Moisture

• Basements often collect excessive moisture and putting in a subfloor can help alleviate difficulties that this can cause. Condensation can collect on the concrete floor and potentially contact and damage the finished floor. Installing a subfloor creates a barrier between the moisture and the floor finishing material. Subfloors do not solve serious leaks, however. For serious moisture problems you may need to install a footing drain or a sump pump before putting in a subfloor.
  
  

Solid Base

• Many basement concrete floors have rough and uneven patches that can make putting a finished flooring material directly on top of them problematic. You may have to perform an extensive repair to the entire concrete floor surface with a liquid product called a floor leveler to produce an acceptable base for the finishing material. A sound subfloor covers minor irregularities in the concrete and not only provides a solid and even base, but also provides a softer and more comfortable feel for anyone walking on the finished floor.
  
  

Types

• The traditional method of installing a subfloor uses a combination of wooden boards and plywood. You place the boards over the concrete base and nail the plywood to the boards. A more recent type of subfloor uses 2-by-2 panels that have an engineered wood product attached to a moisture barrier. The system may use tongue-and-groove joints to connect the panels. You determine the number of panels needed by dividing the room's square footage by 3.3.
  
  

Headroom

• On reason in the past not to put in a subfloor was because it could reduce needed headroom. The traditional method of using boards and plywood may take away 2 inches or more from the room's height. If the basement height was already low, this may make a subfloor unacceptable. The new panel systems, however, usually take up less than 1 inch of space, mitigating any concerns about the loss of headroom.