Add-on slab foundations
It is not unusual for an older home in Houston and surrounding areas to have what are called add-on foundations. Add-on foundations are just extensions to the original slab foundation. Consider the following example. The house has an L-shaped slab as shown. Notice that the master bedroom and bath are at the rear right. There are many homes like all over town. If they are older, say 20 years or more, the master bedroom is about the same size as many new homes, but the master bath is far smaller.
If you extend the foundation in the master bath outward toward the back yard, you can easily build a new, much larger master bath. Rather another, newer home you can simply add onto your existing home. For many people, this is an attractive option.