Abstract: The present modular foundation construction includes a plurality of interconnectable extruded modular forms configured to be selectively arranged and interconnected in the shape of a customized building foundation. The plurality of forms, when the shape of the customized foundation, define a series of interconnected first cavities extending around the shape for receiving poured concrete and further include a series of second cavities extending along the first cavities filled with insulation to form a substantially continuous insulative layer around the shape. Male and female connectors on the end wall sections of the forms provide a secure interconnection.