Just remembered that all the Levittown communities built post war were on cement slabs...Larry
My house in Milpitas is on a cement slab. Built 1962. They called the development area Milford Village. It was created to serve the military station personnel at Moffet field about 10 miles away. It wasn't the first development area for this purpose.
As you might expect, they weren't high dollar luxury homes. But, something to entice lots of VA loan guarantees. The homes were Eichler inspired downsized floor plans without all the glass usually incorporated in Eichler designs. Milpitas building codes allowed a concrete slab on a footer 1 foot wide by 1 foot deep at each load bearing portion of the building frame. They built a lot of these homes. And a lot developed problems, including mine. I simply didn't notice the early signs in 1975.
The west coast of California was once sedimentary ocean floor bottom which got pushed up above water, by the pacific plate getting pushed under the continental plate. My house is located near the foot of a 500 Ft ridge, on soil that is designated alluvial. Alluvial soil is good for many things, but stability is not it's forte. It absorbs water readily and expands when doing so. It also contracts when the soil drys out. No big deal unless a weight is put on top of it. As it drys out, it sinks in elevation and the water leaves. When it gets wet again, it expands back to its previous height lifting what is on it some but also expanding out sideways.
We have a 4 - 6 month wet season here, and a 6 month dry season. My unirrigated back yard will form numerous deep cracks 1/2" wide by September, and disappear completely within two weeks at start of rainy season. This sets up a yearly swelling/contracting action of the soil under the house, each year losing about an eighth of an inch about the perimeter of the house under the load bearing walls. After 30 years of 1/8 elevation loss yearly about the perimeter, the external walls and floor, had sunk two and a half inches, whereas the center of the house slab and support walls had not. The ridge line of the roof had pulled apart 1/4 to 1/2 inch under the movement forces. You could actually feel yourself walking down hill walking from center of house toward an outer wall.
How do you fix the foundation of a slab floor house? I had several contractors give me estimates from $15000 up to $30000 1989 dollars. Schemes from lifting the whole house and replacing the footer and 6 ft of slab about the perimeter back to proper grade. Jacking the house, drilling and installing 25' columns of rebarred concrete, effectively placing the house on stilts buried in the ground, as well as "mud jacking", where they pump concrete under pressure into the ground through holes drilled in the slab, to raise the soil and house above it. I've seen some of these solutions applied to other houses in this area. All required the house to be vacated during the repair process and none would guarantee that the problem would not come back!
To their credit, they did teach me that the root cause was "alluvial soil" and a foundation that did not go deep enough to reach the stable soil under it. The alluvial soil at my building site is about 2 ft deep, meaning the required "footer" was about a foot away from reasonable stability. I wondered why the local building codes allowed this flawed construction scheme to proliferate. I speculate that the permit and inspection fees weren't affected by this oversight.
I tell you this because it proves that the existence of slab floor houses built in your area, does not necessarily mean they are structurally stable. Personally, I would not trust one in a frost heave area without knowing by what mechanism they can resist the forces of nature. So I ask, how did they keep the slab floors and foundation stable for those houses, or did they just let the home buyers fend for themselves?
