Here in the US, "inhabitable" includes not only the area, but also the height of the loft--most tiny home lofts don't get much over 4 feet high, so aren't considered "inhabitable". I've also seen a neat tiny home design which DOES create stairs and a 6'-height upper walkway on one side of the home, pushing the bedroom loft to the other side. The space under the walkway is used for things like the refrigerator, kitchen sink area, or closets/storage.