Build Subfloor Over Concrete Slab
Place the first layer with edges parallel to the longest starting wall.
Build subfloor over concrete slab. The underlayment exists to create an air filled gap between the concrete below and the subflooring which will help to insulate the floor and keep the room warmer. Subfloors are strong versatile and very durable. Install it flat on the slab surface with the outside edge aligned against the side wall or the edge of the floor line. Use a minimum of two layers 3 8 10 mm cd exposure 1 plywood subfloor panels cdx in 4 x 8 sheets.
Additionally the underlayment is always a waterproof material that will create a waterproof barrier. A subfloor will help insulate against a concrete floor that becomes overly cold in winter. Secure each length to the slab with concrete nails spaced approximately 32 inches apart and 8 to 12 inches from each end. You need a dry clean and flat surface before you can install finished flooring in a room built on a concrete slab.
While a subfloor is not necessary to add structural strength when you ll be laying finish flooring on top of a concrete slab as in a basement remodel subflooring over concrete offers two other advantages. These will be the end sill plates that support the ends of the floor joists. This may be as simple as a 6 mil polyethylene plastic covering 100 percent of the concrete and brought up all walls then trimmed after the floor has been installed.