The joists are at the bottom of your home's floors, followed by the subfloor and underlayment in the center and the actual flooring material at the top.
Joists
Everything above is supported by joists, which are the first and lowest layer of flooring. These beams form the "bones" of the floor, running from wall to wall. The joists that run the length of your house should be visible if your basement has an unfinished ceiling. Joists are typically made of 2x8 or 2x10 lumber in most parts of a typical house. Larger joists composed of dimensional lumber, laminated wood, or engineered wood are used when greater strength is required, such as when spanning long distances without a supporting wall. Except for concrete slabs, joists support every level.
Subfloor
The subfloor rests directly on the joists and acts as the foundation for both the underlayment and the visible flooring layers. The subfloor in a finished basement will frequently sit right on top of the concrete slab, with a thin layer of moisture separating the two. Your flooring specialists can glue new carpeting, laminate, hardwood, vinyl, or tile to the subfloor, which also provides a level, sturdy surface for you to walk on.
Underlayment
The third layer, known as underlayment, sits just beneath your selected flooring and above the subfloor. Because of the many advantages underlayment can provide, it is frequently used even if it is not a requirement. Underlayment can be made of a variety of materials, each of which has unique advantages. The underlayment is a finishing layer that can operate as a sound-deadening barrier, offer additional insulation against temperature fluctuations, or assist shield your flooring from dampness, while the subfloor offers structural support. Usually, it's just utilized to assist even out any warps or gaps in the subfloor material. This lessens any unevenness beneath hard surface flooring that may cause cracks or premature wear and stops any irregularities from being sensed through carpet.
Surface
