Monolithic or thickened edge slabs can only be insulated on the outside. In climate zones 4 and 5, building codes require a minimum of R-10 vertical insulation that extends 2 feet downward. In climate zones 6, 7, and 8, it should extend 4 feet down. The main disadvantage of the outer insulation of the base is that the part above ground level must be protected from physical damage.
Material options include a cementitious coating (ideally, one with chopped fiberglass), cement board, pressure-treated plywood, metal flashing, or a patented plastic or peel-and-stick cover (Protecto Bond). A 2-inch rigid foam insulation layer is forty times more efficient at trapping heat than concrete alone. Because concrete has the ability to retain heat and is more conductive compared to other building materials, such as wood, for example. Most inspectors, however, require that above-ground slabs be insulated in the same way as below-level slabs.
Although building codes differ by region, builders typically use R5 and R10 insulation under the concrete slab, but floors insulated with R20 contain basement heat much better than insulated ones with lower R values. On its own, a concrete floor will give you the minimum insulation you need to avoid inclement weather. Under-tile insulation will help prevent moisture, toxic fumes, condensation, mold and mildew, and even unwanted pests from entering your home. A 4-inch concrete slab has an R-value of 0.4, which is very low; heat escapes through the concrete very easily.
While concrete is a primary insulator against the elements, it won't help you much in extreme climates. The most laborious method to insulate a concrete floor is to build a subfloor on it and fill the space between the concrete and the floor with insulation. The most common types of underslab or concrete insulation include rigid foam insulation, such as expanded polystyrene (EPS), extruded polystyrene (XPS), and radiant insulation, such as Prodex. Since water from the ground absorbs into the rigid insulation over time, it is necessary to place a barrier between the foam and the concrete.
In very cold weather, the ground under the slab will be colder, and that cold will transfer to the concrete floor. According to Archtoolbox experts, the R-value of concrete varies depending on the density of the concrete mix.