At some point in your life, you've probably played with dirt. It's a practice that many people around the world and throughout history have continued long past childhood, using the abundant material to construct shelters.
Earth-sheltered homes, including underground homes, are becoming a viable passive design strategy. At one time, earth-sheltered homes were either found in traditional cultures or high-end building designs. Now, earth-sheltered homes are entering the mainstream for their natural insulating ability.
What Is an Earth-Sheltered Home?
When you build into the ground, the earth functions as a thermal mass, helping to maintain a comfortable interior temperature year-round. However, you must carefully plan the structure itself to carry the load of the earth.
Your considerations are outside the realm of traditional home building. For example, retaining walls must be constructed to hold back the weight of the earth. Especially as it becomes water-logged, the earth's hydrostatic pressure can exert great stress on the walls. Drainage pipes help protect the structure from water infiltration.
Underground homes are typically made of reinforced concrete because it does not degrade and has high compressive strength. Dome structures are popular because of how well they distribute the weight of the earth.
A layer of insulation must also be installed, as the earth alone does not adequately insulate the inside. Earth does provide a great deal of insulating ability. But the addition of synthetic insulation will help control temperatures within the structure and limit the use of heating devices.
Lastly, homes below grade must be extensively waterproofed. The most common systems include rubberized asphalt, plastic sheeting, and liquid polyurethanes.
Main Types of Earth-Sheltered Homes
In-Hill Sheltered Homes
If the topography of your site includes a steep enough slope, it is possible to excavate into the hillside and bury a portion of your home. In these earth-sheltered homes, one wall is typically left exposed so you can install windows, and the structure can gain heat via passive solar methods.
Bermed Earth Sheltered Homes
On flatter sites, you can pack the earth against the exterior walls of your home so that it slopes away for drainage. The roof may or may not be covered by earth. Earth-covered roofs must bear considerable weight. But the advantage is that the earth adds yet another insulating plane to the home.
Underground Earth Sheltered Homes
To create a truly underground living experience, dig a large recess, construct your home below grade, and fill in the dirt around it. With this type of earth-sheltered home, a central courtyard is usually located to allow access to air and light. Otherwise, skylights or sun tubes may be installed to provide additional natural light.
It is important to evaluate several factors before you build an earth-sheltered or underground home. Consider the climate. The best climates to build these homes are those with extreme temperatures, particularly places that experience dramatic temperature swings from day to night. However, a humid environment can create additional condensation issues for an earth-sheltered home.
An architect or designer must ensure that the home is up to code. The building process begins with a civil engineer, who evaluates soil conditions and water runoff. Dave South, the publisher of the Dome News for the Monolithic Dome Institute, recommends that a structural engineer design a building strong enough to support the load placed over the home.
Evaluate the location of the water table and frost line. If it is too close to the surface, it might not be possible to build an underground home. Also, consider the typography and which type of earth-sheltered home would best fit the site. The number one rule is to always send water in the opposite direction from your home.
Finally, you must determine whether the soil is stable enough to support the construction of earth-sheltered homes. Sandy and gravelly soils are best, while soil containing a lot of clay is not suitable.
How to Find a Builder
Mariany Barboza of Green Magic Homes, a company that provides biophilic underground construction systems worldwide, recommends choosing an open-minded contractor. "Someone who says, 'Let's try before It can't be possible,'" says Barboza. Green Magic Homes can also connect you to a certified builder in your area.
Pros and Cons of Living in an Underground Home
Making a home underground or dug into a mound is an interesting prospect, but it is a major investment. Review some of the prevailing factors concerning construction, maintenance, and living in a confined space.
Protection from the elements
Energy conservation and consistent indoor temperature
More privacy with few windows
Soundproofing against neighbors and nearby roadways
Green space and insulation with a living roof
Low maintenance, little to no exterior materials
Grounded to earth and nature
Poor ventilation and low indoor air quality
Limited access to natural light
Higher upfront costs for construction
Potential for water leaks and higher humidity
Danger of radon infiltration
Difficult to find specialized builders for this construction
Challenging to repair
Concrete and waterproofing aren't eco-friendly materials
Building codes and zoning issues might be prohibitive
Limited options for future expansion
Difficult to sell on the real estate market
Evacuation issues in case of fire