How many more neighborhoods in North America will be devastated before people realize that cookie-cutter ranchers should not be built in tornado and hurricane prone regions?
Popularly called “underground houses” during the 1960’s and early 1970’s, earth-sheltered houses gained a reputation as either being eccentric or “hippyish” by the 1980s. They were promoted by environmentalists in the Carter Administration, several magazines as “Mother Earth News” and famous architects such as Moshe Safdie, but never represented a significant portion of new housing in North America. They were particularly appropriate for the Canadian Prairie Provinces and the Tornado Alleys of the United States, but rarely built in these locations. In fact, they are mainly concentrated in regions of the United States such as the Southern Appalachians, northern California and Vermont, where young adults fled in the 1970s in an attempt “to get back to nature.” Their rise and decline in popularity seemed to have paralleled the use of wood stoves for heating.
An earth shelter house is simply a home that has at least some wall covered by earth berms. The structure may or may not also have a layer of earth or sod on the roof. The home does not have to be in a cave or burrowed deep in the ground like a Prairie Dog town. In fact, the original term, “underground architecture” was quickly dropped in the early 1970s because it projected an image of a windowless, building fit only for gophers.
This architect’s first design of an earth sheltered structure was in 1984 for a neighborhood shopping center on Merrimon Ave. in Asheville, NC. The project also involved the first use in that region of the “new fangled” products, EPDM membrane roofing and high-strength splitface concrete blocks. Initial analysis quickly determined that placing earth on the roof of the shopping center was not cost effective. The initial construction cost of the much heavier roof load could not be absorbed by 20 years of savings on energy costs. In fact, a better insulation value could be obtained at a small fraction of the cost by installed R-36 rigid plastic foam insulation sheets.
There was a BIG surprise when the building was completed. The HVAC system (heating & air conditioning) was designed to the codes then in effect in North Carolina and the United States. The minimum sizes of furnaces, air conditioners and pipes as required by codes was totally inappropriate for the extreme insulation value of the earth berm, heavy roof insulation and insulated glass. In temperatures down to 18 degrees, if the wind was not blowing, the air conditioners would turn on!
The reason for the strange behavior of the HVAC systems was that the heat generated by fluorescent lights and human bodies was sufficient to heat the buildings above that temperature. With special permission of the Asheville Building Inspection Department, we changed the controls on the HVAC systems to have a third type of cycle. Fresh air from the outside is used to air condition the buildings between temperatures of 16 ᵒ F. and 65 ᵒ F. Earth sheltered buildings designed by this architect since then have also required the fresh air – air conditioning cycle for mid-range outside temperatures.
While designing earth shelter structures in temperate and semi-tropical regions, this architect found that applying a layer of earth over the roof was never cost-efficient. Not only does the earth required far more expensive structural systems, it creates the need for much more extensive water proofing of the roof and humidity control in the building.
Why an earth berm?
The earth berm has several functions. It insulates the interior of the house from extremes in outside air temperature. It insulates the house from outside noises and flying projectiles such as falling tree limbs and bullets. The slope of the berm deflects high winds over the structure, so lateral wind forces do not put excessive pressure on a vertical wall. Because of the Bernoulli Effect that also allows airplanes to fly, the passing over of the winds causes uplift.
Architects (if they are astute) must provide far stronger anchors for the walls and roof of an earth shelter house than is typical of a conventional house. Otherwise, negative wind pressure created by Bernoulli Effect the tornado as passes over a dome-shaped earth shelter house, could suck the roof, people and furniture right out of the house. While preparing a technical report on the unexpected total destruction of a group of super-beefed up houses in Slidell, Louisiana during Hurricane Katrina, I found that the Bernoulli Effect was a major culprit. Maelstroms (whirlpools) were the other culprits.
The physical mass of the earth functions as an ideal buttress which braces the wall laterally. Walls topple in a tornado because the difference in wind pressure between the top and bottom of the wall, plus lack of lateral support for most of the wall, create a rotation force on the wall. Architects and engineers use “fancier” words for this manifestation of physics, but the principal is the same.
Socio-economic and political attitudes
Earth shelter houses use a fraction of the energy of the average conventional house. They have starkly lower maintenance costs. They can potentially withstand the most powerful tornado, with perhaps only the loss of some windows. Nevertheless, they have never been accepted by the real estate community and in fact, very few have been built in the past two decades.
The explanation for their scarcity is not pragmatic factors. If one had the opportunity to pay less for a house, have much lower energy and maintenance costs, and be the only survivors of a tornado that leveled your neighborhood, it would seem to be a no-brainer. However, there were intangible factors that caused the concept to be almost abandoned in the 1980s.
Culturally, the concept of earth shelter housing was associated with the “Hippie Era” of the Johnson & Nixon Administrations and the “Back to Nature Movement” of the Jimmy Carter Administration. In 2002 some clients ordered passive solar features and a wooden stove removed from their mountainside house design because they said, “Our friends who visit here will think we are hippies and Democrats.”
Shortly after the beginning of the Reagan Administration and continuing till the financial collapse that started the Great Recession, housing was viewed by affluent North Americans as a statement that “we are successful!” Particularly, during the 1980s and 1990s, upscale residential architecture tended to be very ostentatious, while the remainder of society was jammed into tiny lots and cookie-cutter, vinyl sided shoe boxes.
An earth sheltered houses blend into their environs. Wearing a Reagan Era gold chain around your neck and a Rolex watch with diamond insets on your wrest is a far more effective means to express one’s insecurity than building a passive solar house with earth berms.
The real estate finance industry of the late 20th century and first decade of the 21st century preferred that all houses and humans look alike. They viewed both houses and humans as commodities. Mortgage bankers found it was easier to create financial packages of house loans, if the houses were standardized. Who wants a 15 pound brown chicken gumming up the works of a chicken processing plant that normally only butchers 6 pound white chickens? Earth-shelter houses in particular and architect-designed houses in general, were disliked for the same reasons.
Real estate brokers and developers have always been wary of earth-sheltered houses. Again, because they are not standard, the fear is that they would stay on the market for long periods before selling to eccentric purchasers.
There are several economic indicators that suggest that North America’s culture is evolving away from blatant ostentatious behavior. Mortgage lenders will no longer be inclined to provide loans for extravagant houses that could potentially sit on the market for months. Houses are likely to be more compact and cost efficient in the future, because the Middle Class now has less discretionary income available for housing. An era of frugality is when the earth shelter house may become socially acceptable among the mainstream of the real estate and construction industry.
Readers wishing to ask Mr. Thornton questions about architecture, urban planning or Native American history may write him at NativeQuestion@aol.com.