Description
Direct systems regulate indoor temperature by using conduction through building elements. Generally speaking, the largest climatic advantage of this system is in helping cool the living space. Buildings can be earth-covered in varying degrees. If the structure is built on the surface grade and earth is added around it, it is considered a bermed structure. Buildings can be constructed below grade or into hillsides and be totally or partially covered by earth. It is extremely important to keep moisture (ground water, rain, or other) from entering these structures. Various methods can be employed, such as the use of a drain medium.
Performance Characteristics
From the standpoint of the quality of the energy source, earth-sheltering and solar energy are superior to fossil fuels. The strong points of earth-sheltered structures include noise reduction, reduced impervious cover, storm protection, and the capability to blend with the natural environment.
Insulation
Insulation of the roof will depend on the structure's design and must meet the City of Austin energy code. If the building is bermed, the upper portion of the building should be insulated to the same standards used in aboveground structures.
Earth-Covering
An earth-covered roof should be limited to no more than 3 feet of soil. 12 to 24 inches (adequate for plant growth) is the typical range of depths for an earth-covered roof. This is too shallow to effectively insulate the building and is the reason that additional roof insulation is required.
Indoor Air Quality
High humidity in our region will require that well-designed levels of ventilation and/or dehumidification be incorporated into these types of structures. The lack of air infiltration in an earth-sheltered structure intensifies the need to eliminate pollutants within the house. See the section on Energy Recovery Ventilators in this Sourcebook for an explanation of mechanically controlled air infiltration. These can mitigate such concerns and should be thoroughly considered, particularly those models with humidity regulation capabilities.
Lighting
As in passive solar structures, an earth-sheltered home should be set on an east/west axis. The glass area then lies predominantly on the south wall (see the Passive Solar Design section in this Sourcebook) . Light wells are often added to bring light into the interior of the house. Interior surfaces can be designed to reflect light deep into interior spaces. The light wells should be designed to admit indirect summer light by having a roof and open sides.
Waterproofing Options
Polyurethane-based liquid applied waterproofing systems:
Application requirements and characteristics make these difficult to use successfully.
Vulcanized and plastic sheets:
Recommended for this area: butyl, EPDM, neoprene, and CPE. Seams should be minimized with these materials.
Bentonite clay products:
Available in various forms. Spray on, trowel on, and cardboard panels are commonly used in underground buildings. Interior leak repairs can be done with bentonite. Backfilling must be done with care, and application skill ranges from low (trowel), to moderate (cardboard panels), to high (spray).
Overall Considerations
The construction techniques required for earth-sheltered homes are quite exacting and should be extensively studied before building. Site-specific techniques should be used that account for soil characteristics, topography, rainfall characteristics, ground water levels and pressure, loading, and slope stability. |