Many people think that having a concrete slab in the crawl space is a great idea and will keep water from getting in. This is not true and making this mistake can cost you far more than a dirt floor slab. This crawl space cost 3 times the normal amount to install drainage to fix the problem. Image the labor it takes to dig a trench all the way around the perimeter of your foundation. Now think about how much more labor is needed to jackhammer all the concrete up and haul it out in a 2-3 foot space. Now you can start to see why this is a very bad idea!