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 in 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, the structure itself must be carefully planned in order to carry the load of the earth.
Considerations must be made 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 a great deal of stress on the walls. To help with this, drainage pipes are installed to protect the structure from water infiltration.
Underground homes are typically made of reinforced concrete because it does not degrade and exhibits 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 will not adequately insulate the inside. Earth does provide a great deal of insulating ability. But the addition of artificial insulation will help to control temperatures within the structure and limit the use of heating devices.
Finally, homes below grade must be extensively waterproofed. The most common systems include rubberized asphalt, plastic sheeting, 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 this hillside and bury a portion of your home. In these types of earth-sheltered homes, one wall is typically left exposed so windows can be installed 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.
Before you build an earth sheltered or underground home, it is important to evaluate several factors. Consider the climate. The best climates in which to build these homes are those with extreme temperatures, particularly places that experience dramatic temperature swings from day to night. However, a humid climate can create additional condensation issues for an earth sheltered home.
Evaluate the location of the water table and frost line. If it is too close to the surface, then it might not be possible to build an underground home. Also, consider the typography and which type of earth sheltered home would be the best fit for 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 an earth sheltered home. Sandy and gravelly soils are the best, while soil containing a lot of clay is not suitable.
Pros and Cons
- Protection from the elements
- Energy conservation and consistent indoor temperature
- Privacy since earth-sheltered homes have few windows
- Soundproofing against neighbors and nearby roadways
- Extra green space and insulation provided by a living roof
- Low maintenance, little to no exterior materials
- Poor ventilation and low indoor air quality
- Limited access to natural light, though some can be incorporated
- High upfront cost for excavation, beefed-up structure, and waterproofing
- Potential for water leaks
- High interior humidity (though this can be controlled with dehumidifiers)
- Danger of radon infiltration
- Poor acoustics
- Difficulty in finding professionals experienced with this alternative building method
- Concrete and waterproofing systems aren't eco-friendly building materials
- Local building codes may be prohibitive
- Zoning issues may not allow you to build it
- Limited options for expansion later
- Difficult to sell on the real estate market