Paddy,
Our house has a concrete slab above grade. The "low" side of our house is something like 18 inches above grade. The "high" side of the house is about 60 inches above grade. Now we have added fill dirt so those numbers are from the native grade not finished. On the "high" side of the house its 60 inches to the top of the slab. In other words our slab is a good 60 inches above grade on that side of the house.
The height really provides a nice view. I wished I had realized this would have happened cause I think we would have gone up another 8 or 16 inches in the foundation height to increase the effect even more.
I have not seen ANY house do this. It is not normal.
When the Directv installers showed up they walked around the house looking at the foundation for a crawl space access door. I was on the back of the house with the builder watching them literally scratch their heads looking for the access. When I told them there WAS not crawl space they looked at me like I was a space allien.
What the builder did was just build a regular foundation wall up from the footers. The wall is CMU faced with brick. Inside the wall we filled it with 67 stone. This is a stone up to and inch or so with NO fines. It compacts without mechanical means to the magic 90/95% number that engineers alway want. Before the 67 went in the plumber had put in his waste pipes. Then the stone went in. Then the two inches of ridgid foam was put in on top of the gravel with one inch around the foundation. Then the concrete was poured on top of the foam. I think the foam was EPS. I was very specific on that requirement since it could handle the PSI of the house sitting on top of it.
We also colored our concrete so that its a tan shade which has worked out nicely. Our floor is finished concrete. The color came out just right but around the edges of the floor its not like we would like since the motorized trowel could not get all the way to the edge of the floor due to the walls. But the mass and durability of the finished concrete has worked like we wanted. People thought and still think we are nut for have a finished slab but we can't stand the dirt that carpet holds. The floor is easy to clean and keep clean. If you get water on it you don't really care.....
We did have a plan that we used to cut the concrete to "decorate" it as well as guiding cracking. This worked real well for the most part. The only cracking we have had outside the cuts has been where the slab was stressed due to the shower stall and the front porch. We have a walk in shower with no door or "dam" to keep in the water. To get the shower built we made a form to keep the concrete OUT during the slab pour. This was done so the that plumber could make his final connections and so the tile guy could get his slope to the drain just right. This hole in the slab caused stress and even though we had cuts in the room the cracks went out at something like a 30 degree angle from the shower. The front porch cause a similar problem. The porch is about 16 inches below the house slab and is L shaped. The L caused stress and again even with the cuts there is a crack at that same angle. But they are not big deals And really are not noticable.
In the 19 months we have lived in the house we dont have one crack in the walls. The house has not settled at all and we have done through a couple of very dry and wet spells. We have an expansive clay but so far, knock on wood, it has not been a problem. Our old house in the "city" CONSTANTLY had cracks above the windows and doors due to the movement of the house. The house was on a slab as well with expansive clay.
We wanted a slab for a couple reasons. One the mass. Two durability. Three crawl spaces are a headache as far as I'm concerned. They can be mold and wetness magnets. If our old house had been on a crawl space I'm sure the bathroom floors would have had to have been rebuilt to to water issues. With a slab its not an issue. But crawlspaces in my area are the norm.
Our builder's next project was a light commercial building on a site where he had previously built a structure which used a crawlspace. The sister building had a concrete slab built on a "fill" on 67 stone.
Hope this helps,
Dan
