I have a slab under my house of about 20". I have one window that bows. I have recently noticed a small crack appearing in the slab under of this window. My house is 50 feet wide, how can I find out if there is a crack in the center of my slab? I have only owned the 17 year old house for one year. If there is a crack, is there a way to prove if the previous owners knew about it, and what will be the approximate cost to repair it? My house does have pilings driven underneath it.