Crawl spaces, basements and slabs are the main three foundation systems used to build houses. In coastal and wet areas, sometimes it is common to put such foundations.

Probably the slab is the easy foundation to build. It is a flat concrete pad directly poured on the ground. It takes few labor to create, site preparation and formwork for the concrete. It works very well on the level sites in warm climates. It has few problems regarding north side due to freezing of ground level in the winter. This freezing can move the slab at worst and lead to cold floors in the winter. The cross-section of the typical slab looks like this.

Beam of the concrete

At the edge of the slab, the concrete forms a beam perhaps whose depth is about 2 feet. The thickness of the remaining slab is about 4 to 6 inches. The layer of 4- or 6-inches of gravel lies under the slab. A 4-millimeter sheet of plastic will place in between gravel and concrete to keep moisture out of it.

It is embedded in the concrete for 6-inch by 6-inch wire mesh and steel reinforce bars is found at the bottom of the beams. Often you will heard that this kind of foundation known as a “floating slab”. It floats on the soil, with deep concrete around the edge holding it in place. In northern climates, the concrete found around the edge has to extend deep enough to remain below the frost line in winter.

Bottom Line

The important thing about the slab is that the sewer pipe, and sometimes the electrical conduit, has to be keep in place before the concrete is poured. Actually the sewer pipes are embedded in the slab.