Award-winning builder Robert Rhoads, for example, has turned the traditional American home upside down, expanding the lower level’s size and improving design details.

   “Our secret has been to keep the ceilings high—9 or 10 feet,” Rhoads says. “Then we add dramatic impact so that your eyes are directed toward entertainment centers and custom detailing.” Rhoads also makes certain that the stairway leading downstairs feels open, like a stairway in any other part of the house, not a passageway into a cavern.

   Any underground space used for living is said to be “conditioned” and will require special insulation and moisture protection. Several systems now offer dramatic improvements over the conventional concrete wall.