Slab on Grade Foundation With No Grade Beam or Footing
I am hoping someone can answer a question I have regarding an existing slab on grade foundation that I would like to build on.
It is a roughly 20′ x 18′, 6″thick slab that was poured next to an old detached garage that I am currently remodeling. I don’t know when it was poured because I just purchased the home a little over a year ago, but it is level and square, and appears to be in good condition. It currently supports a lean to that spans the length and width of the slab. I would like to tear this down and build a fully enclosed, single-story addition in its place.
The issue is that there is no grade beam or footing for the slab. It is just a solid 6″ thickness all the way around. My question: Is there a way to dig around the perimeter and pour a grade beam or footings underneath the slab without destabilizing it? If that is not an option, would I able to dig adjacent to the perimeter and pour a stem wall around the slab? And if neither of those are possible, is there another solution that anyone might have to offer?