If the only difference between two houses is one is a 1-story and the other is a 2-story, then why does the 1-story house cost more per square foot? The reason a 1-story house in Spring Texas costs more per square foot than a 2-story is because it costs more to build the 1-story house.
Two of the most costly parts of a house are its roof and its foundation. A 2-story home with the same square footage as a 1-story Spring Texas home will have half the roofing costs and half the foundation costs. There are other economics achieved in building up versus out but the foundation and roofing are the two main cost savers.