Earth-Sheltered Homes

Ronald Frederick Greek

An earth sheltered home (thermal battery/mass & moderation of temperature extremes) can protect your family from the elements, without external utility connections.

One approach to the concept is well presented in the “Earthship” series of books by Michael Reynolds, ranging from single room ìpods” to luxury homes.   It’s not that earth is a good insulator, rather the advantage comes from that fact that earth is NOT a good insulator, and it takes a lot of heat, or cold, to make a large mass of earth change temperature.

While Mr. Reynolds emphasizes use of tires, cans, etc. in his structures, the functional aspects are relevant regardless of the construction material.   See John Hait’s book “Passive Annual Heat Storage” for scientific details of the thermal buffering system.

Stacked concrete block is advocated by architect Bruce Beerup in his website

Mike Oehler, in “The $50 & Up Underground House Book” presents his PSP system (post/shoring/Polyethylene), basically an underground pole building.   Regarding wood in contact with the soil, in most soils, the area of decay is just below ground level, where soil microbiological activity is greatest. Often a post can be almost completely rotted out at this level, while the wood several feet deeper in the ground is still solid. So it’s possible that a post, buried two feet or more into the ground, in an excavation already as much as six feet or more in the ground, will last a very long time.  In addition, Oehler points out the old-time observation that charred wood doesn’t rot. Chars the bottom two feet or so, by roasting them over a campfire, propane torch, etc.  For additional insurance, wrap the post bottom in several plastic garbage bags secured with duct tape.

Conventional thinking involves digging a hole into a hillside and plopping a structure there with a bank of windows facing downhill.  This makes the uphill side a solid blank wall, with the roof probably pitched back into the hill, so drainage from the roof runs into drainage from the hillside. Leaks are almost inevitable.

Mike suggests an uphill patio, basically a terraced garden area, with its bottom at any desired height from the floor of the house, and its top blending into the adjacent ground level. It not only solves problems of drainage and lateral thrust (the pressure of the earth on buried walls), but it can function as an emergency exit or a second entrance. It can also serve as a built-in greenhouse.  Naturally, it admits light and air, even from the uphill side of the house which would otherwise be a dark blank wall.

Assets, time, and limited labor may not permit large structures, but small does not have to mean primitive and uncomfortable.  Consider motor homes and boats, where individuals and families live comfortably in facilities the size of the living room in a typical American home.  I suggest you tour travel trailers, motor homes, power or sail boats, etc., for ideas.

The temperature of the earth at a depth of approximately 20 feet is essentially stable at the annual average surface temperature.  A home at that depth would probably not need any mechanical HVAC…nor would it have much of a view.  The technical aspects of correct earth sheltering are explained well by John Hait in his book “Passive Annual Heat Storage”.   The techniques will improve the feel of even a traditional home, but works best in homes specifically built to take maximum advantage of the buffering.

The greatest source of energy on earth is the sun, which appears to travel a fixed pattern in the sky that is readily estimated.  To maximize the benefits of shade, or of solar collection, the suns pattern of movement must be taken into account.

a. To artificially “lower” your home, insulate the ground for 20 feet out around your home with three layers, separated by heavy plastic sheets for waterproofing, of “Dow Blue Styrofoam”, white styrofoam board, or other appropriate insulation, then carefully cover the insulation with dirt, sand, gravel, etc to protect it from weathering.  Low-tech/natural insulation layers, such as grass, leaves, etc., with some waterproofing means or even layered with a high clay soil will help, but eventually need to be replaced.  Berming earth up the sides of the home provides additional protection from the large temperature changes of open air.  Even the roof can if you chose have a layer of earth on top of the insulation.  The soil need only be thick enough for the plants grown there.

b. A low energy method to tap the stable ground temperature is a pipe leading straight down into the ground (as in a driven well) 20 to 30 feet.  Any appropriate method of routing water down and back up in a sealed system (i.e. a small pipe inside a larger pipe) can allow a transfer of temperature to/from the depth.   Each pipe can be expected to heat/cool the ground in a  3 to 4 foot diameter circle, therefore space the “wells” 3 feet apart.  When the surface is significantly cooler than the bottom, a natural thermosyphon should occur.   With appropriate manifolds and valves, warmed or chilled water can be pumped from/to collectors/radiators or circulated in a hydronic system of pipe embedded in a concrete floor/wall.

c. Equator‑facing windows, vertical or angled to be 90degrees to the noon sun in the winter can provide significant passive solar heating in the winter while minimizing glass exposed to summer sun.  (In the summer, the sun rises and sets NORTH of the East/West glass alignment, and the glass can be shaded on the outside.)  Further summer solar gain can be avoided by almost any approach that provides a well ventilated shade area about a foot from the main structure.

d. Skylights.  Conventional skylights admit too much heat in the summer, and require a large opening in the structure of your home.  More diffused and useful light is admitted, with less heat, by “lighttubes”, essentially mirrored pipe with a lens cover on each end.  Venting can be separately done with insulated pipe with removable caps.    The combined opening in the structure is much smaller, the risk of weather damage is less, and maintenance is less.

The are options which have potential for development not only as lighting, but heating, cooling, and power.

e. Fireplace.  An interior fireplace must have an external air source.  Since the fireplace is probably only used when it is cool outside, arrange the air source such that it draws from the pantry, which would then be vented to the outside, cooling the pantry.

f. Roof / external mounted tube collectors, flat or with reflector concentrators, can heat water during the day, or cool water during the night.  Cooling can be enhanced by misting or water evaporation.  Used for cooling, the circulating water might “thermosiphon”.

g. Basic structure.  In the end, ANY system that provides you a waterproofed, insulated living space that is heavily insulated, has extensive thermal mass, and a practical means to get heat into and out of the mass can provide a comfortable home.