cost to add a basement
1 Adding a basement to an existing house can cost $30,000-$70,000 or more, depending on the size of the existing crawlspace or half-basement or if the house is on a slab foundation, and how much of the work is do-it-yourself and how much is done by contractors. In warmer climates where the foundation does not have to be as deep (typically 18-20 for a crawlspace or a few inches for a slab foundation), including a basement adds more to the total cost of the house because it requires a lot more additional excavation, far beyond what would be done without a basement.