earth sheltered housing an evaluation of energy conservation potential

8/13/2019 Earth Sheltered Housing An evaluation of energy conservation potential.

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O A K RIDGE N A T I O N A L LABORATORYU N I O N C A R B I D E C O R P O R A T I O N

N U C L E A R D I V I S I O N

O P F R A T i I f l L3Y

P O S T OFFICE a o x xO A K R I D G E , T E N N E S S E E 37830

A p r i l 20, 1982

To: R e c i p i e n t s o f S u b j e c t R e p o r t

Repo r t No.: ORNL/COM-86 C la s s i f i c a t i o n : U n c la s s i f i e dA u t h o r : R. L. Wendt

Ea r th -She1 te re d Housing, An E v a l u a t i o n o fE;nergy C o n se r va t io n P o t e n t i a l ----ub ec t : l llERRATA

P le a s e n o t e t h e f o l l o w in g c o r r e c t i o n s t o O RNL/CON-86:P-24 Change the second re ference 11 ( l a s t l i n e o f page)t o r e f e r e n c e 12P-27 Change reference 12 t o r e f e r e n c e 13Change re ference 1 3 t o r e f e r e n c e 14C hange r e f e r e n c e 1 4 t o r e f e r e n c e 1 5P-28 Change re ference 15 t o r e f e r e n c e 1 6D e le t e t h e s e c o n d r e f e r e n c e 16 ( l a s t l i n e o f s i x t h p a r a g r a p h )

R . * L . Wendt

RLW: saa/a


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Contract No. W-'7405-eng-26

ENER GY DIVISION

E A R T H - S H E L T E R E D HOUSING,AN EVALUATION OF ENERGY-CONSERVATION POTENTIAL

R. L. Wendt

DEPARTMENT OF E NE RGYOffice of Buildings Energy Research an d Development

Buildings Division

Date Published: A p r i l 1982

OAK RIDGE NATIONAL LABORATORYOak Ridge, Tennessee 37830

operated byUNION CARBIDE CORPORATION

for t h eDE PART ME NT OF ENERGY

3 4456 04521308 b

.


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TABLE O F CONTENTS

ABSTRACT vINTRODUCTION 1EARTH-SHELTERED HOUSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Scope 3Descr ipt ion of Ear th-Sh el tered Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Factors Inf luencing Energy Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4EVALUATION O F T H E C O N C E P T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Energy Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Applicabili ty of the Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

. .31arketabili ty of the Goncept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CONCLUSIONS . . . . . 43. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .R E F E R E N C E S 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ADDITIONAL4 SO IJRCES O F INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

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ACKNOWLEDGMENTSThe author gratefully acknowledges the efforts of the Oak Ridge National TAaboratory

s taf f members who s ignif icant ly contr ibuted to the product ion of this document : L. F.Truet t , edi t ing and coordinat ion; L . D. Gilliam, graphics and makeup; C. L. Nichols, secre-tarial assistance and composition, 11. B. S h a p k a , G. A. Chris ty , S. El. Brite, and M . Yost,analys is of energy and cos t compar isons ; and 6 E. Courville and J. W. Michel, who gaveadvice and guidance. In addition, the support and cneouragement of J. J. Boulin, Depsrt-me nt of Energy, contrib uted significantly to the acco mplishme nt of th is document.

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ABSTRACTThe ITS. Depa rtmen t of Energys Innovat ive St ruc tures Program (ISP) began a n evalua-

t ion of the energy conservat ion potent ia l of earth-shel tered houses in late l979. Since t ha tt ime, severa l pro jec ts have been un dertake n by the ISP a s p a r t of th is evaluat ion . The f ind-ings of these projects, plus a discussion of the work of others in the field, form the body ofthis report . Al though a comprehensive evaluat ion of ear th-sh el tered housing ha s not beencompleted , th is rep ort presents a compendium of knowledge on the subject . The conclusionsof this repo r t are more qual i ta t ive tha n quant i ta t ive in n atur e because of th e limi ted infor-mat ion on which to base proje ctions . However, the se conclusions will, in all likelihood,rem ain reaso nably valid even with in-depth investigation.

The major conclusions to dat e ar e as follows:Earth- shel tered houses are capable of very good energy performance. Therm al in tegri tyEac~ ors ang ing f rom abou t 1 to 4 Btu/ f t2 per heat ing degree day are common. This ra t eis comparable wi th o ther energy-effic ien t approaches such as superinsula ted an d passivesolar const ruct ions and m uch b et ter than t rad i t ional above-grade Const ruction wi th atherm al in tegri ty fac tor in the r ange of 10 to 12 Btu/ f t2 per heat ing degree day .Earth-shel tered houses , as a passive means to conserve energy, perform significantlybet ter in some c l imat ic reg ions than in o thers .Earth-shel tered houses are not the opt imum passive concept in severa l major housinggrowth regions of the country.Earth-shel tered houses , inc luding the i r land and s i te improvements , will cost anest imated 10 to 35% more than comparable aboveground houses , and th is ad di t ional costm a y no t he jus t i f ied on a life cycle cost basis, given 1981 m ar ke t conditions.The use of earth shel ter ing wi ll p robably grow in som e parts of the count ry ; however,broad-scale national or regional ut i l izat ion is not l ikely to occur in the next 20 to 30years.


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EARTH-SHELTERED HOUSING,AN EVALUATION OF ENERGY-CONSERVATION POTENTIAL

INTRODUCTIONIn te res t in the use of ea r th-shel tered hous ing has increased markedly over the p as t f ew

years. Since the mid- l970s , a major reason for cons ider ing ear th shel ter ing has been i tspotential to conserve energy, which has been claimed to be as high as 80% or more whencompared to traditional, non-energy-conscious, aboveground houses. This conservationpotent ial and increased public in te res t , juxtaposed with numerous unce r taint ies , such as theconcepts actual energy performance and cost to build, led to the necessity of th is repor t .The repor t inves t igates the energy conservation potent ial as well as the po ten t ia l for broad-scale ut i l izat ion throughout the IJni ted States . It is based upon act ivi t ies under taken by theITS. Department of Energys (DOE) Innovat ive Structures Program (ISP), bo th a t the OakRidge National Laboratory (ORNL) and through subcontractors , as well as the publ ishedwork of a nuniber of exper ts i n the area . I t uses the methodology developed by the IS? inits overall approach to the evaluation of earth-sheltered housing, discusses the activities oft h e ISP in ear th she l ter ing , and shows the relat ion of these act ivi t ies to the overal l analys is.Final ly , i t draws some conclus ions regarding the fu ture potent ial of thi s concept.


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EARTH-SHELTERED HOUSINGScope

The focus of th is repor t i s on ear th-shel tered hous ing rather than on ear th-shel teredbuildings in general. Commercial, insti tution al, and industrial s tructu res have beenexcluded because nonresidential s tructures are built below-grade primarily in response toissues other th an energy conservation. Exam ples of these issues are the preservation ofopen space, the high value of a particularly desirable location, o r s torm protect ion (as inOklahoma schools) . I n addition, a wide disparity between the physical requirements of com-mercial, industrial , and residential space inhibits transfer of research between these build-ing uses. I t was decided to focus attention on the housing sector where energy Conservationis a major issue and, for the purpose of thi s evaluation, to exclude the othe rs. This decisionwas not meant to imply that s ignif icant energy conservat ion, through ear th shel ter ing, can-not be obtained in commercial, industria l , and ins ti tutiona l facil i ties . Clearly i t can, andthis m a y be a f rui t fu l area for future evaluat ion.

High-density or niultifamily residential housing was also not investigated in depthbecause the successful application of the ear th-shel tered concept to these areas dependsheavily on neighborhood design and community planning issues which were beyond thescope of the ISP. This area, however , appears par t icular ly promis ing as energy conservationcan accrue f rom hoth improved bui lding perhrmance and a s ignif icant reduct ion in t ran-spor tat ion, ut i li ty d is t r ibut ion, and embodied energy consumption resul t ing f rom the higherdensity.

Descrigtion of Earth-Sheltered Housing*Numerous publications exiti t which amply describe both the concept of earth-sheltered

hous ing and the s ta te of the a r t . Some of the more ins t ruct ive documents are avai lablefrom sources l is ted in the section of this report entit led ADDITIONAL SOURCES OFINFORMATTON. However , s ince this repor t may be read by persons unfamil iar wi th theconcept, a very basic description follows.

Ea r th she l te r ing uses the ea r th as both a moderator and a harr ier . The ear th provides anmre s table and moderate environment in which to place s t ructures than does the atmo-sphere. I t also provides a barrier to wind and s t arm effects and a large t h e r m a l s t o ra g ecapaci ty tha t a l lows inte rmit tant e nergy sources , such as the sun, to be used effectively.

* In fo rma t ion in th i s and the fol lowing se ct ion has heen borrowed liberally f rom Eartlr Sheltered Hoicsrng Code,Zwatng, and ImasctrLy Zssws, prepa red for thc IJ S. D e p a r t m e n t of Hous ing and Urban Development by t h eUnderg round Space Center, Universi ty of Minneso ta Used with permission.

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Ea rth- she ltere d housing varies widely in design and layout. Typical relat ionships to theground surface are shown in Fig. 1. Some residences have only earth-covered walls; forothers, earth also covers the roof. Most types can be const ruc t ed a t t he na tu ra l g rade .

One of the most common types of earth-sheltered housing is the elevational design(Fig. 2) in which windows and openings are grouped on one side of the structu re. Thethree remaining walls are earth-covered . When the windows face south , a maxin iumamou nt of passive solar heating can be obtained. Those mom s used most freq uen tly dur ingdaylight ho urs a re usually placed along the wiiidoiv wall.

earth-cowered walls only

earth-covered w a l k and rooffu Ily recessed *

Pig. 1. Typical relationships to the groiinall surface.Another common type i s the a t r ium design (Fig . 3). In th is design , the habi tab le rooms

cluster around the a t r ium or courtyard to provide exter ior exposure . Atr iu m designs ar emost commonly used on flat si tes or on those surrounde d by intense developmeiit.Other ear th-shel tere d dwel lings have windows on m ore tha n one wall and begin to more

closely resemble a tradit ional house plan than ei ther the elevational or atrium designs(Fig. 4). These designs are best in milder cl iniates where the impact of cold winter windsand hot summe r af ternoon s u n will no t significantly reduce overall energy perform ance.

Many earth- shel tered res idences perform well f ro m a n energy conservation poin t of view.The level to which they perform varies with th e specifics of the ir design. The rang e of the iractual energy performance wil l be discussed in the section enti t led GVALUATION OF T H ECONCEPT.

Factors InPluemmcing Energy PerformanceOne s igni f icant advan tage of ear th-sh el tered housing and the reason for ISP evaluation

is i ts potential energy savings when compared to tradit ional aboveground housing. Thispotential is based on several unique physical characterist ics.

The first is the reduction of heat loss due to conduction through the building envelope.The amount of heat lost in th is m ann er i s a funct ion of th e the rm al t ransm ission coeff ic ien t


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floor plan

sectionFig. 2. Elevationai design.

8 R R l l - O W G 81-4799

I

floor pian

sectionFig. 3. Atrium design.


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Fig. 4. Earth-sheltered house with a more traditional plan.(%factor) of th e envelope and t he te mp era tur e difference hetween the inside of th e envelopeand the outs ide . Whi le the R-fac tor for ear th i s substant ia l ly lower than t ha t of o ther insu-lat ir ig m ateria l s , the lar ge amount of ea r th inherent in ea rth s hel ter ing can provide anoverall R-factor com parable with more highly insulated structures.

The temperature d i fferent ia l for aboveground s t ructures is the difference between theoutside a i r tempera ture and th e in ter ior tem pera ture main ta ined for the comfort of its i nha -bitan t . Under extreme conditions, this differential can be as much as 32C (90F) or morein some par ts of the country. The daily and seasonal fluctuations of tem per atu re below t hesurface of the ground never equal those of the air above. The deepe r t he t empera tu re istaken, the less severe will be the variat ion. This concept, i l l l istrated in Figs. 5 arid 6 ,shows the dai ly and yearly so i l temperature f luc tuat ions at various depths. Th is reducedt empe rature d i fferent ial r esu l t s from th e ther ma l s torage capabi l it ies of th e soil whichmoderate extrem es of temp eratu re arid create seasonal lags, wherein energy f r s m one seasonis t ransferred to the next season.


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QRNL-DWG 81-4813

TEMPERATURE (OC 3Pig. 5. Daily temperature fluctuation.

wII:a:a.Ew

t 0a-40

-20

Fig,

-90- 40

ORNL-DWG 81- 48144030

MINIMUM AIR T E M P E R M U R E

AUG OCT OEC FEB A P R J U N AUG6. Annual temperature fluctuation (Minneapolis).

Figure 5 shows that da i ly f luc tuat ions are v i r tua l ly e l iminated a t depths us shal low as0.2 m (0.7 ft,) o f so il . At grea ter depths , soil t emperatures respond only to seasonal changes,and the change occurs aft er considerable delay. Figure 6 shows the seasonal temperaturefluctuation at various depths in the Minneapolis-St . Paul area. A t a depth o f 5 to 8 m (16 to27 f t ) , the ground temperature is vir tual ly constant . In addit ion to the dam ping effec t, therei s also a s igni f icant thermal lag effect which occurs at depths below 3 m (11 f t ) . A t t h i sdepth , the so il ten ipera ture lags behind the surface temperature . This effec t can carry someof the stored coolness of winter in to summer and some of t he s t o red hea t of sunimer in towinter . Few resident ia l bui ld ings are bui lt to a depth to t ake ful l advantage of t h i sphenomenon.


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T he th ick ea r then b lanke t a round much of an ear th -shel te red dwell ing effectively el im-inates inf i l tra t ion through those por t ions covered. This reduces energy loss due to in f i l t r a -tion to only the exposed portions of the s t ruc tu re . Whi le th i s loss of inf i l t ra t ion m a yrequire th e ins tal la t ion of a vent i la t ing sys tem to main tain indoor air qual i ty , these sys tem scan be readily designed to recover a l a rge portion of the energy normally lost when ventila-tion b y infiltration is utilized.

Many ear t h-shel tered dwellings are cons tructed of concrete or concrete block, which hasa large therm al s torage capaci ty . In addi t ion, under cer tain circumstances , the ea r th aroundport ions of the s t ruc ture can be th erma lly coupled to the bui lding wall so t h a t t h e s t o r a g ecapacity is s ignif icant ly increased. This the rma l s torage capaci ty can absorb excess energyfrom the ai r or from direct solar insolat ion. This heat is released back into the dwellingwhenever the ins ide air. tem per atur e is below tha t of th e therm al mass This process can bes low enough to ca rry a house for several da ys should th e energy source be interr upted .An example of this effect is shown in Fig. 7. The thermal s torage capaci ty can also beintegrated with energy sys tems ( f i replaces , wood stoves, passive solar, etc.) which provideheat. on a f luctuat ing bas is . This in tegra t ion can effectively dampen th e f luctuat io ns andthereby provide a greater degree of overall comfort.With proper des ign, the effects of these phys ical charac ter is t ics can resu l t in a signifi-can t reduct ion i n both h eat in g and cooling energy requirements .

In addition to the potent ial energy savings descr ibed above, there are several o ther fac-to r s that indirect ly ineduce energy consumption an d thereby enhance the viabil i ty of t h eearth-sheltered dwellings concept.

With the development of clusters or neighborhoods of ear th-shpl tered houses , ear thberms and ear th-covered roofs can create a far less bui l t -up appearance than t radi t ionaldevelopment. This factor , p lus the potent ial use of f la t ear th-covered roofs as open space,would al low ear th-s hel tere d hous ing to be bui l t to higher dens i t ies , th a t is, more dwell ing

OR N L- D W G 81 -48102 0 7 i m - . - 1 I I I I I I PO

Fig. 7. Temperature stability of an earth-sheltered house (Rolla, Missouri).


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uni ts per land area, than t radi t ional s inglc- family, aboveground hous ing, wi thout loss ofarncni ties . The potent ial increase in dens i ty and the ut i l izat ion of marginal lands wi thina n urban or suburban area could reduce the total energy consumption of the community hyshor tening t ranspo r tat ion and ut i l i ty dis tr ibut ion dis tances . Marginal lands are thosewhich, because of proximity to var ious other community funct ions such a s heavy indus try,t r ans i t corridors, and ai rpor ts , arc normal ly cons idered inappropr iate for t radi t ionalresiden tial developrnent. The sound and visual isolation potential of ear th-shel tered hous ingcould al low some of these marginal lands to be considered fo r residentia l developmen t, whilesome reduction in the em bodied energy of a comm unitys physical s tru ctu re could occurl h r o u g h the developme nt of m ore efficient road an d util i ty systems. Wh ether t his would beoffset, by the higher embodied energy of mater ials normal ly associated wi th ear th-shel teredconstruction is uncer tain .

Final ly , proper ly des igned s t ructures that are subs tant ial ly surrounded and covcred byear th can be inl ierently protected f rom many weather ing influences that cause deter iora-l iun . This slowing 01 deter iorat ion reduces the energy consumed in the m aintenance of t h es t ructure.


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EVALUATION OF THE CONCEPT

Energy PerformanceBackground

The init ial effort in the evaluation of energy conservation in earth-sheltered housing wasan at tempt to determine the energy performance of these dwellings. Cur ren t ir iformationabout this performance and a comparison of i t with other types of hous ing has been com-piled from claimed, calculated, and monitored energy performanc es. Claimed performanceis typified by such phrases as My earth-sheltered house uses 60% l e s s energy than tha tused by a tradition al above-grade dwelling. Calculating the energy performance util izesthe various modeling toots available to the building designer. Th e final approach is to f ieldmeasure an inhabited dwellings actual energy performance.(Ilaimed performance

This approach is the leas t scient i f ic and the most prevalent method of descr ibing theactual energy performance. The popular press and descriptive brochures on earth-shelteredhouses have most frequently carried claims of heating and cooling energy savings of up to75% over conventional aboveground houses. Claims also tak e other fo rms - or example,We burned only 1 3 / 4 cords of wood dur ing th e las t heat ing season,n or My heating billsfor December and Janu ary were on ly $45 to 50 ot bad The more radical claims suggestthat energy savings as high as 90 can be expected, while the more conservative claimsexpect savings o l around 50 to 60 .

Although all of these claims are interes t ing and cer tainly get peoples at tent jon, theyhave a fundamental problem. They offer no basis for true comparison. They represe nt awide variety of earth-sheltered housing types, climatic regions, s izes of s t ructure, comfor tranges, and lifestyles. In most cases, the trad itional above-grade house comp arison isrnade with a poorly insulated fr am e house which ha s received no weatherization Improve-ments, in shor t , wi th a type of house that is no longer built.The poten tial inaccurac ies of this ap proach, coupled with the lack of accurate knowledgeof the actual energy performance of various types of housing and the many significantirnprovements, such as increased insulat ion, improved weather s t r ipping, and mul t ipaneglass , that are being appl ied to current ly cons trueted hous ing severely ehdknge the credi ta-bility of these claims . Wh at is needed is a more objective, analytical approach, which canrespond to the shift ing base of compar ison, and a multitude of differing design and con-s t ruct ion features . A calculated performance (if accurate) and a. monitored performance (ifrepresentative) can fulfiIl th is need.

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Calculated performanceThis approach usss various analytic models available to tlw bui ld ing designer f or calcu-

lati i ig the energy consumed by a building based on a theoretical design year for various cli-mates . This approach e l iminates many of t h e sulajective factors a n d provides a more objective comparison of various designs and concepts. Earth-s heltere d acrd abovegrouad housesa r e rion compared on the same set of assumptions. Only the s tructur~ nd the t empera tu rearound the structure are var iables .The calculated pe rformanre for f ive di f ferent locat ions in th c Uni ted S tate s is shown iaTable 1. For compar ison, t h e performance of the same size ~f house, built above-grade togood energy conservation statndards for 1980, was also calcu latcd The specific design:: ofthe two houses (one ear th-shel tered and one above-grade) are i l lus t rated i n Figs 8-11 (seeref. 1).

Table 1. C Q ~ I I ~ ~ ~ ~ S O ~ If the calculated anrriral energy performance ( i r ~-,?ilJionsQf Btu) for earth-sheltered and ~lbovc-grade esidences in five citiesCooling

BLAkSY SOLEST BLAST SOLEST BLAST SOLEST.................. .................... ............ .....................

Total Tota l.......... . . .Type of ......H e a t i n gresidence sav ings~ ................. ~ ~~ .

B o s t o nEa rth -sh elte red 26.7 16.3 3.6 1.0 30.3 17.3 15.7Abov e-grade 30.0 3.0 33.0Conv entional (ne w) 83.8 9.6 93.4

Ear th - she l t e red 3.7 0.0 5.7 9.9 9.4 9.9 4.9A bow-grade 5.2 9.6 14.8Conventional ( n e w ) 25.7 55.8 81.5

HOUStQi l

KnoxvilleEar th - she l t e red 13.4 5.7 2.2 6.6 15.6 12.3 10.0Above-grade 12.5 12.8 25.3Conventional (new) 60.8 30.0 90.8

MinneapolisEar th - she l t e red 49.4 35.3 5.3 1.7 54.7 37.0 34.7Above-grade 67.1 4.6 71.7Conv entional (nev;) 92.4 9.4 101.8Conventional (older) 172.0 12.0 l8l.O

Ear th - she l t e red 27.9 14.6 3.8 0.0 31.7 14.6 20.0A h o v e - g r d e 24.3 10.3 31.6Conrentior ia l (new) 85.0 18.5 103.5

Salt Lake City

Percen tageof energysav ings

48

33

52

49

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Hea t ing and cooling loads were calculated for both the aboveground and the earth-sheltered sfruetureu, using BLAST with the new PLATO f ron t end. I,oads fo r t he ea r th -sheltered structures were also calculated wi th SOLEEST by Davis Alternative TechnologyAs s o c ia tm (DATA). D A T A also provided an estiniatc. of energy loads for cotiventional andold s t ructures of the same s ize in the s tudied reg ions.

Ths RI,AST program has been widely accepted and thoroughly debugged fur conventionals t ructurcs . Because the data inpu t was standard , the resu l t s a re acceptable . The BLASTprogram, however, ha s l imi ta t ions in the codes for s imula t ion of massive s t ructures . Thepr.rgram does not recognize many passive heat ing fea ture s and earth- shel ter ing characlcr i s-~ i c s , o an exIrapolation was employed t u overcome these ~h o n . t co min g s For this reason, ane n c r ~ ~xialysis f rom DATA was obtained which s imu la t e s earth-shcl-tered and passivestrsrclures in a mole acecgt:hle maiin~r.Thp SOLEST prog ram has i t s slnortcoininigs in t h a tt he analyris is not an hour l y t i rnr-step scheduling analysis for infi l t rat ion, orcupancy, light-i n g anid equipment; instead, i t uses coribtarit average values for these parameters . P t can,l-luil-ever, estimate t he t he rma l mass and the g round t empera tu re s su r rouad ing t he ~ t r u c -tures as was ~alled.or in the designs.

Fable 1 s h o w s Iha t t he hea t i ng and cooling loads for the earth-sheltered structures weregenerally l u v ~ e rn t h r SOLEST calculations. Recausc of this fac t a n d the higher confidencein t h e rlcciiracy of t h calculat ions in SOLEST, t h e SOLEST d a t a was aiseci tcr represent theea r th -sEacltered houses The BLAST data was used to represent t h e above-grade houses i nt he life cycles cost study (described in the subsection enti t led Life Cycle Cos t)

The calculated energy reductions for space eonditiuaiing of an earth-shel tered house, inco111paris~nwiLh ati energy-conserving above-grade structure, range rum 34.7 X IO6 Btuin ~ i n n e a p o l i s~ 4.9 x 10 Btu i n Houston. he percentage reduction ranges f rom 58%in Salt L:tke Ci ty to 33% in Houston. These com parisons util ize the U L I S T calculat ion forabovc -grade s l ructures and the SOLEST calceilat icsn f or earth -she ltered struc tures .Other i:akulations of energy reductions for space condit ioning have been made forwrth-cbeltered houses. These reductions, which tend to be s o m e w h a t grea t e r t h a n thoseintlicated ahh;ve, a r e f r q u e n t l y b a se d on t s tandard average heat loss/gain r a w r a t h e r t h a na spcci fic evniparable design.

Ckl l~.ulated erformance, while providing a bet ter coxnparison between coiieevts, does havelimits. vE711ilr. abovrg;lv.ud t empera tu re da t a is available fo r m a n y Ior:jtjons, relatively l i t t led a t a ex is ts frir ground tm~pxatiiries t various depths w i t h i n the ear th This lack of d a t acan nzpact the accuracy of the various model rng program s The program s awrrent ly avajl-a b l t ~ re limited, as c h c r i b e d earl ier, in lhe i r abi l i ty to accura te ly portray the effect of thelarge , ~ m n u n l f therinal ~nassnherent in most ear th-s helte red building s Tn addition , soilrnoistuw can significantly increase the heat loss of the earth-shel tered s t ructure . Th i s vari-d ~ l es not considered i n the models. More validatio n of the models, plus development of thea19ilily to address thermal mass and soil moistur e, wil l be needed before the calculated per-nr:rinaaicc will I-rr a highly accurate indication of the ac tual energy per for rnnace .


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14

R NL-DZNC 81-9854

Fig. 8. Rendering of above-grade laonse in ~ ~ ~ ~ ~innesota.

Fig. 9. Floor plans for above-grade house: a) op floor; b) hasieane~t evel.


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5

URNL DWG 81-9653

Fig. 10. Rendering of earth-sheltered house in Minneapolis, Minnesota,

Measured performanceFor the informat ion obta ined by measuring the energy performance l o be most ustmful, it

should be expressed in units which al low a di rec t comparison am ong various housing types ,s izes, an d heat ing , vent i la t ing , and a i r- condi t ioning systems as wel l as various cl imatic con-dit ions. One such method of com parison curren tly in use is known as t he T he rma l In t eg r i tyFactor (TIF). I t ref lec ts the Btu / f t2 per degree day to provide space condi tioning .

Figure 12, prepared by the Lawrence Berkeley Laboratory , shows the range of TliFa furvarious c lasses of aboveground housesd Th e Mast in h ~ u s e t 2.3 and the BrowneI1 house at3.0 are two innovative aboveground structures that were monitored by the HraokhavenNational Laboratory.Only a handful of earth-sheltered houses have been monitored in s uc h a m a n n e r t h a t t h eTIF can be accurately identified. One house located near R apid City, South Dakota , wasmonitored during 1978 and 1979.' It consumed about 28,000 Btu/ f t2 for 8144 heating degreedays, which yields a TIF of 3.5 Btu /ft2 per heating degree day. The repor t on th is housewent on to note t ha t typica l aboveground fr am e construct ion homes in t he same locationgenerally require 10 to 12 Btu/ f t2 per heat ing degree day .

The energy performance of five earth-sheltered houses is currently being monitored aspar t o f t he Minnesot a Hous ing F inance Agency Dem ons t rat i on P r o g ra ~ n .~ eve ra l of t hehouses have been monitored since June 1980; others were not begun unti l November 1980.Based an t he l imi t ed da t a acqu i red t hus fa r , t he TIF appears to range f rom abou t 0.8 tosl ightly over 3.0 Btu/ f t2 per heat ing degree day . Table 2 reflects various TIFs fo r t heperiod between September 1'380 and Feb rua ry 1981.

Another earth-shel tered house in suburbai l Minneapol i s i s being monitored Based ont h e d a t a f r o m J u n e 1979 th rough January 1980, the TIF was found to be 1.02. How ever, aTIF of 1.6 or 1.7 is expected when the house completes a full ann ual cycle. Typical TIFs forconventional houses in th is location were between 4 and 15.4


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(P1

1 ...______._........1'0'

( b )

Fig. 11. Floor plans for earth-sheltered house: a) op floor; b) basenneait level.


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20 8 16 I 4

975 75 B U I L D I N GPRACTICE N A M B ) c c ~r

STANDARD (19791-----,OQO 4,000 5,000 6,000 7,QOO 8,000 9 2 0 0 D 40,000

FAHRENHEIT DEGREE D A Y S (BASE 65*F)

Some monitoring through t h e r ~ s d i n g f electric me te rs has also heen accomplished i nvarious parts of t h e country. In one s tudy, f ive earth-shel tcred Oklahomn houses were mon-iloretl between 1917 and 1978. U n f ( ~ ~ t u n a l e I y ,he energy consumption recorded includedappliance usage arid domestic hot w:itw heat ing as well as the energy expended for spaceheat ing and cooling. This fac t makes i t ext remely diff icult to factor ou t lifesty le differetices;therefnr r , the results are diff icult to compare quanti ta t ively . Figure 13 i l lustrates theenergy ~ J ~ ~ f O r l ^ i a l l C ef t he five earth-sheltered houses. Figure 14 compares the nionth lytotal cnergy usage in convent iona l aboveground an d cw-th-sheltered houses. Theahovegrouncl consiin1ptioi-t i s based 11 the mean usage of 20 randonily selected, all-eler trie


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18Table 2. Monthly thermal integrity factor for five Minnesota

earth-sheltered residences........

J u n e July Aug. Sept. Oct. Nov. Dee. J a n . Feb.1980 1980 1980 1980 1980 1980 1980 1981 1981Burnsville n a a 0.65 0.84 a a a 2.03Carnden 0Seward 0 0 0 0 0 2.14 3.60 2.53 3.19Wild River 0 0 0 0 0.19 2.05 1.08 0.91 1.27

i Iouse. . . . ~ .__..____

0.89 1.20 2.66 1.92 a0 0

Willmar I a 2.28 2.34 1.23 2.72 2.01 a~

N o d a t a taken.

3T

25; 3

L ... 1 r 1 1 ....I... I I l . . .A 22UN JUL AUG SEP OCT NOV BEC JAN FEB MAR APR MAYENERGY CONSUMPTION FOR FIVE OKLAHOMA MOUSES

Fig. 13. Msntbly energy usage ia7i f ive earth-sheltered

bk t

L-I L-.LUJ 1JUN JUL AUG SEP O C T FdOV DEC JAN FEE WAR APR MAY

AVERAGE ENERGY CONSUMPTION : EARTH SHELTERED vs ABOVEGROUNDFig. 14. C~mplai-is~nf monthly total energy usage in c ~ n v ~ ~ t ~ ~ ~ a ~bovegrsund and earth-

sheltered homes.


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dwell ings in the cent ra l Oklahoma area . This approach compared the earth-shel teredhouses to aboveground houses, which may or may not have been buil t with conservation inmind. A cornparism wi th recently buil t , energy-efficient , above-grade houses would prob-ably have reduced the diff erential in energy consum ption. However, in both cases, ea rth -sheltere d houses would have consumed less energy. Oth er isolated examp les of measuredperformance are undoubtedly occurr ing in other regions, a l though, to date , no resu l t s fromthese ac tivi t ies have come t o the a t ten t ion of t he au tho r .Evaluation ta, date

Based on the l imi ted informat ion gathered to date , i t can be sa id tha t ear th-shel teredhouses can perfor m significantly bette r than tra dit ion al ahove-grade dwellings. The claimth at heat ing energy consumpt ion can bc reduced 75% appears to be substant ia ted when oneccrrnpares a well-designed, earth-sheltered house having a calculated or monitored TIF of 2.5wi th a t rad i t ion al house having a TIF of 10. Because the intuit ive claimed performance, thecalcula ted performance, and the moni tored performance a re in the s ame rang e, the probabledegree of conservat ion tha t can be obta ined through earth shel ter ing is believable. How-ever. , earth -she ltere d housing is not compet ing wi th the t rad i t ional dwel ling, but ra the r wi thcur rvnt home-building practice and with oth er fo rm s of innovative, energy-conserving hous-ing. The TIF of these s t ructu res d i ffers markedly from t ha t of the t rad i t iona l house . A TIFof 7.5 is considered as representa t ive of a baseline, moderately insulated h o ~ s e . ~ig-ure 12 shows the Nat ional Associa t ion of Hom e Builders 1975/1976 Building Practice rang-ing f rom 5.8 to 6.2, Values in the 0.6 to 1.1 range are predic ted for superinsula ted h o u ~ e s . ~From th is informat ion , i t appe ars t ha t ear th-she l tered housing does have s t rong conipeti t ionfrom superinsula ted houses in the area of energy conservation . Whe ther or not home buyerswill choose a n ear th-shel tered house or some o ther type of housing as a means to conserveenergy will undoubtedly depend OD inany factors (which are discussed in the following see-t ions).Further work

I t appears tha t the n ieaaured energy usage of a handful of earth-sheltered residencesmay not be sufficient to accurate ly portray th e energy perform ance of this concept. In addi-tion, niost of the monitored houses have been professionally designed with the intent tominimize energy consum ption. Fo r these reasons, a broader moni toring efforl , covering avarie ty of climatic regions and both professionally and nonprofessionally designed houses,could produce s igni f icant ly more usefu l informat ion and enhance the ab i l i ty to furtherevalurite the concept. Work to improve the ca lcula ted performance through t he use of coni-puter. models could also benefi t f rom th is da ta as a means of verifying or improving exis t ingcodes. The resul ts of this extended monitoring should be publicized in conjunction wi th th eresul t s from a varie ty of other energy-efficient housing concepts so t h a t t h e public will beable to immedia te ly gra sp the re la t ive advantages or d isadvantages of each c o n c t ~ t .

Another poorly documented variable is t he impac t of the inhabi tan t s l i fes ty le on theenergy performance of the house. Dwell ings tha t house two working adults who keep the


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20

tempera turc of the unoccupied s t r u c t u r e a t 12C (55F) in the winter wil l undoubtedly coil-s u m e significantly less energy than the same dwell ing that houses a family of siA where t het empera tu re is m a i n t a i r d a t 18C (65F) and wh er e f i en? opening and closing of t h eehtcrior door by the children is e a p e c t ~ d It has also been suggested that some pz-i~plewhomove into houses which are classed as energ:y conserving nctually change their l i festyles toeri l iance the effect of the structure. ive solar duell ingsWhether or not this addit ional energy savings, achieved through a change in l ifestyle, houldbe universally applicable has i ~ o t een determiilecl It is, therefore, with a seme 3f someuncertainty that one must view the actual eiiei gy performame of earth-sh el tered houses .

This i s pa l t icu lar ly t rue of I,

Applicability o f the ConceptBackground

To assess the overa l l energy impact resu l t ing f rom the optimum uti l izat ion of ear th -sheltered housing, i t is necessary to detei inine i o what extent this concept can be prudentlyapplicd throiighout the United States, i i iat is, to understand the fa c tors th a t i rl fluence theapplicabil i ty of earth-sheltered I IOUSPS Earth-shel tered houses achieve the i r energy-conse iving performaace through the use of inher eiil archi tec tura l festui ea si~ch s beingbelow-grade, having massive construction, etc. These passive measures are sensi t ive toclimatic condit ioi is . In fact , the cl imatic ConCiiLioi1 is the domil lan t fac tor in de t e rmin ing t owhat ex tent an ea r th -she l t e red house is the a pprop ria te response to t h e h o ~ a e o ~ , v ~ i e r sesireto minimize eflergy consumption.

Ihese houses also have certa in unique physical cha racter i s t ics which are impacted bytopography, subgrade condi tions, and o ther fac tors t ha t call liiilit t he cost. effective applica-tion of th e concept in certa in locations. She added costs, arcrwd f r o m responding to thesevarious factors, teiid to inhibit, but iiol el iminaie , t he application of t he concept. In general ,these factors haw l i t t l e or no impact on the dwel ings energy p~ sf or m an ceDemographic factors such a s the type , size, and location of housing units be ing buil t ,a long wi th current popula t ion and growth t rends, ass i s t in delcrmining t h t > d p p l i m b i l i t ~ fthc earth-sheltered approdch.

-

Earth-she tercd houscs arc able to sigii ificantly reduce the energy consutned irl iient ingand cooling through the use of various inherent elements of the ir design. These i n d u d e ai1eartheii blanket over 211ci around t h e structurr- to red nre infi l t rat ion, close coupling to deepground t e m g r r a t u r e s to minimize the temperature differential betweoii indoors and the sur-roundings, liiriited openhg i n t he enbelope, so lar-wiented windows to permi t passive solarheating, heavy masonrl corisil uctioii to perinii t h e s t o r a p of solar


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Table .% Twenty-nine cit ies investigated ira a regional analysis o fground and abovegrvuaid climates

Minneapoli.i, MinnesotaNnsh s i lk , TennessecNew Ori rans , LoiuisianaNew P o r k City. New icirkOhlahotnil City, 0kl;ihorraPhoenix, ArizonaRaleigh, North Carol inaSslt Laiw City, U t a hSan Anton io , 'rcxasSan Fsani:isco, CaliforniaSeattle, W&ingStor,Til(;z;t>n, Ar-izo~it iWindsor Lacks, ConnecticutIVast:irlgtc,n, 1s.e.

valiic of earth shdtering and is not necessari ly a total measure of the S ~ B C C ~ S Sr fztilure ofthis climatc.-crtntrol concept. Thp surcess or failure of any s t ructur i> lo cc~nserve n e r g ~

tids less upctn wht.eher it is above- or below-grade t h a n upoal lsow it mas d e & q ~ t l orc~sporid o t he cl imate in which it is placed.

A n n th e r climatic fn r to r ( n o t investigated i n ref. 8 ) that influences the enerm perfor-n ~ m c e f e a r th - sh e l t e rd houses is rainfall. Rainfall directly impacts the amount of m&-turi i n and n;loving th rough the top few meters ~f the grcrutld. I t is in th i s depth range that

T h e presence of waber in the soil markedly increases t h e p ~ t e n t i a ls are biiibi


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22.ORNL-DWG 81 m@

E

F

G

H

I

Fig. 15. Earth-tempering regional. suitability summary map.


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23fo r hea t loss in winter by s ignif icantly reducing the soil's insulat ing charar ter is t ics , Flow-ing wat er nex t to a str uc tur e can also carry aw ay heat. These lossps can be offset, I iotveves,by increa sing the building's insulation.

The niagriitude of h e a t loss due to mois tu re in the soil h a s not, to date , beeri well docu-mented. Many of the var iables remain uninves t igated. Despi te th is general lack ofknowledge in the a rea , i t is fel t tha t the im pact of m ois ture in the soi l on the energy perfor-mance (If an ear th-shel tered house is small by compa rison to the in ipact of placing the dwel-ling below-grade. There fore, while arid regions may be best to reduce win terti me hea t lossand wet, regions best in th e surnrner to prornote loss and reduce air condit ioning loads, th i sfactor does not appear to play a key role in tho decision as to whether or no t to buildbelow -grade.Topography

Topography is another factor which can inf luence the appl icabi l i ty of ear th - she l te redhouses. Unlike cl imate, topography ten ds to im pact on a micro or site-specific scale. Slopescan change dramatical ly in shor t d is tances , and this fact precludes drawing a n y regionalconclusions. IIowever, if a region has many s teeply s loped r idges running in anortheae, t/southsvest direction, it may offer the oppor tuni ty for some ideal ear th-shel teredbuilding site s.

While the impact of topography is diff icul t to general ize, cer tain t~pographic eatiarescan enhance the viabi l i ty of th e ear th-sh el tered concept. S i tes tha t are too steeply slopedfur most fo rms of t radi t ional cons truct ion can f requent ly be eas i ly adapted to earth-shel tered houses . On such s i tes , t ra di t ima l cons truct ion requires ei the r massive grading, abasement, or tall piers to provide a horizontal plane on which to bui ld the s t ructure.Ear th-sh el tered houses , on the othe r hand, a re bui l t in to the hi l ls ide or slopepand f r equen tlythis topographic feature reduces the grading requirement normally associated with th ismode of construction (Fig. 16).

South -facing slopes can be utilized effectively to ma ke th e earth-she ltered h o l m a pas-s ive solar s t ructure. North-facing s lopes may be beneficial in area s where the need to coolthe s t ruc tu re is dominant . East- and west- facing s lopes , in gene ral, should be avoided sincethey offer l i t t le winter pass ive solar heat ing benef i t and can be s ignif icant s i i rnrner t imeliabilities9

The cos t of excavat ing, grading, and bui lding foundat ions for t radi t io nal cons truct ion ons lopes is an inhere nt cost in ear th-shel te red houses . This fact makes the ea r th - she l te redapproach somewh at more com peti t ive where hous ing in hi l ly regions is desired.

Because many ea r th-shel tere d houses are below-grade in some por t ions of the s tructure,careful consideration has to be given to the direction a nd am ou nt of site runoff. I lociil flood-ing problenis can easily occur if s i te runoff is no t an in teg ra l . pa r t of the designcon sidera t on. '*Low spots, where flooding can occur periodically, a re also una cceptable to ear th-shcl teredbuildings. Such spots might he cons idered sui table for aboveground s tru ctures if they canbe raised a.bove the maximum expected flood level.


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earth-sheltered eonstruct onFig. i6. ' I 'yp id constructions on sloping terrain.

Topogiaphy can be an asset o r a l iability to earth-sheltpred houses. A careful under-standiiig of topographic impacts and a iwyonsive des ign are required i f the mrth-shel ter eddwelling is to be a s i m e s s .S ~ b g ~ - a c - l ~onditions

Since e ar th shel ter in g implies bui lding 4 i thin the ea r th , subgrade condit ions can becomea major con sideration. These conditions include soil type, presence of rock, level of th ewate r table , and location of undergroun d wat er courses. While not precludiiig th e const rue-tion of an ear th-sh el tered dwelling, m a n y of these conditiolis can have a s ignif icant impar ton the cost of such con struction.

I'he increased cost of mitigating these usually unseen conclitioris freq uen tly can not beoffset by any potent ial energ) savings . I t is, the re fo re , impor tan t tha t the prospec t ivebuilder understand these facto rs before purchasing a site or d eciding to build below-grade."

Sandy soil could pose a prob lem to ea r th she l te r ing in tha t i t m a y require special shor ingdur ing excavation. In addition. this soil can provide for easy movement of groundw ater d ur-ing seasons of the year when the flow of wa ter a djacen t to th e s t r i i r t ure could s ignif icant lyreduce the energp performance by taking beat away f rom the s t ructure. However, as hasbeen mentioned before, the magnitude of the heat loss is small w h e n cornpared to the bene-f i t of building below-grade

Clay soil, which expands and contracts in response to w e t and dry seasons, requires spe-reia1 des ign cons iderations to em w e tha t the s t ruc ture is not damaaed di i r ing these 137c1es.


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OR ML-FSWG 8 1-4800

Fig. 19. Reduction of expansive loads from beraning structitnm om grade.


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~~~~~~~~~~~ trendsThe potent ia l locat ion , e i ther urban , suburban , or rural, affec ts the ~ ~ p ~ i ~ ~f

earth-sheltered residences. A vast majori ty of the earth-shel tered houses bui l t to da te havebeen single-family, detached stru ctur es. In most urban areas of the count ry , th is type ofdwelling is being suppla nted by higher density, mult ifarniiy struc ture s, which consti tuted42% of all housing built in 1980 and 19XIp In t he toy 21) markets: Minnea polis posted 33%multifamily, Chicago posted 59 multifamily, and Seatt le posted 64%) multifamily. ,411three ci t ies are indicated as appropriate cl imates for earth sheltering. The overall 1J.S.average, including rural areas, shows mult ifamily housing between 34 and 41% for t he yea rs1980-84.bq While ea r th she l t e r i ng has the potential of exploit ing i ts earthen roof as usableopen space in i t dense urban development, very few examples of this type have beendeveloped. If earth-s heltered houses ar e to have an impact an urban area developntent,where most of the people live, then mul t i fami ly as well as moderate-density, single-familyuni t s will have to be developed and accepted. While the concept appears very promising, ithas not ye t adequate ly dem onst ra ted i t s appl icabi li ty to urban areas .

Another trend in sonie urban areas is to build to densit ies (dwellings per un i t a rea )above .what ear th s hel ter ing can support Earth-shel tered dwel l ings are l imited to two o rperhaps th ree s tor ies in height because daylight and view are important t iahitabil i ty factors.Th is caliises ea r th sliel eriing to be mow horizontal than vert ical in rarrture. High-rise apa r t -men t s arid condominiums, on t he o the r hand, ar e vert ica l iai na tu re and can easily add uni tsin response to escala t ing land and construetion costs. This t rend wouid have to be reversedif earth-shel tered housing were to be a viable al ternat ive in these urban areas .Sublurban development, in contrast to urban development , has taken the fmrn primari lyo f single-family detached housing. While most exis t ing earth-shel tered omes a r e s i ng l e-fami ly , in many part s of the count ry suburban lots a r e jus t a few fee t bigger. on two sidesthan a t radit ional aboveground house. This s i tua t ion , coupled with zoning ordinancesrequiring miniminm setbacks from the properly l ine, has caused some problems in s i t ingearth-shel tered houses on suburban lotsjs The higher dens i ty developments in which theearth-she1 ered houses could share common party walls, Hike row houses, have genesalXy notbeen acceptable to suburban communities,

This lack of compat ib i l i ty wi th the current densi ty requi rements , in both arban andsuburban locations, tends to make the approach less cornp&,itive cconomicaily. In someurban areas , the lower densi ty potent ia l o f earth-sheltered houses, when compared withhigh-rise construction, increases the per unit land and si te development costs. This meansthat the home buyer gets less house for the same money. In suburban locations where den-si t ies and lot sizes inhibit the development of opt imal earth-shel tered dwellings, these dwel-lings are forced to low density locations. The larger lot sizes of h w dens i ty area3 permi tparch-sheltered houses to be b uilt w it hi n t h e s e tb a c k c r i te r i a. H O W P V ~ ~ ,he added land andsite development costs, again, mean that the homeowner wil l et less house for the samemoney.The density of development in communit ies is continually evolving. As such, it is possi-ble t ha t some urban area s could impose a density l imi t compat ib le wi th e arth shel ter ing in


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28

order to prescrve a sensp of open space. Suburuaa & reas , surcd hy illere2values, could allow the increaFed densities which pe r mi t op 1 c;:rtli-shtlte:LG cons i ruc-tion. T h e evolution takes t ime, ai td i t rriay be mains )years M o t c t2 r i h-aheltercd hoi iwsfit with in th e urb an and suburbai i developtae i it t rends.

been ho i i t iil ru ia l 13:smal l town areas. These areas h a w n s i t he r h i gh - d en s i i j de n d s no1 space iJnitatioiis.Whi le ear th shel ter ing does provide enei-gy-efficicnt rii a1 hl,usiIlg, it :s VI?::?s e e vixrkets-bil i ty of th e Concept) th at th is segm ent of th e h o u s i n r trnarket is ~ o t izre s i p n i f i cau timprovem ents to t he overall energy efficieiicy of the c o i i ~ ~ t r yi j l h:~::d~areas, the communit ies wil l need to evolve zi ther to b w c r u; to Fi ;phcy : .a,ti+~s.A th,,iiqhit appears feasible to incrzase the dclilsities of s n h u s b a o coi;iiii;in;ti


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29

-- 40.60


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with much higher monthly payments . Even the drama tic energy post savings of an ear th-sheltered house will not offset the cos ts of relocating in m a n y casw,.

-What do these (,rends m a n to the ear th-she l tered concept? The population growth i nthe Southwest is a stim ulu s to possible ea rth-sheltered stru ctu res, especially those utilizingpassive solar h w t i n g . H o a ~~v e i ,he l rer iendous growth in t h e Deep South and Southeaqt i sless likely to s t imulate car th shel ter ing in this region s inee the high humidi ty preventsearth shelteriiig alorie f i o m mitigat ing the discomfor t associated with h igh tempera tu res .Ei ther dehumidification or enhanced air flow is imp orta nt in overcoming discomfor t. Otherenergy-eff icicct . passhe approaches may be ~iiore ost-effective in overcoming discomfort,except where hil l1 topography dictates th at a t leas t a portion of the strn ctim beunderground.

T h e s ev er e ~ i i - i t : ? ~arts nf the U ni led S ta tes ; the Pac if ic Nor thwes t and the Rocky Moun-ta in states, where e ar t h she l ter ing performs well, arc, in gm era l , g rowing slowly. A ongt i m e will be reqrairerl before the existing housing stock is replaced and t h e Impact of anychange as a resul t of ear th shel ter ing is significantly felt

The growth i n the suburb s will p iobably p ermit the more cos t-effective, h igher dens i ty ,emtli-sheltered housing IPowever, thcse stroiigkolds of th e single family, detach ed housem a y we ll r es is t t h e t r e d t o w ar d a h ig h e r d m s i t y urhan environment . The lack o f growthin ru ra l arws will not s t imulate a rapid increase in ear th-s hel tere d houses even thoughm o s t are curre nt ly hui l t in rural m a s .

T he shift towards less-expensive forms of housing, reflected in the f ac t tha t mobi lehomes coirslitutP abo ut 10 of the market and i i lu l t ifainily homes ano ther 401390,will inhihi tear th shel ter ing in Ihe forms tha t exis t today. The inher ent higher cost of construction (seeMarketabi l i ty of the Concept) may eventually make e a r t h sheltering a luxury beyond themeans of most pm cspective home buyers.Evaluation to date

I t is clear that the unique b e n d i t s achieved f r o m the use of ear th shel ter ing, as ;e passivemeans to conserve energy in housing, arp pr ima ri ly regional and not universal in nature.8Other passive techniqu es also sh ar e thi s regiunalism. In addition, the applicability ofearth-sheltered housing i s more dependent on such site-specific issues as topography andsubsurface conditiolis thar i are many othe;. appbaches to housing. Current cievclopmenttrends will need to change mat%ed y for e ar th-sh el tered hous ing to reach i ts potent ial .F inal ly , populat ion and growth t rends in t h e UniiPd States generai ly do not coincide withthe area of optimuni utilization of ear th shel ter ing.

IIowever, before onecould clearly define the exact boundaries of that area, a subs tant ial amount of addi t ionalwork wou d he required - for example , fu r ther s tudy of the relation of climate to cnergyperforniance, an in-depth analysis of the s i te- related factors (surfacc and below-surface con-ditions) as they affect the potenit ia l fo r ea r th-she l tered cons truct ion, and a tnuch morethorough ana lysis of th e imp ar t of f n tu r c building t rends as they relate to where ear th-sheltered buildings a re likely to be huilt

These factors sugges t a sornedlat l imited area of applicability.


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The total anlourat of energy saved through the uti l izat ion of earth-shel tered houses isdependent on both the number of dwell ings actriai ly buil t and the energy performance ofindividual s t ructures . The number of earth-sheltered houses buil t will be determined bythe i r a.cceptance in the marketp lace . There ar e severa l key fac tors in determining marketacceptance. These iaclude einotional fac tors , fac tors affec t ing the ease of acquisi t ion, andeconomic factors. Emotional fac tors include such d iverse i tems a s aesthet ics , curb appeal,s t a tu s image, durabi8it,y, habitabil i ty, and the envi ronment crea ted by the dwell ing. Thef;ictors affecting the ease of acquisi t ion include financing, compatibil i ty with building codes,and f inding qualified cont rac tors arid designers. T h e economic factors influencing accep-t ance of the concept are ini t ial costs, operating and maintenance costs, l i fe cycle costs, andth e prospective ~ o ~ e o ~ v n ~ r ~inancial capab il i t ies.

Rieal es t a t e agents and otbers versed in the buying and sell ing of houses have long real-ized the important role th a t en io tional fac tors p lay in the decision to purchase a part icu lardwelling. Once a house fulfi l ls the hasic physical needs thre e bedrooms, two baths, andwith in t he gpneral price range which the buyer can afford), the decision to buy is, in mostcasw, predominantly an emotional one.

The specific emotional factors fal l into three main categories, which include how thepotential buyer relates to himsel f , tha t is, ego, how he relates to a dwell ing, and how herelatm to the l a rger envi ronment. The ego fac tors inc lude th e need for a s t a t u s image. Ahouse can physically represent where a person is or where a person aspi res to be. A large,impressive house si t t ing atop a hil l overlooking the region will be the only way to sa t i sfysome peoples emot ional needs. An earth-shel tered house dug in to the same hillside wouldmake ii much different statement and could relate to other peoples needs.Another ego fac tor is the need to conform versus the need to he different . In most urbanand suburban areas , t he decision to live i n an earth-shel tered house is clearly nonconfor-nrist In rural areas where physiead separation and individualism is a. norm, ea r th she l t e r -ing may riot he considered so different . Judgin g from i;he millions of colonial , tudor,ranch, California Spanish, and French Provincial homes being buil t throughout the count ry ,i t appea rs t ha t fitting n is impor t an t to many A mericans.

(;nrlrr appeal is ano the r ego fac to r but primari ly re la tes to how others ~ i e wh e house.This i s piiart icularIy important when marketing the house since some decisions 10 buy or notto buy are made hefore ewering the door. Tradi t ional houses develop the i r eurb appealf r o m factors which i p i some cases are difficult t o obtain in an earth-shel tered dwelling. Foyexamplle, l par t i rular ly at t rac t ive formal en t ry in to 8 t rad i t ional home n i i g h ~ ave to bect~iriparedwith a shaded, less visible, sunken ent ry in to a n e a r t h shelter W i t h only a fewhundred earth-shel tered houses having been bought and sold to date, i t Is ton er.rily to beable to general ize on the i tems that are important for best curb appeal.


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The buyers emotional relation to the b~;;;ell;ag s ei:~berdieJ ;A his desire for a habi tah lesurrounding Habitability incilides such fac to i s 44 th e ncc: for light coalfo rt, war inih. an da sense of secu rity. If the buye r en-cis;ons a hC?uSe darrk, aark . atilt: da~trp , h e ~ o p ~ ~ L i r i z t 4erron eous description of e:rtli-sheltet ed ironsee, h e is riot likely to ha\ c n p,u;;tive crnictionalresponse to that dweEiag. Th e durabil i ty of a s tr ac tr lr e c ~ r llso be a l l eii1otioii;ll need, rspe-cially for t iose who want to leave their inarb in l i fp oi t l i n ~ h o 1 to sei roots andgrow in a particiilar locatioil. Dunahi li ly can Le one of t he fa c tw s tha t enh ame s the e a r t h -sheltered concept in t he mind of some huye is .

Hot% he buyer desires to re la te h is home to t h e la r gltVirOiiii1eili call also affec t whattype of house to buy. One ext reme o f &is relatiorlshi II be seen in a plist ine -,-.hit- metaland glass geqmetrlc forii1, that is, a house set on a plane of carefully mnllicured l ~ l h n A tthe other extreme could be t h e e a r t h s h e l t e i dug into a rolliily. rwado\*i where wild tlowersand tal l grass dominate the view a id o d ) a mrroi-4 slit of glass and recessed e i i t q * a y giveany evidence that this is the location of a home. T ~ Pi rst extreme embodies a desire todoinitiate and Coiltrol the environnirnt, the second a desire t3 submi t t o and h lenJ wi th theenvironment.

W h i k s o m e % I~ ~ l i t i o n a lbcvc-grade h o u s e s h a w bee0 effective in harmonizing with the eiivi1 oi1lrreni, ~ m s teiid tothe domination and control of the e ~ ~ v i t ~ ~ ~ i f i ~ i i i .r t h shc tcl b, dn the othe i hand, becauseof earthen-covered walls aad roof , tend t o blend more strongly ~ji t t ; hc surroundingenvirontnenl. Based on the number of abovegfound 11ouses, lx. hich are designed to b l e dwith t he i r env i ron inmt , and the alrnost ~ i r x i v e r s ~ lse of somc s n d s c a y materia l to softenat id t i p most houses into t h e 1 irviroameat, i t would be fair to sag that lmt Aine:icansdesire their houses to harmonize with the environnipat . To t h e extc;,k t ha t t h i s fa r t o r is sig-nificant in the mind of the h o m ~ uyer , i t can e:: ianre the earth-shel tered mncept

I h e composite impact of all the emotional fac tors or1 the d e c i ~ i o ~ ~b to w i l c t h r or not tobuy an earth-sheltered house has not b m i srieil:ificallg studied E c w x i l smali-scale studiesof t h e buyer s views of h a b i b b i l i t y of an earth-sheltered hfillse have 1Because refs. 17 alid 18 appear to be based 011 the satrli. survey infvr n ia textremely l imited nuinber of responses (200) and has no t b ~ e i i jupl icated se, a t o t h e rplaces and other t imes, thei should be regarded on:^ a s indicators of peopics responsm andnot as containing definitive information which could be applied broadly

In ref. 17, ail cxpcrimental earth-sheltered home was piese:,ted t u H g ~ o u p f people,9570 of w h o m h a d m v e r seefl an ezxti~-she tered home before. i w o hundred pecgleresponded to t h e qnestioiinairea used h i the s tudy.t ha t t hey wel:: somewhat 1-0 very likely to h i l d an ruiderqraind iiurric In the next fiveyears it11 such real-world issues as obtairiing financinga n d the various cost far tors . Thc xfore , it could be i n fer red t ha t to a laxs. ex:cr)t, ihcy we12respon ding emoiiorially to the dwell ing

I n ref 18, v a r i o u s construction features a n d alterfldt ives cf an earth-sheltered housex e r c presented to a group of consumers. The icspirideilts preferred ILavikIg o - 9 elevation ofthe house exposed rathen iliati having ih e enlite structi iae h i l t i i n & ~ r g n w n ~ l ~here wasstrong support for the addit iot l of skylights over rooms i l l t lw havk of t he house vhe re

Most houses bu ilt tod ay fa l between these ex L emx.

r 1

Over 4cI% of t h c i espodeiThese respondeiits were n o t faced


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Finding a suitable site on which to cons truct an ear th-shel tered dwel l ing can alw be aproblem. Not only mu st the natura l cons t raints such as topography and subsurface condi-tions he dealt, v, i th, hut also code and zoning limitations, as well as aes the t i c in t egra t ionwith the surroundings These cons train ts have helped l imi t the numbcr of ear th-shpl teredhouses built in ur ban a reas

Many people consider f inancing to be the bigg-esl obstacle t o t h e c o n s t r w t i o n of e a r t h -sheltered houses I n a s tudy done for thc D epar tment of Energy i t i 1W9,20 36% (19 persons)eventual ly obtained f inancing on thei r ear th-she l tered housing, but only a f ter experiencingdifficulties at oae or more leiiding insti tutions; 27% (14 perswns) were unable to f inancetheir project; ?5% (13 persons) had no difficulty ob tair i ii ig construction loans an d m ortgages(of t h i s gioup, 8 had t ies to the lender); 8% (4persons) f inanced thei r project wi th pr ivatecapital; 4% (2 persons; had not received a decision a t th e t ime. While some improve menthas occurred since th is s tudy was made, many of the problems assnc;atPd with finaricirigs t i l l exist .

These problems primarily stern from the relative uniqueness of ear th-shel tered homesan3 the psrcspcctive home biiyws inability to effectively cornmunicate the benefits of t h i stype of innovative, energy-conserving home to potential lenders. As a result, the f inancialcomrnuiiitys perception of risk is increased.21 With relatively few ear th-sh elte red lnoniesand even ewer resales of these homes, i t is virtually impossible to determine a n e a r t h -sheltered houses m a r k et va li ir h a s d OD experience. Although various altern ativ e niekhodshave been suggested, these m ~ t b ~ d save not been broadly tested

A s t rong rnarket demand is the must ef fect ive means of overcoming the t rans ient bar-r i e l s Khich s t and in t h e way of acquir ing ear th-she l tered houses . Sar l i a demand wouldincrease the desigo and constructiori expertise, focus attention on zoning laws which inhi-bited t he coricept, and demonstrate a m a rk et fo r th e ~ Q U X S ,h u s easing the problem ofo b h i n i n g l s ans lhus far , th e e ar th-shel tere d home concept has received only good presscoverage and moderate interes t in cer tain pa r ts of the country. With fewer tha n anes t imated PO00 uni ts per year , compared to a total of 1.5 to 2.0 million total nev i initsper year, a s t ro n g m a r k e t d e n a n d h a s n o t beeii demons t r a t ed . Th i s f ac t has caused t ,he bar-riers to earth siie tering to be removed at a much S~O WN C Face.Econnmie factors

Once ernotioiial arid acquisition barriers have been overcome, t h e n costs or ecosnornic f a r -tors beconie a key element of th e decision-making proccss Those factors, in conjunctionwith the prospective home buyers financial capabilities, will detcririiue whether or not apar ticu lar concept will be util ized.

Most home buyers view initial construction costs, as reflected in their monthly mor tgagepayment , as t he dom inan t eesnoink factor. In recent y ears, ope ratin g costs , which at e madeup primarily of utility hills. have become recognized as anothen economic. factor to consider.Maintenance C O S ~ S re hard to predict beyond a relative level and are theefcre not one ofthe major df .cis ion- inf lucncir i~ actors l i f e cycle costs, which factor all nf t h e above withinterest rates, taxes, cost escalations, etc., are complex and hard to apply t o the home buy-ing situation. The satisfaction of the emotional needs embodied in the purchase of a honne


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far outweighs the economic considerations reflecte in a lifrt cycle cost analy sis. Th is is notmeant to imply that this analys is has no role in the evaluation of buildingp, It can play asignificant role in those buildings where cost or r e tu rn on inves tment is the crucial economicEactor . Commercial and indus tr ial s t ructures are examples of such buildings.

Initial. costs. There is not ye t a sufficient body of d at a f rom which to draw def ini t iveconclusions 011 the ini t ia l cons t ruct ion cos ts of earth -shelte red houses.% Based 0x1 the exis t -ing examples, construction costs have most often been higher for earth-sheltered dwellingstha n r rboveground wood f ram e s t ructure s . Mow much higher has been di f f icul t to assess,because few earth-sheltered houses have been directly conlpared in size* loeation, f inishes,and am eni t ies to an aboveground house. The numbers most f requent ly used hy those famil-iar wi th ear th-shel tered hous ing cos ts are about 10% n-fore. Unfor tunately, the extremelylimited sample of earth-sheltered houses to draw nlurrmbers f r o m a n d t h e lack of an objectivecompar ison wi th com parable aboveground s t ructure s makes this number l i t t le mare than a nunsubs tant iated claim.

To gain a clearer picture of the re la tive cost ~ ~ ~ e ~ e n t ~ a l ,h e Oak Ridge N at ional Labora-tory under took a s tudy to develop the various cos ts associated wi th two comparableresidences, one ahove-grade and one earth-sheltered, in f ive different locations in t hecountry. The goal of th is s tudy was to address regions dis t inct ly di f ferent , not only incl imat ic character is t ics but in eons t ruct ion pract ices as well. Based on maps a n d graphsavai lable through the Nat ional Weather Bureau a n d t h e U.S. Census Bureau, all a r e a s i n t h eUni ted Stat es were plot ted for the following characteristics:* heat ing degree days ,

cooling degree da ys,precipitation,humidi ty ,

* sunshine avai labi li ty ,* term ite and infes tat ion probabi l i ty , and* mate r ial decay probabi l i ty .

Five metropol i tan a reas were selected. This selection was based pr imar i ly on the mapsmentioned above; however, population size was also considered. The cit ies ar e Boston, Hous-ton, Knoxville, Minneapolis , and Sal t Lake City.

Once the five cit ies were selected, the foilowing points were addressed:1. Wh at does the market look l ike in the specific regions?2. What house sel ls best in the region and could be classif ied as typical? [This description

W O U P ~ include informat ion on exter ior s tyle , bui lding mater ial , floor plan style (splitlevel vs ranch, for example) , car parking faci l i t ies (carpor t , garage, or none), type offcu.mdatiun, etc.]


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This informat ion was obtained pr imar i ly from:e U.S. De par tm ent of Commerce, Eure au of Census, Ch aracte ristics of New IIousing; a d

HouSing Special Report, courtesy of t he N ationa l Assccistion of IIome Hi:ildPrs, wl i i c ~addresses the issue of w ha t home huyers seek in s ix major markets .

Per t ine nt da ta f rom th e local chanibers of commercc, inel iding real es ta t e rndraxines, werealso used. Census Rureau statis tic s indicated tha t 52 6% of the house-, built are ranch styleand that 1480 f t 2 of main living space is probably equally popu l a r in a l l the regionsfplected in the s tudyincludes basements and garages as th e base. The following inform ation descr i h e s t h e houst.design we a dop ted fo r th e five re, ions:

Boston.garage;

In th i s s tudy , we refer to the 1480 f t 2 of main l iving spa

base on the main f loor , basement level wi th unf inished space and a twc -cai

Houston: base s lab on grade, two-Car garage attached:

Minneapolis: same 3s Boston, a n dKnoxville: base on ma in level, lower level craw l space 2nd two-car ga rage;

Sal t Lake Ci ty: base 011 ma in level, over crawl space with a two-car rarpnr t a t tached.The des ign of the ear th-shel tered and above-gradp s t ructures had ident ical i o v ~ n izes ,

s torage areas , a i d unfinished space for each of th e regions. Natu rally, th e floor plans differin that the ear th-shel tered home has windows facing south only a i d i n t h a t t h e u n t i n i s h dspace is not necessarily a basemen t area, But , for the home buyer, the exter ior of the ~ ~ U S P .t he genera l arrangement, and the finishing materials are iderntiral for each region in h t kthe above- a n d below-grade structures. The d iffe re rnces x e on ly the o ~ i e s i lhit?v?t in theenergy and earth -shelte red aspec ts of th e houses.

Both houses were designed fo r a h igh de gree of eaeagy conservation , bu t neithc: could beclassed high ~erformance/exFerimental n Lonservation featu res. The aboveground houseis comparable to t he b et ter energy-conserving houses built in 1980 an d RS S I J C ~ , osts some-v h a t more ini tia l ly tha n convent ional houses wi th lower pcrfol marrrce

Ten sets of working drawings were prepared. In addition. a l imited spec i f i r a tk~ndocu-ment for each of these sets was prepared to out l ine t h e elements that ale differeii t i n t h eten designs. As s tated before, a l l aspects except the ones inhP:eiit iir the e,artlr-shelteringand energy factors were ident ical for each s et of two hoi~scsn t he f ivc locat ions

These sets of blueprints , along with specifications, were forwarded YO a consulting r t ~hi-tectural engineer ing f i rm which provided a detailed cost analysis . The firm worked closnlywith bui lders in the local i t ies and ref lects not only the di f ferent s t ructural des ipp bb,t alsomater ials and labor cos ts par t icular to each of thcs , weaq

The init ial construction costs developed by t h a t s t ud y are shown in Table I. The init ialcons t ruc t ion cos t s a r e g rea te r than the about 10% f igurp usual ly used for e a r t h -shel tered houses. The numb ers in Table 4 represent i h e es t imate from olriy one source ar,d


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f ~ ~ c c ,e& milengr;rrl as 6 their broad-sca le applicabil i ty. Howe ver, because theywit 3 - r d W ? h q I f > J ~b tw. gh t t w cse of h h o r and rnalerial t akenffs and because thes e two fac tors

wcr3pted unit, cost figures, the di fferent ia l be tween the two concepts is l ikelyw i t h a brwider Xmse of estiniating. I n addit ion, costs in excess of the "aboutv e bcea; cmfi rn i ed i n other prel iminary invest iga t ions (Ralph Johnson,anal Assoeiatron of Home Builder's Research Ffmndstion, Washington, D.C.,

kz thc opanian of Ihc author that the difference between the "ahout 10% anore" and the3 1 f 3 43X mI:catcd i n 'J'akle 4, is a result of the direct comparabil i ty t h i s study achieved"r~ctwceram ~ ~ h - ~ ~ ~ ~ l t e r t x ~rid above-grade dwellings. Figur es 8-11 i l lus t ra te the eompara-

of r;-*ic:r:alI appearance and finishes of both struc ture s in Minneapolis, M innesota.Siaikilar d ~ > ~ i g ~ sere dcvt . , l~pedo r khe four o ther c i t ies s tudied .

m mi il l i l lln ca li t 11).

Esrth-sheltered structure Above-grade structure Additionsl___ cost for--- .L,cic.


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above-grade houses. The relat ive energy savings in dollars, fronn the BRNTA study,' is s h o wnin Table 5.

Savings from reduced cost4 in insurance fa;r earth-sheltered dwellings has occurred insomc ci rcumstances , but has not been llrliversal in its applicability. Recause the bulk ofinsurance premiums covers the costs of small losscs, theft , arid administrat ive costs, i t isunlikely tha t reduct ion in ca tas t rophic loss potential (fire, wind, etc, ) due to earth shel ter ingwili significantly imp act insurance ra tes in the long term

Table 5, Annual fuel costs f o r heating and cooling of an earth-sheltered andabove-grade dwei l ing using an electria:heat pinrap with a coefficient of

performance of 2.0 and the prevailing local electric sates in 1988)Earth-shel tered Above-grades t ruc tu re s t ruc tu re

~ __ __ ._.___... ...Locat,ion

...._____ ____Boston, Mass.Houston, Tex.Knoxville, Tenn.Minneapolis. Miiln.S a l t L a k ~ i ty , Utah

$292.0073.64116.69282 00226.73

$522.0091.09199.05511.00426.42

Maintenance costs. I t has been said tha t ear th-shel tered houses will have much lowermaintenance costs than aboveground dwellings. This statement is t rue if you compare awell-buil t , properly w aterproofed, reinforced-concrete earth-s heltered house with an above-g rade house with wood siding, asphalt shingles, and galvanized gutters and downspouts.However, readily available, but expensive, materials can also give the aboveground housecomparable low m a i n t e n m c e costs. These inelude brick, slate roofitigp nd copper or alumi-n u m gu t t e rs and downspoutq.

In the case of the aboveground hovse, the buyer can choose between higher in i t ia l orhigher maintena nce coats. Earth- sheltere d houses, in genera l , do n o t permit this choice.More durable walls are requi red for s t ructura l reasons. Waterproofing i s far more crucia land, therefo re, given more ca re and better mate rials. The buyer really has no choice. Tocoinpromise could result in structural fai lure or a leaky roof t h a t i s extremely difficult andexpensive to rep air.

In ter ior m ain tenance costs are h ighly subjec t to l i fe style arid the personal desires of t heoccupants. A s such. no im por tant difference is believed to exist between above- and below-grade construction.

L i f e cycle cost. A number of life cycle coht analyses have been done to compare easth-sheltered a nd above-grade Most were done on di fferent se ts of assumptions.

As a n example of how the assu mptio ns can change the r e s d t s , a n e a r t h -sheltered house, assumed to cost $lS,OOO more t h a n a copiventional house,was analyzed fo r several different conditions. Assuming a 9 % in terest ra te ,80% energy savings, and an energy cost escalat ion of 12 per year , the pay-back period (considering mortgage and energy cost only) was 11.2 years .


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Increas ing the energy cos t escalation ra te to 24% per year changed the pay-back period lo 7.2 years . Including an insurance savings of 30 per yearimproved th is tis 5.3 years , and even increas ing the interes t rate to 11.5%didnut prevent the payback period f rom corning in th e f i rs t y ear of ow nershipwhen the proposed Federal Solar Bank Bill incent ives for ear th-shel teredhousing w ere i n ~ l u d e d ~ ~ ~

The ~,Iaove xample shows clear ly how changing assump tions can change the results . Fewof the assumptions, howwer , ref lect the actual market condi t ions in 1986. Typical housingcosts were significantly niore than the lO,W sugges ted, interes t rates ranged Prom 14 toP(i'%;, energy saviogs were typically 60 o r less, and insurance cos ts were not universally30% less. Thc Federal S olar Bank Bill was na t being implemented.

Because of the deviat ion f rom current market condi t ions , the paybacks of f rom one toeleven gears are not val id for 1981. In ano ther ana lys is , t he life cycle costs were comparedusing another set of assumptions and included maintenance and replacement costs(TabIc

Table 6. A comparison of life cycle costs for typical conventionaland rutdeagraundstructures

Conditions Conventional Undergrounds t r u c t u r e s t r u c t u r ePriceDown payrnenlMoregageIn teres t , %Owner's tax bracket, j6Money inf la tion ra te , %Eneigy cost inflation rate, EHousing itiflation ra te , 5Total rriairilerianeecost for 30 y e a r s

$86,500$17,500$69,0009

35F

827.5$11,805

Rased on t h i ~ nalysisPE he underground house costs leas to own than the a ~house after 16 year s on a s t raight dol lar cost basis , and after 20 years on a discounted basis.Chang ing lhe a ssumptions used in this s tudy to more clcm ly reflect 1981 nasrket, eoiiditianlswould s igni f icant ly extend the payback period.

ihnother I i f r cycle cost analysis ,l including maintenance costs , was based on the actualmarket conditions existing in 1980. The resul ts for each Q the f ive cities studied (Table 7)ind icare that h e otal present-value life cycle casts f o r t h e earth-sheltere dmiliws w e r eccmsiatently higher than for nboveground dwellings. This means the payback is beyonid the30-year s s s u w e d life of t he s t ruc tu re . ~~~~t~~~~emnornit- factors were used fo r each of the two designs fo r the same city; however, these for-tors mverc city-specific.

Life cycle cost analyses were run independent ly for each of th e derlgtm


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40Table 7. Total yresent-val .e We cycle costs aseel ou actual estirn~trd

construction cost and 1981 market condition in five sitits~ _ _ _ _ _ _ _ - _ _

Earth-sh el te t ed Above-grades t ruc tu reocation s t ruc tu reBoston, Mass $105,381Houston , Tex. 76,257Knoxville, Tenn. 72,117Minneapolis, Minn. 101,677Salt Lake City, Utah 79,669

$85,42561.11362 36782.40972,527

Fo r each one of th e ci t ies, t h e following informatini i was obta ined:s ta te income tax ,property tax rate (state, ci ty, and county),sales t ax ,median household income per capita,cost of living ind ex,type of mortgage and rates available,eilergy costs (fuel),expected fuel escalat ion rate, andmaintenance cost for th e two different designs for both heating, venti lat ing, and air con-dit ioning and the structure i tself, which included exterior and i i i terior painting cost andfrequency, roofing, carpe ting and o ther flooring, plumbing repairs, electric repairs, appli-ance serv ice and/or rep lacement , appl iances, ha rd w a.~ e , es t cont ro l , a i d miscellaneousitems.The study also tested the sensit ivi ty of the basic construct ion costs to determine whcther

o r not ini t ial costs of 10% more could be economically jixtified by savings in energy andmaintenan ce costs. The results (Table 8) indicate that added base construction costs of asniuch as 10% cnm? might be just ified in Minneapolis and Salt Lake I: i ty, but that costsbelow 10% more ~ o i ~ l dave to be obtained for Boston, IIousion, and Knoxville.

Table 8. Total present-valwe ife cycle costs for RBI R B F D ~ - . T . C ~sseconstruction cost for earth-shrl tered dwellings of 10 more that?

above-grsde and 1980 market conditions in five citiesEarth-shel tered Above-grade

s t ruc tu re s t ruc tu reocationBoston, I l lass. $85,832 foFj5,4.25: louston, Te x. 62,987 61,113Knoxvi l le , Ten n. 63,590 62:367Minneapolis, Min i l . 82,419 82,403Salt Lak e City , Ut ah 71,035 72,.527

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51/62

41Another s tudy compared const ruct ion and opera t ing costs of earth-shel tered and above-

grad e homes in Seatt le , Wash ington; Dallas, Texas; and M adison, Wisconsin.% The res ultsof this study showed that the ten-year cost of ownership for an aboveground house was lessthan for a below-grade house in a l l ci t ies studied.

A newsletter published by a builder of earth -shelte red ho uses included the following:In an earth-shel tered bui ld ing , there i s a poin t which i s ra ther d i ff icu l t tocompute, a t which the building wil l pay for i tself in u t i l i ty savings, ma inte-nance, insurance, etc. Based on an 8 inflat ion, a 10% escalat ion in energyprices , and count less o ther fac tors , th is payback seems to be somewherebetween 20 and 25 years . This will not be easily perceived by those whosevision extends only between their wallet and property l ine, but for the dis-cerning homeowner, these buildings represent one of the best investmentsthat you can makeF5

A five- to t en-year payback period i s probably the maximum length tha t is l ikely to haveany effect on the choice of housing type. The avera ge length of residence in any given homein the Uni ted Sta tes is about five years. Therefore , fo r a buyer to consider potential long-term savings of benefi t to him, i t should occur during his period of occupancy. A five- toten-year period, while not meeting the average, does cover a large port ion of the population.I t i s a l so like ly tha t the durabi l i ty fac tor , which appea ls to man y prospect ive ea rth-sheltered home buyers, would indicate a longer-than-average residency.

A s can be seen from the various results l isted above, a wide d ispari ty ex is t s be tween th evarious l ife cycle cost analyses with payback ranging from 1 t o 30 years or more . Sincethere h as been l i t t le agreemen t on wha t const i tu tes val id assumpt ions to date , th is d ispari tyis l ike ly to cont inue . However, i t i s fa i r ly ev ident th a t ear th-shel tered houses are noteconornically at tract ive (payback in the five- to ten-year range) when the l ife cycle cost isbased on current (1981) market condit ions.

earth sheltered housing an evaluation of energy conservation potential

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