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148 Charles A. Lane — as: "earth pipes." trombe walls, heat storage, natural can prove to be the most demanding. Products will ventilation, solar gain systems, wind, and the use of range from good resealing properties to none at all. renewable resources such as wood burning and Be sure to consult the manufacturers' test data on alcohol fuels. Properly designed earth-sheltered this. Performance test results of a product should be homes should have heating loads well within the available from the product manufacturer or from • capabilities of an efficient wood stove even in very independent testing sources;any product that appears cold climates with an excess of 8000 degree days per weak in one or more of the abovementioned areas year. should be eliminated. No matter what type of Generally, mechanical air-cooling systems have not structural material is used, there will always be some been necessary in properly designed earth-sheltered settling and possible structural cracks, so the houses. Because the temperature of the surrounding waterproofing must have the ability to bridge the earth is almost always cooler than the inside of the cracks and protect the house from unwanted house, excess specific heat will Clow from the house moisture. During construction. it is easy to scrape off, into the soil. Initial fears regarding condensation and tear or rip the waterproofing product once applied. high indoor relative humidities have not materialized. Nails, sharp rocks, work boats and careless backfilling Good air circulation usually will control most can take their toll. high-humidity situations, and in extreme cases a small When used in conventional above-grade structures, portable dehumidifier should suffice to control some waterproofing products will reseal quite well. humidity. This is primarily due to the warm extremes in air As knowledge of the energy performance becomes temperature: heat will cause the material to soften accessible, mechanical engineers should be able to and then allow it to reseal. Asphalt products are effectively standardize and size systems to perform especially adaptable in this way. the necessary HVAC functions for an earth-sheltered Below grade, however, temperatures are lower, house. Ideally, the systems will incorporate the good ranging from 35 to 70°F, far below the high design of current HVAC systems and the best of new, temperatures of 150-180°F that can be reached on energy-efficient solar energy and passive-energy tech- an above-grade, built-up roof system. Most products niques. Such a system would be a great boon to the specify that during application air temperatures be earth-sheltered housing industry. above 40°F; otherwise the bonding or curing processes will be retarded. - What waterproofing systems are most appropriate for earth sheltered homes? On the other hand, repeated thermal expansion of The most frequently asked questions about a material is one of the greatest forces leading to earth-sheltered housing concern waterproofing. The wear. It may be argued that the narrow thermal spectrum of underground temperatures will aid in the possibilities of leaks in an earth sheltered house inspire fear in the minds of professionals and lay durability of product material, yet to answer this people alike. quantitatively, much research on underground water- Unfortunately, sound knowledge and experience proofing systems is needed. in applying waterproofing systems to earth-sheltered Finally, whichever waterproofing system the homes are scarce. Experts offer ample opinions but builder chooses, quality control is essential. Even the very few facts. Extensive, independent testing of best material can prove a disaster if improperly current waterproofing systems and the development installed. It is questionable whether the novice, of new products is imperative. do-it-yourself, earth-sheltered home builder should At present, five major products are being used for attempt to install waterproofing himself or herself. waterproofing earth-sheltered homes: asphalt and The job is better left to a waterproofing contractor pitch products;bituthene;liquid polyurethanes;butyl who knows the product. Only with repeated and EPDM (Ethylene Prophylene Diene Monomer) application experience can one know how to cope membranes; and bentonite products. Each product best with unexpected problems and their conse- has advantages and disadvantages; none can be quences. It is best not to make your house your described as universally "the best." These products guinea pig. should be distinguished from dampproofing products, In waterproofing, extra care must be taken at the which only restrict vapor transmission. In addition, seams (if any) and points where the flashing projects good surface drainage practices and proper backfill from the building. Water has a way of finding the are essential for an adequate waterproofing system. weak link in a waterproofing system. Skylights can Regardless of which waterproofing system is used, cause problems if the mechanical details are not well the product should: (1) have a long service life designed, though some apparent leakage attributed to - underground; (2) have good crack-bridging capa- skylights has actually been due to interior condensa- bilities; and (3), ideally be able to reseal itself at tion problems rather than to a failure in the exterior underground temperatures. The third requirement waterproofing system.