There's no floor under the walls of your house, if you could see under them.
thats not quite true.
Maybe other walls were added in after your house was built?
Every wall on the first level of a house has a floor under it. Its called the foundation. In a pier and beam house, there is still a flat, house-wide surface upon which the walls are built. On the second story of houses, if a wall is on top of another wall, then there may or may not be a floor. If a 2nd story wall does not have a wall below it on the first story, it will generally have the "floor" of the second story extending underneath it for support so that wall doesn't start to droop in relation to the rest of the room.
A wall consists of a bottomplate piece (normally a 2x4) nailed into the foundation/floor or screwed down with massive all-threads on the exterior of the house, especially in tornado country. Upon this baseplate the studs are aligned and then a header is put into place on top of the wall. Usually there is about a 1.5ft space between levels where joists are placed for load-bearing necesities(ack sp? on that word?)/ ducts/plumbing/wiring/etc.
If you walk into any 2 story house under construction and look up into that space, you will see the "floor" of the next level, but not any of the walls from underneath. To locate the walls, look for where romex electrical lines and plumbing are travelling between floors.
If you live somewhere besides America, this may not apply. I have heard that all houses in South Africa are made
entirely from stone so that might work out different. Dunno.
GMcG
ps: wow, had no idea I was gonna write that much. I guess you can tell I do a lot of work in houses during construction.