There are two basic types of earth-sheltered housing—underground and “bermed” (or banked with earth). Certain characteristics such as the location and soils of your site, the regional climate, and design preferences are central to which type will work best for you.
Underground housing means an entire structure built below grade or completely underground. A bermed structure may be above grade or partially below grade, with outside earth surrounding one or more walls. Both types usually have earth-covered roofs, and some of the roofs may have a vegetation cover to reduce erosion.
From these two basic types, three general designs have been developed. They are the:
An earth-covered dwelling may have as little as 6 to 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. It 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 there is no benefit in energy efficiency from greater depths. 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.
The elevational and penetrational plans are more conventional earth-sheltered housing designs. 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.
However, the elevational design may have limited internal air circulation and reduced daylight in the northern portions of the house, although 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.
In the penetrational plan, 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.