
For all houses, you’ll actually find that there is a lot of space that you can’t see into!
For instance, we need a place for the pipes for the plumbing to go through, and the electrical wires that run through for the lights/light switches and electrical outlets. These can’t exist in a vacuum. Also, buildings will have space under the floors, as well. No matter how sturdy a house is built, you’ll find that mice and other rodents will always find a place to live, and this is the kind of space that the small folk use for their homes.
If there ever was a solidly built house, you wouldn’t find small folk living there, but that is definitely an out-of-the-norm situation.
