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Earth Sheltered Home Design
If you are looking for a home with many energy-efficient features that will provide a comfortable, tranquil, weather-resistant atmosphere, an earth-sheltered house could be right for you.
There are two basic types of earth-sheltered houses:
* Underground
* Bermed (or banked with earth)
Both types usually have earth-covered roofs. Some roofs may have a vegetation cover to reduce erosion.
Designing Underground Earth-Sheltered Homes
When an entire earth-sheltered house is built below grade or completely underground, it's called an underground structure. The atrium or courtyard design can accommodate an underground, earth-sheltered house.
Atrium or Courtyard Design
An earth-covered dwelling may have as little as 6–8 inches (0.2 meters) of sod or as much as 9 feet (2.7 meters) of earth covering the structure. An atrium design offers an open feeling because it has four walls that give exposure to daylight. This design uses a subgrade open area as the entry and focal point of the house.
The house is built completely below ground on a flat site, and the major living spaces surround a central outdoor courtyard. The windows and glass doors that are on the exposed walls facing the atrium provide light, solar heat, outside views, and access via a stairway from the ground level. Atrium/courtyard homes are usually covered with less than 3 feet (0.9 meters) of earth primarily because greater depths do not improve energy efficiency. This style also offers the potential for natural ventilation.
The atrium design is hardly visible from ground level and barely interrupts the landscape. It also provides good protection from winter winds and offers a private outdoor space. This design is ideal for an area without scenic exterior views, in dense developments, and on sites in noisy areas. Passive solar gain—heat obtained through windows—might be more limited, due to the window position in an atrium plan. Courtyard drainage and snow removal are important items to consider in design.
Designing Bermed Earth-Sheltered Homes
A bermed earth-sheltered house may be built above grade or partially below grade, with outside earth surrounding one or more walls. Such a structure can accommodate more conventional earth-sheltered house designs, such as elevational and penetrational.
Elevational Design
Elevational plans expose one whole face of the house and cover the other sides—and perhaps the roof—with earth. The covered sides protect and insulate the house. The exposed front of the house, usually facing south, allows the sun to light and heat the interior. The floor plan is arranged so common areas and bedrooms share light and heat from the southern exposure.
This type of house may be placed at varying depths below ground level and is usually set into the side of a hill. The view provided will be one of landscape, rather than open sky, as in the atrium design. A structure designed in this way can be the least expensive and simplest to build of all earth-sheltered structures.
The elevational design may have limited internal air circulation and reduced daylight in the northern portions of the house, though there are ways to alleviate these problems by using skylights. The wide design of the house can be offset by close attention to architectural details, landscaping, and exterior materials.
Penetrational Design
In a penetrational design, earth covers the entire house, except where it is retained for windows and doors. The house is usually built at ground level, and earth is built up (or bermed) around and on top of it. This design allows cross-ventilation opportunities and access to natural light from more than one side of the house.
Site-Specific Factors for Earth-Sheltered Home Design
Before deciding to design and build an earth-sheltered house, you need to consider the building site's climate, topography, soil, and groundwater level.
Climate and Topography
The climate in your geographical area will determine whether an earth-sheltered house can be a practical housing solution. Studies show that earth-sheltered houses are more cost-effective in climates that have significant temperature extremes and low humidity, such as the Rocky Mountains and northern Great Plains. Earth temperatures vary much less than air temperatures in these areas, which means the earth can absorb extra heat from the house in hot weather or insulate the house to maintain warmth in cold weather.
The site's topography and microclimate determine how easily the building can be surrounded with earth. A modest slope requires more excavation than a steep one, and a flat site is the most demanding, needing extensive excavation. A south-facing slope in a region with moderate to long winters is ideal for an earth-sheltered building. South-facing windows can let in sunlight for direct heating, while the rest of the house is set back into the slope.
In regions with mild winters and predominantly hot summers, a north-facing slope might be ideal. Every site differs, but generally southern exposures offer more sun and daylight throughout the year than north-facing slopes. Most designs can be built to take advantage of each site.
Soil
The type of soil at your site is another critical consideration. Some types of soil are more suitable than others for earth-sheltered construction. For example, the best soils are granular, such as sand and gravel. These soils compact well for bearing the weight of the construction materials and are very permeable, which means they allow water to drain quickly. The poorest soils are cohesive, like clay, which may expand when wet and has poor permeability. Soil tests, offered through professional testing services, can determine load-bearing capability of soils and possible settlements that may occur.
Radon is an invisible and odorless radioactive gas produced naturally when uranium in rock decomposes. It is found in the soil and in outdoor air in harmless amounts, but can reach dangerous levels when trapped. Radon levels are another factor to consider in locating your home. Areas with high concentrations of radon can be hazardous, although there are methods that can reduce radon buildup in both conventional and earth-sheltered dwellings.
Groundwater Level
The groundwater level at your building site is another important consideration. Building above the water table is almost essential. Choosing a site where the water will naturally drain away from the building is the best way to avoid water pressure against underground walls. The site should be surveyed for low spots and areas where water will collect. Seasonal or regular surface water flows should be channeled away from the structure. Drainage systems must be designed to draw water away from the structure to reduce the frequency and length of time the water remains in contact with the building's exterior. Underground footing drains similar to or greater than those required by a house with a basement are necessary in many cases.