This week, the CalFinder spotlight goes to earth homes. Homeowners everywhere want to know what makes these homes tick. I managed to steal a few moments from Paul Shippee, an internationally-known solar architectural designer and civil engineer, to find out more. Paul has designed and built numerous passive solar homes, including energy-efficient retrofits and zero-energy solar homes. He founded Crestone Solar School in the small mountain community of Colorado, where he teaches sustainable philosophies and the fundamentals of solar technology.
Paul says earth homes are growing in popularity. Below, he tells us about the many varieties and why they conserve more energy than the conventional home. According to Paul, most homes around the world are made from earthen materials, though some U.S. homeowners are apprehensive about their “cave-like” ambiance and unique curb appeal. However, you’ll find these homes have aesthetic charm as well as superb insulation, temperature control, and sound proofing capacity. For these reasons, earth homes tend to cost more than others. Read my interview with Paul to find out more.
Which U.S. regions contain the highest number of earth homes? Are they growing in popularity?
Most earth homes seem to be in the American Southwest – Arizona and New Mexico, with some also in Texas and the Midwest. These earth homes are used for both heating and cooling and typically feature high volumes and areas of earth for thermal mass exposed on the interior. This is for moderating temperature swings both day and night. They seem to be growing in popularity based upon the requests I receive for information.
Is there more than one type of earth home? Can you explain their general characteristics, and what makes them different from one another?
Most homes all over the world are made from earthen materials. Rammed earth, adobe, and cob walls seem to be both the oldest and the most numerous types. In the more temperate climates these are typically characterized by thick walls (12-36 inches) of mud/dirt materials and function passively with moderate interior temperature swings for both heating and cooling with no added insulation. In colder climates, added insulation on the exterior or mid-wall is usually necessary.
Another type of home might be called earth-covered or earth-sheltered with dirt on the roof, sometimes called a living roof that will support vegetation. This type of earth home requires extra structural supports for adequate safety due to the heavy earth loads overhead. A variation of this is an earth-bermed house, where earth is banked up to various heights on the east, west and north sides, leaving the south side open for solar gain windows. A newer type of earth home popular in Arizona is known as cast earth, where a mixture of earth and lime is poured into forms much like concrete. One other use of earth in home construction is in straw bale homes where earthen plaster is used to coat the inside and outside of the straw bale walls. Another use of earth building is to make floors out of earth materials, sometimes known as polished adobe floors.
What makes the earth home green? What are the biggest ways they help conserve energy?
The biggest way an earth home saves energy might be the conservation of what is known as “embedded energy” which is the energy in the manufacture and transportation to the site of conventional materials such as concrete and wood. Over the lifetime of the building energy consumed for heating might be similar to an energy-efficient conventional home, but considerable energy savings are often realized in climates where cooling costs are high for air-conditioning. These different kinds of energy should be quantified and compared in order to assess the green qualifications of new construction. Beyond these considerations, the best way to make any home green is to, first, provide super insulation in walls and ceilings, caulk cracks well, and then orient the long side to the south with many windows to let the sun in, and finally to provide thermal shades to keep the warmth in on long, cold winter nights.
In your opinion, what makes the earth home aesthetically pleasing? What are your favorite features?
One of my favorite features of an earth home is the pleasing look of all the various earth tones that can be achieved, inside and out. This feature is especially popular in the Southwest. Another thing I like is the thick walls which add a pleasant deep aspect to where the windows are located, especially if the walls enclosing the windows are angled out toward the interior. The sound proofing quality of earthen construction is appealing too. Of course, a “living roof” can add a charming feature as well.
What are the disadvantages, if any, to owning an earth home?
I have heard people express apprehension when they anticipate a cave-like feeling that might be associated with earth-sheltered homes. However, this can be overcome by placing skylights to naturally light the north walls. Another disadvantage I have encountered is what is known as “curb appeal” in the real estate market. A situation where only the south side is open to gain sunlight, and the north side is covered with earth, scares some people interested in resale value.
What is an earth home kitchen typically like, and what are some typical upgrades one can make to it?
There is no reason that an earth home kitchen would be any different than in a conventional home, that I know of.
How can homeowners with more conventional homes use the earth home model to apply environmentally friendly characteristics to their own homes?
They probably cannot do it because the walls and roof of conventional homes are not suitable for supporting heavy earth which may also absorb water or moisture and stress wall materials beyond what they are intended for. It would not be cost-effective to modify a conventional home to accommodate earth materials.
Are there any particular resources you recommend to homeowners looking to learn more about earth home?
Just Google terms like earth homes, earth-shelter, earth-covered, adobe, cast earth, earthen plaster, rammed earth, cob, adobe floors, etc. and a wealth of references, books, and articles will appear before your eyes. Also, any resourceful and innovative builder should be able to assist an adventurous and capable designer to produce an earth home almost anywhere. A south-facing hillside is ideal but not necessary because earth can be banked up if it is available at low cost.
Do you have anything else to add?
Yes. Earth homes have a tendency to cost a little more, depending on how they are designed. Also, an earth-covered building is vulnerable to moisture and water seeping into the earth, and this eventuality will require extreme caution in the design and construction details to prevent future remediation and repair costs. Another consideration is whether toxic radon gas is present in the earth materials that are exposed to the house interiors.
Thanks, Paul, for a great interview!
Have you got a home type you’d like to see in the Right Style, Right Remodel series? Send us a comment! Happy remodeling.