On Fri, 22 Mar 2013 14:36:01 -0700 (PDT), Jim Walsh
wrote:

Hello all.
My 1950s brick-built house has a light weight block wall, on the first floor, separating the master bedroom from the bathroom. There is no corresponding wall, on the ground floor, underneath.
A while back, when doing some work in the room below the bedroom and bathroom, I made a hole in the ceiling to see how the wall above was supported. I expected to find an RSJ or beam, but there was nothing. I guessed that someone must have built the block wall directly onto the floor boards; far from ideal, I would imagine, but it's been in place for quite a few years without incident (though it is not original to the house).
Recently, I had reason to remove the skirting board that runs along the wall in question, in the bedroom. With the skirting removed, I can now see the base of the wall and it appears that the blocks are not sitting on the floor boards but are, in fact, fractionally aboove the floor boards. Does anyone have any idea what's going on here? To all intents and purposes, it appears that the wall is floating. The span is about 3m, so I would be surprised if it could all hold in place just from being tied in to brick walls at either end. One notion that occurs to me is whether there could be a supporting steel for the lowermost course and that the blocks are shaped in some way that conceals it. Is this plausible? Are such techniques well-known?
Suggestions appreciated. I'm reluctant to do too much exploratory excavation for fear of disrupting what might be a fragile structure!
Thanks, Jim.

All the upper walls in my 1979 house are like this, none are over a
lower wall.

They are a very thin thermalite/breeze block on top of a wooden beam
and plastered.

If I put a socket back box in one room, the back is in the other
bedroom, a right pain.