• Energy & Power

Other Considerations: Earth-Sheltered Houses



Waterproofing

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

There are several waterproofing systems currently in use, including rubberized asphalt, plastic and vulcanized sheets, liquid polyurethanes, and bentonite. Each has its advantages and the one you choose will depend on your site and house plan.

  • Rubberized asphalt combines 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 sheets are 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 diene monomer, polychloroprene (neoprene), and poly-isobutylene. For all these materials, the seams must be sealed properly, or the membranes will leak.
  • Liquid polyurethanes are often used in places where it is awkward to apply a membrane. Polyurethanes are sometimes used as a coating over insulation on underground structures; however, weather conditions must be dry and relatively warm during their application.
  • Bentonite is a natural clay formed into panels or applied as a liquid spray. The panels are simply nailed to walls; the spray is mixed with a binding agent and applied to underground walls. When the bentonite comes in contact with moisture, it expands and seals out the moisture.

Humidity

may increase in earth-sheltered houses during the summer, which can cause condensation on the interior walls. Installing insulation on the outside of the walls will prevent the walls from cooling down to earth ; however, it also reduces the summer cooling effect of the walls, which may be viewed as an advantage in hot temperatures. Mechanical air conditioning or a dehumidifier is often necessary to solve the humidity issue. Proper ventilation of closets and other closed spaces should keep the humidity from becoming a problem in those areas.

Insulation

Although insulation in an underground building does not need to be as thick as that in a conventional house, it is necessary to make an earthen house comfortable. Insulation is usually placed on the exterior of the house after applying the waterproofing material, so the heat generated, collected, and absorbed within the earth-sheltered envelope is retained inside the building’s interior. If insulating outside the wall, a protective layer of board should be added to keep the insulation from contacting the earth. Depending on the type of structure—wood, masonry, concrete, or steel—insulation may instead be placed inside the walls before the waterproofing material is applied.

Air Exchange/Air Quality

Adequate air exchange must be carefully planned when building an earth-sheltered dwelling. Generally, well-planned, or ventilation by exhaust fans can dissipate ordinary odors. Any combustion appliances that are installed should be “sealed combustion units,” which have their own, direct source of outside air for combustion, and the combustion gases are directly vented to the outside. In addition, indoor pollutants emitted by formaldehyde foam insulation, plywood, and some fabrics can accumulate and become an irritant if ventilation is not properly planned.

A Home for the Future

If you are looking for a home with many energy efficient features that will provide a comfortable, tranquil, weather-resistant atmosphere, an earth-sheltered home could be right for you. With the general information in this publication and more details available from the sources listed below, you are on your way to owning a home that can protect you from the elements and the rising costs of energy and building resources.

– National Renewable Energy Laboratory, United States Department of Energy, Feburary 1997