My house is a very unusual Eichler. It has original forced air radiant heat. A forced air furnace pushes hot air through the slab, where it heats the slab and exits via floor registers located in every room. From what I can see peeking down the registers, the slab contains rows of U-shaped metal beams in two layers. In the bottom layer, the beams are oriented like a U. In the upper layer, the beams are oriented like an upside down U. The beams in the two layers run at right angles to each other, thus supporting the weight of the top part of the slab and the house. The U shape provides the empty space for the heated air to pass through.
I am curious to know whether anyone has heard of other houses constructed this way and perhaps knows more than I do about their construction. I will soon be posting a message on the Home Maintenance Hotline forum that will explain why I am interested in this topic right now. :(
The description I gave in my previous message is not quite right. I took another look just now, and what I saw were voids with steel supporting the slab above the voids. The steel does appear to form U-shaped channels, meaning that the slab above the void varies from 3" to 4" in thickness, and the void varies in height from 1" to 2". I saw only an occasional support under the steel. The voids appear to fill the larger rooms.
In addition, there is an 8" deep and 3' wide channel running along the entry way (at the back of the courtyard) leading to the bedroom wing.