The previous homeowner had a deck. Then he enclosed it. Then he dug out underneath it about 3-4 feet, cut into the foundation, and put a door from under the basement to under the deck. It's about 7ft high under there. I'm not sure if it's legal, or if he paid fines for it when he had to get it permitted to sell the house. It also has an entrance to outside, and has lattice work on the sides. We use it to store bikes, pool chemicals, shovels, and in the winter, firewood. We don't have any water issues with it, as he built up a stone and concrete wall around the area he dug up.
He also installed a patio that's not doing too well. I want to break it up and replace it with a deck. As an added bonus, I want to use underneath it as an extension of that storage space... But I'm not sure how much foundation is allowed to be exposed, or if this is safe at all. I will, of course, pour a concrete floor and walls for the underground portion of this.
This is Massachusetts, by the way... pretty sure I'm not on bedrock, and I know there's gravel and pipes underneath the basement floor if that information is pertinent. Part of the exposed foundation may end up being garage foundation, which may not even be as deep as the house foundation.. I'm not sure, though.