How to Install Subflooring for a Wood or Concrete Floor
Find out what subflooring material works best with a variety of flooring, then learn how to install it.
Plywood is the most common type of subfloor in new homes. Plywood is rated for use, based on whether it’s for interior or exterior applications and what type of material you plan to use for the finished floor. Available in standard sheets of 4' x 8', a thickness of 5/8" or 3/4" is recommended. Tongue-and-groove plywood works best for a subfloor because it'll help protect against moisture and movement.
Your work will be easier if you minimize the number of cuts you need to make to cover the floor. Lay out your floor carefully before you start attaching sheets to the joists. Also, plan the layout so that the cut edges are against the perimeter of the room. Make sure the sheets are spaced evenly and butt each sheet tightly.
Layout the boards before securing them to the joists, this way you can minimize the number of cuts. Find the center of the floor with a tape measure and align the first sheet as close to the center as possible. Snap a chalk line or two to help with alignment. Starting in the center of the room, lay sheets of plywood across the floor joists. Make sure the edges parallel to the joists fall on the joists. In addition, make sure that the sheets are staggered and spaced evenly. There should be no corners where four sheets come together. Lay the plywood with the grain running perpendicular to the joists and the better side facing up. Leave about 1/8" between the walls and the plywood to allow for expansion.
To cut plywood to size, use a pair of sawhorses and 2x4s to create a stable cutting station. Use a circular saw with the depth of the blade set a 1/2" deeper than the plywood sheet.
Lift up a section at a time and apply a consistent bead of construction adhesive on the floor joists. (This will help prevent a squeaky floor after the finished floor is installed.) Lay the plywood back down inserting the tongue into the groove joints of each piece of plywood. Use an extra piece of lumber as a smash block to protect the plywood tongue. Smash the additional pieces of plywood in place so they are joined together tightly.
Secure the boards with nails in every six inches along the joists. Screws or staples may also be used.
Remember to keep the wood about 1/8" away from the walls to allow the material to expand.
If you have sheets that don’t land securely on a joist, use blocking to create extra support. Use at least a 1x8 board to create the board and secure it to joists with nails.
Check each sheet of plywood to make sure it is level. If a sheet is raised, drive extra staples (or nails) to force it into place.
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