I have a small ?30' x 12'? addition. on a cement slab. I think the slab is 4 inches and was reinforced with some steel. Could this cement foundation be the roof for a root cellar?
Other than the edges of this foundation, it does not have to hold up anything but foot traffic. The building on top is a very minimal, one story board and baton single room, build up against an existing structure on one of its long sides.
Best Answer
30' x 12' is significant. Do not use this slab as a ceiling for anything accessible by humans and do not excavate under it, without having a professional contractor or engineer assess it first. If it was not engineered for that purpose it is not fit for that purpose and it is not worth the risk to assume fitness.
It should not be a big deal to support it from below with posts and beams.