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<br /> . Charles A. Lane
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<br /> FIG. 7. Bentonite panels will provide waterproofing for the roof and walls of this house. The wall panels will be
<br /> applied at the base of the side walls up to approximately 8 feet. After backfilling the lower 8 feet, the second
<br /> level of panels will be applied and side backfilling completed. On the roof, 6 in. of styrofoam are placed directly
<br /> above the bentonite, and a 4 mil polyethylene sheet completes the waterproofing system. The plastic sheet keeps
<br /> • the styrofoam clean of fine dirt and sand and provides some protection during roof backfilling.
<br /> What properties should be considered in choosing
<br /> This is an important requirement since water-
<br /> insulating materials for earth-sheltered homes? absorbing insulations rapidly lost their R-value (the
<br /> The other product (i.e., besides waterproofing) ability of a material to resist heat flow). The most
<br /> usually applied to the exterior of the structure is commonly used insulating product that fulfills the
<br /> insulation. This is necessary when the structural above criteria is extruded polystyrene. It is a closed
<br /> system is that of high thermal mass such as concrete. cell, rigid board insulation with good long-term
<br /> A large amount of concrete used in the structure thermal performance. It should also be distinguished
<br /> represents a potentially large thermal storage mass, from expanded polystyrene, which is basically an
<br /> which must be insulated to work effectively. open cell product. Open cell insulation will absorb
<br /> Placing insulation on the outside exposes it to moisture from the ground over an extended period of
<br /> moisture and soil conditions. Usually the insulation is time. Two different production processes are used in
<br /> producing extruded and expanded polystyrene.
<br /> placed outside of the waterproofing system because Another concern regarding insulation placed on
<br /> most waterproofing systems need a smooth, dry,
<br /> stable base, such as the concrete structure for the exterior is the possibility of rodent and insect
<br /> application. Except for butyl sheets, waterproofing damage;both time and possible research into this area
<br /> products should not be applied over the insulation. should reveal whether or not this concern is
<br /> There is too much potential movement of insulation, warranted.
<br /> whether it be rigid board or poiyurethane liquids, to Insulation placement should be maximized under
<br /> form a stable base for the waterproofing. Placing the root soil and upper portions of the walls. These areas
<br /> insulation over the waterproofing also will protect the are most susceptible to temperature fluctuations of
<br /> waterproofing during backfilling. the outside air. Nonbermed house portions,such as a
<br /> south wall, should be conventionally framed and
<br /> insulated.
<br /> How do the construction costs of an earth
<br /> sheltered home compare with costs for a comparable
<br /> conventional house?
<br /> What are the necessary properties for exterior
<br /> • applied insulation?
<br /> First, they must have good compressive strength to
<br /> resist earth pressures. Second, they should be a closed
<br /> cell product that will not absorb excessive moisture. Regardless of promises of energy savings and
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