We are in the process of building a home. The builder uses a poured foundation and we purchased the optional 12-course foundation. We were a bit suprised when we measured the distance from the finished basement floor to the bottom of the floor joist - 7'6". We were under the impression that a 12 course foundation would provide at least an 8' floor to joist height. What is considered the standard depth for a 12-course foundation?