A floor slab is a poured concrete area designed for use as the foundational structure of a house. Floor slabs may be on grade with the ground, or they may be at the bottom of a hole and serve as the basement floor. On-grade floor slabs function in the place of a wooden floor, and remove the need for ground-floor construction of a joist framework for the floor.
A floating slab gets its name from the fact that it is not built on concrete walls. Generally, excavation for a floating slab involves digging down below the frost line or to bedrock, filling the hole with clean gravel, and pouring the slab on top of the gravel. The slab is reinforced with steel rebar, and made to be about 6 inches thick with a 12-inch thick footing around the edges. Because the clay and soil have been removed from underneath it and replaced with dry gravel, the floating slab doesn't move when freezing occurs.
Frost Wall Slab
A frost wall slab is similar to a floating slab with the exception that there are walls around the edges of the slab that extend down into the ground, either to below the frostline or to bedrock. These walls may be constructed of poured concrete or of concrete block. This construction system is often used in conjunction with heated slabs, because the frost walls make the entire construction easier to insulate in order to keep the heat in. Two-inch rigid foam panels can be affixed to the outside of the frost walls prior to the foundation being backfilled. After the house is built, these rigid foam panels can be extended up the exterior of the walls, creating a solid insulated barrier between inside and outside that extends down into the ground.
Radiant Heating Slab
A heated slab has pipes laid into it when it is poured. These pipes run back and forth throughout the slab, and can be connected either to solar hot water panels or to conventional water heaters. Hot water run through the pipes in the slab then heats up the entire slab, creating a very stable and draft-resistant heat for the home. The slab acts as a large thermal mass, trapping and holding the heat from the water pipes and releasing it slowly into the living space, regulating the highs and lows in temperature that are sometimes experienced with other heating methods.