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Air-gap membranes have been used in Europe and Canada for years. Manufacturers claim that combined with a good footing drain the membrane provides dry, odor-free basement living space. I recently had the opportunity to install one of these products on a new foundation in northern Vermont. The membrane, called Delta- MS, is made by Cosella D¨orken, a German company with North American offices in Ontario (888/433-5824). The membrane is a 6-mm-thick (24-mil) high-density polyethylene (HDPE) with a matrix of round dimples, about 5/8 inch in diameter, vacuum-formed into the sheet (see Figure 1, next page). The dimples are installed against the foundation and cause the membrane to stand off the concrete by about 5/16 inch, leaving an air space between the membrane