Efficient Earth-Sheltered Homes (2024)

If you are looking for a home with energy-efficient features that will provide a comfortable, tranquil, weather-resistant dwelling, an earth-sheltered house could be right for you.

There are two basic types of earth-sheltered house designs—underground and bermed.

When an entire earth-sheltered house is built below grade or completely underground, it's called an underground structure. An atrium or courtyard design can accommodate an underground house and still provide an open feeling. Such a 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.

The atrium design is hardly visible from ground level, creates a private outdoor space, and provides good protection from winter winds. This design is ideal for building sites without scenic exterior views, in dense developments, and on sites in noisy areas. Passive solar gain—heat obtained through windows—is likely to be limited because of the position of the home’s windows, and courtyard drainage and snow removal should be carefully thought through during design.

A bermed house may be built above grade or partially below grade, with earth covering one or more walls. An “elevational” bermed design exposes one elevation or face of the house and covers the other sides—and sometimes the roof—with earth to 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 can be the least expensive and simplest way to build an earth-sheltered structure. Strategically placed skylights can ensure adequate ventilation and daylight in the northern portions of the house.

In a penetrational bermed design, earth covers the entire house, except where there are 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 and access to natural light from more than one side of the house.

Like any home design, earth-sheltered houses have advantages and disadvantages.

On the plus side, an earth-sheltered home is less susceptible to the impact of extreme outdoor air temperatures than a conventional house. Earth-sheltered houses also require less outside maintenance, and the earth surrounding the house provides soundproofing. In addition, plans for most earth-sheltered houses "blend" the building into the landscape more harmoniously than a conventional home. Finally, earth-sheltered houses can cost less to insure because they offer extra protection against high winds, hailstorms, and natural disasters such as tornados and hurricanes.

The principal downsides to earth-sheltered houses are the initial cost of construction, which can be up to 20% more than a conventional house, and the increased level of care required to avoid moisture problems, both during construction and over the life of the house. It can also take more diligence to resell an earth-sheltered home, and buyers may have more hurdles to clear in the mortgage application process.

The type of soil at your site is another critical consideration. Granular soils such as sand and gravel are best for earth sheltering. These soils compact well for bearing the weight of the construction materials and are very permeable, allowing water to drain quickly. The poorest soils are cohesive, like clay, which may expand when wet and has poor permeability.

Professional soil tests can determine the load-bearing capability of soils at your site. Soil radon levels are another factor to consider, because high concentrations of radon can be hazardous. There are, however, methods for reducing radon buildup in both conventional and earth-sheltered dwellings.

The construction materials for each earth-sheltered structure will vary depending on characteristics of the site and the type of design. Materials must, however, provide a good surface for waterproofing and insulation to withstand the pressure and moisture of the surrounding ground.

Concrete is the most common choice for constructing earth-sheltered buildings, because it strong, durable, and fire resistant. Concrete masonry units (also called concrete blocks) reinforced with steel bars placed in the core of the masonry can also be used, and generally cost less than cast-in-place concrete.

Wood can be used in earth-sheltered construction for both interior and light structural work. Steel can used for beams, bar joists, columns, and concrete reinforcement, but must be protected against corrosion if it is exposed to the elements or to groundwater. It is also expensive, so it must be used efficiently to be economical as a structural material.

Waterproofing can be a challenge in earth-sheltered construction. Keep in mind these three ways to reduce the risk of water damage in your house: choose the site carefully, plan the drainage both at and below the surface of the house, and waterproof your house.

Waterproofing systems to consider include:

• Rubberized asphaltcombines a small amount of synthetic rubber with asphalt and is coated with a polyethylene layer to form sheets. It can be applied directly to walls and roofs and has a long life expectancy.
• Plastic and vulcanized sheetsare among the most common types of underground waterproofing. Plastic sheets include high-density polyethylene, chlorinated polyethylene, polyvinyl chloride, and chlorosulfonated polyethylene. Suitable vulcanized membranes or synthetic rubbers include isobutylene isoprene, ethylene propylene diene monomer, polychloroprene (neoprene), and polyisobutylene. For all these materials, the seams must be sealed properly to guard against leaks.
• Liquid polyurethanesare often used in places where it is awkward to apply a membrane, and are sometimes used as a coating over insulation on underground structures. Note that weather conditions must be dry and relatively warm during their application.
• Bentoniteis a natural clay formed into panels that are nailed to walls or applied as a liquid spray. When the bentonite comes in contact with moisture, it expands and seals out moisture.

Learn how switching to a cool roof can save you money and benefit the environment.

U.S. Department of Energy