Good subfloors make solid structural foundations
Subfloors are one of those construction features that earn very little attention unless there's something wrong with them. A good subfloor is one of the keys to a secure structural foundation. It is the layer of flooring that directly supports the top layer--traditionally carpet, tile or hardwood. A subfloor can be made from CDX 3/4-inch tongue-and-grooved plywood or 3/4-inch-thick-by-4-to 8-inch-wide, southern yellow-pine boards. Many contractors will also include a layer of 15-pound, black felt hardwood flooring underlayment paper to serve as a moisture barrier to protect delicate top flooring layers.
One of the primary benefits of a quality subfloor is its ability to smooth out previously cold and irregular floors. For the top floor, the surface is comfortable to walk on and the climate is easier to control. For the space below, such as a basement area, it allows the area to be finished off and made into a useable living space.