Including a basement as part of new house construction can increase the cost of the house by $10-$25 or more a square foot for an unfinished basement, or about $10,000-$50,000 or more for an average house; and $30-$100 or more a square foot for a finished basement, or about $35,000-$175,000 or more for an average house; with costs depending on location, soil conditions, the size and shape of the basement area (unique shapes with more than four corners cost more), the materials/finishes used ...