Flooring is typically made up of several layers, beginning with the joists below, the subfloor / substrate, underlayment in the middle, and the floor covering at the top.
This is the visible floor, the one you see and walk on.Called a floor covering or finish floor, this might be ceramic tile, solid wood, laminate, engineered wood, luxury vinyl, carpeting, or others.
Not required to provide structural support, but often provides a type of supplementary support. When you remove the floor covering, you will see more flooring underneath—possibly underlayment, definitely subfloor.
Underlayment is the third layer, residing just above the subfloor. The underlayment serves as a sound barrier and can protect your flooring from moisture and heat.
For carpet, underlayment is used as the extra layer of comfort and can be used as a barrier for topical moisture. The only hard surface floor requiring underlayment is laminate. Underlayment can help protect laminate from moisture that may rise from below.
Subfloors or substrates are the surfaces on which floor covering materials are applied. They can be wood, concrete, plywood, stone or metal. The subfloor is the bottom-most layer and it rests on the joists. If you have a concrete slab floor the slab may be considered the subfloor.
Regardless of the material, there are specific preparation considerations that must be adhered to so that the installation of the flooring material will not be compromised. Subfloor not only makes it easier for installers to lay new carpeting, laminate, hardwood, vinyl or tile, but it also makes your floors smoother to walk on.
The subfloor acts as a foundation for both the underlayment and surface levels of flooring. A subfloor provides a stable, level surface that new flooring can be easily installed on. The subfloor is the thick flat surface on which all other layers rest.
Joists are the first/lowest layer of flooring and support everything above. Every floor has joists, except for concrete slabs. Joists are typically made of engineered wood, laminated wood, or dimensional lumber.
While not precisely a “floor layer”, joists are an essential part of the floor layering matrix. Joists are structural; they support everything above.