existance of an agricultural irrigation ditch which crosses the northern boundary. This irrigation structure services agricultural homesteads, on the outwash fan above. Water is carried intermittently. Development of this area of the site is restricted, yet the irrigation structure and easement area can serve as an open space amenity apd will necessarily influence development considerations.
mtwm existing road
The two areas designated as area B share 8 15 percent slopes which face south. Units built in these areas as in area A need not be manipulated for solar gain. Housing in area B will, however, change to the one story elevational and the exposed atrium design. This reflects the change in topography. Lot sizes will also need to be larger for increased berming.
The south facing slopes of area C are even flatter in nature then other areas. The units which respond to this area can either be the one story elevational or the atrium. This flatter terrain, however, offers less slope exposure or radiation gain. Larger lot sizes are also necessary. These factors can be compensated for by semi recessing the units. Additional earth moderation and sunken patio-gardens can gain greater energy benefits. Lot size can also be reduced by recessing the unit. The more private nature of semi-recessed units will also have a positive effect within area C, as these sections are the closest levels to the existing collector loop.
In keeping with the objective to make each dwelling energy sufficient by solar means, area D housing will require the
most manipulation of design. Slopes of this area face east or west. Units will respond to this condition by stepping down the hillside presenting what would normally be the side of the unit to the south as collecting facades. Adjacent outdoor areas then will be terraced with the levels of the house. Changing the unit to reflect energy conditions will effect a change in lot shape and size within the D areas.
Although the nature of the house, lot, and density will change from area to area, the entire area suitable to development will be integrated and governed by the design concept.
slopes orientation lot sijfe
two story elevational 15-20% south 80x90
one story elevational atrium 8 -15% south 90x120 85 x 120
semi/ recessed elevational atrium 0- 8% south 125x140 105x120
elevational adapt form to solar 8-15% varies 120 x 90 .
SUITABILITY FOR HOUSINGS^
The areas suitable for housing and the remaining neighborhood open space were de veloped into an overall neighborhood concept based on the following goals.
1. The single family site will be integrated to the total planned development concept of Lake Valley Estates.
2. The alternative chosen for housing layout will be consistent with the community concept yet, illustrate the application of principles associated with earth shelter housing.
3. Housing layout, placement and land scaping will reflect principles of energy efficiency.
4. The design concept will provide for social needs and enhance interaction with in the community.
The discussion below and the Cluster Schematic which follows summarizes this concept of development for the site.
THE NEIGHBORHOOD CONCEPT
The drawing below graphically reiterates the total community concept of Lake Valley Estates. High density housing, town center and educational facilities surrounded by the open space of the golf course are centralized within the community, This central core of development
is then bordered by lower densities and single family parcels. Throughout the Lake Valley Community, the cluster form has been used to maximize open space.
The circulation loop serves to collect and distribute all traffic around the development. Pedestrian circulation paths are separated from vehicular patterns, yet serve similar functions Integration of the site has been acheived by a continuation of this concept.
The cluster alternative is continued within the single family site in order to maintain the character of the total community. The cluster concept also provides
an opportunity to illustrate an alternative to the vertical social stratification which results from linear terracing. Clustering the housing of the site rather, will create pockets of social relationships.
All areas suitable for housing are at once unified by this cluster concept. Yet, within the cluster, house design may vary reflecting criteria of individual areas as previously discussed. Cluster size will also differ, due to a variety of lot sizes necessary for varying slope conditions .
Circulation to the developed homesites will be via roads of the Lake Valley Drive circulator loop. The configuration of this system will be a series of short roads terminating in cul de sacs.
The cul de sac system has been chosen to reinforce the private character of the neighborhood by reducing vehicular traffic passing directly by homes. The system will cross slopes to reduce excavation and construction costs, and to reduce disturbance of landforms as much as pos--sible.
Cul de sacs will also be used as auto entries and create a central point for cluster layout. The majority of homes are sited on these cul de sacs. A small portion of homesites in the western sec-
accMs and utility lines are centralized by cul de sac
tion will have direct access to the circulator loop due to the limitations of the land configuration and steep slopes.
The cirulation of Pedestrian traffic within the site will connect walks generating from housing clusters to the main pedestrian circulator path. This walk placed within the open space of the site rims along the northern portion of the site proceeding west to the town center and southeast to the educational facilities of Lake Valley Estates.
The landscaping scheme for the site is a response to energy requirements and site conditions. To the north of the proposed housing, windbreaks are provided. These windbreaks serve to reduce discomfor from prevailing winds and to enhance the energy efficiency of individual dwelling units. Desiduous shade trees are used to enhance
the summertime operation of the energy efficient dwelling.
In response to site conditions, screens? have been supplied to block constraining views of the sewer plant and golf course, parking. The balance of the site is left undisturbed or will be revegetated with native grasses to retain the original character cf the site.
# common auto entry
pedestrian circulation community collector
THE SITE PLAN
The site plan which follows, illustrates the implimentation of the design concept. This preliminary design shows the adaption of the cluster layout to the specific site conditions.
The large south facing slope in the eastern section of the site contains three large clusters. A total of 30 units have been placed in this portion of the site.
The terrace to the north, the ridge line to the west and the sewer plant to the south, physically contain this sloping area. This places units across the middle of the slope avoiding wind movements of the upper terrace and cold air drainage along Little Dry Creek.
South facing elevational designs have been utilized in the steeper upper portion of the slope. Combinations of elevational and atrium houses occupy the less steep terrain of the central section. In the lower flat portion recessed atriums are used to adapt to the terrain. Entries to these lower units are placed at grade to facilitate vehicular access and to overcome the underground nature of the unit. This provides a pleasing entry image. All units have direct auto access, while guest parking occurs along the street or within the auto court. Positions of the units obstruct the auto impact across the slope.
The central portion of the site continues
a similar cluster layout. Houses in the eastern central section change when necessary to acheive proper solar orientation and increased energy benefits. Upper units within this cluster face south-south-west with no alterations. Yet central units must step down the hillside using the staggered facades as collectors.
The western flank of the central portion is occupied by elevational houses on steeper slopes and atrium units in the low areas. Again atrium housing in this area is fully recessed. These two clusters of the central section are contained in the bowl like area and bisected by open space required to properly protect the natural drainage of the site.
The western section of the site limited by property lines and the upper irrigation ditch, presents a configuration by which the cluster form must be modified. Building placement in the western part of this area is restricted to units placed along the existing road. The eastern portion provides ample area and slope for six elevational units placed in a modified cluster arrangement. Due to the steep terrain, however, it is necessary to detach garages within this cluster layout.
Total units number 58 across the site.
The layout of these units illustrate the variations of lot sizes and densities appropiate to the changing terrain.
A statistical summary of land use shows the ultimate acheivement of this cluster arrangement.
Residential lots (58) 13.2 29.16
Internal Roads w/ROW 2.2 k.Q
Open Space 29.6 66.0k
Total 45 100%
The conceptual site plan illustrates concepts and principles set forth in previous sections of this document. Varying the surface relationships of units, adapting units for energy benefits, adapting lot sizes and densities to terrain, and manipulation of layout, landscape, building designs for social enhancement have all been incorporated. Yet, the acutal design of the site reveals something more. That is each site offers a unique set of conditions which will influence the eventual implimentations of the principles. Principles which guide the community layout are strongly governed by land-forms and availability of access routes.
It can be seen, therefore, that the principles associated with earth shelter development, set forth in this document, are generalized guidelines awaiting the refinement of a creative and imaginative designer or planner. The combination of all these forces will shape the earth sheltered community.
E levat ional
Elevational Road Atrium
It is apparent upon completion of this study that conclusions to the subject of Earth Shelter are premature. What arises in place of conclusions are additional questions. We have just begun to scratch the surface of the underground concept.
A rich physical heritage exists to show the continuity of Geotecture. Yet, we inherited no understanding or identification of the subject itself. Patrick Horsbruch, (Department of Architecture, University of Notre Dame), points out that
"no academic discipline has emerged, nor has any scientific recognition been given to the subject of geospace. By 'indirections' then must we find out the 'directions,' the historic experiences, the modern justifications and the design disciplines of geotecture. By the indirections of competitive economic and conflicting planning purposes, shall we be forced to find the values of geospace and the economy that geotectural 'directions' have to offer in what to do, and how to make use of that almost solid and almost infinite realm beneath the surface of the earth."
Throughout the history of mankind, it can be seen that energy is the basis of civilization. The dissipation of energy that occurs at the hands of each success-
ive culture ultimately causes its demise. Our culture today is the most intense high energy society ever. Therefore, we are also the most vulnerable. Bending over from the weight of our present practices, we have been forced to see the ground. By this "indirection" have we come to see potentials of building in the earth.
Yet, other "indirections," a degraded environment, an increased competition for agricultural land, and overloaded sensory systems force us to look to the earth.
We see a radically new idea of the subterranean community. New ideas require research, data compilation, coordination, and trial designs, all of which are limited. And so we begin .
Begining to design with the earth shelter concept, you begin to notice something is different. Of course, it is underground. Yet, something more subtle, illusive at first, seems to govern the design, the form. It is different. But what is it?
For centuries using the concepts of solid geometry, architects and sculptors have created forms in space, seemingly in a vacuum. In contrast, the geometric forms created by geotecture are voids carved from the solid. This reversal .requires a new sensitivity. A sensitivity to subtle form/surface relationships. The interior environment is created by what is removed not what is enclosed. At the same time, what is removed also definesr the surface relationship and creates the
outside environment. The subtle boundaries created by combining the positives and negatives of the world above and below will require new dimensions in the thinking process.
As planners and designers of new communities, this defining trait of earth shelter requires alterations. The term planning itself implies a focus on the plan and has manifested a concentration on the horizontal plane. Square footage, and areas are created, lots are platted across the land plane. Yet, now as planners and designers, it is important to think in terms of cube footage, vol-umns and mass. An expansion of dimensional thinking must begin to permeate.
The subtle boundaries of earth shelter which expand our dimensional thinking are not limited to the geometric or spatial world. Returning to the earth for shelter creates a society of land and sky. Returning to the earth revives a connection. This connection expands our vision and redefines our world. Replacing separation, specialization, etc., with the connectedness of all things may push us forward to a healthier environmnet. The expansion of dimensions may cause us to stop fouling our own nests.
New dimensions of thinking and living will require new languages, behavior, tools laws and codes. The dimensional world below cannot be governed by practices of the world above. Understanding of what the implications of earth shelter are has
just started. It is a new beginning .
This document has attempted to set forth a variety of principles and variables associated with earth shelter, in an effort to guide us through some new dimensions. Using these guides to design new communities in accordance with the sculpting forces of land, water, wind and energy, hopefully will lead us to communities which are biologically correct. There are no radical departures within this study. It is rather a conservative step forward. As we continue to understand geotecture and the environment of the Arid High Plains, principles will be modified and expanded, designs will take on new meanings and society of the earth will grow.
And yet, it is a new beginning .
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