Sleeper Subfloor Installation

A sleeper subfloor installation will definitely decrease the height of the ceiling, but the subfloor will add additional insulation for the room or the entire home. The installation of the subfloor involves the laying down pieces of lumber to elevate the subfloor before actual installation of the subfloor material. The process is a bit time consuming, but nonetheless provides a rewarding experience.

Tools and Materials

  • Cloth
  • Oxygen Bleach
  • 2x4 pressure treated lumber (Sleepers)
  • Saw
  • Hammer
  • 2 ½-inch concrete nails
  • 5/8-inch OSB or plywood
  • Tape measure
  • Vapor barrier
  • Asphalt primer
  • Asphalt mastic
  • 1 ½-inch thick rigid foam insulation
  • Utility knife
  • Marker
  • Powder-actuated fasteners
  • Cedar shims
  • Spirit level
  • Drill
  • Screwdriver bit
  • 1 ½-inch flooring screws

Step 1 – Prep the Floor Surface

Remove dust and debris over the surface where the subfloor will be installed using a vacuum cleaner. Mix water and oxygen bleach in 50:50 ratio. Dip the cloth on the oxygen bleach solution and wipe it on the surface to remove remaining dust or mold buildup. Allow the surface to dry.

Apply asphalt primer and asphalt mastic. Follow manufacturer’s instructions on the manual during application. Cover the surface with a vapor barrier. Check the local codes for applicable vapor barriers allowed in your area. Examples include felt paper and polyethylene membrane. Spread the sheets all over the surface and allow them to extend at least 4 inches up on every wall surface.

Step 2 – Install the Sleepers

Plan a layout for the sleepers. They are called sleepers because they lay down on their flat side, instead of standing up on their short side, as in most applications. These pieces of lumber will be installed all around the edges of the subfloor and laid lengthwise from one side to the other, each piece spaced 16 inches apart on center from the others. The sleepers should follow the direction of the shorter length of the floor. Mark the lines from one side to the opposite side and make sure the spacing is exactly 16 inches on center. Determine the number of 2x4 boards needed to fit the layout. Cut the lumber accordingly.

Fit all pieces of lumber to conform to the layout – both on every edge and on the shorter length of the floor. Check the level of the pieces of lumber. Use cedar shims to make all top surfaces level. Use powder-actuated fasteners to fasten the shims to the substrate underneath. Drive 2 ½-inch nails into the sleepers every 24 inches, to fasten them to the substrate. Cut the extra sheets of vapor barrier on the edges before proceeding to the next step.

Step 3 – Insulate the Spaces in Between the Sleepers

Cut 1½-inch rigid foam insulation to fit the spaces. Fill every space with the insulating material and fit them snugly. This provides further insulation that will help save on energy costs on seasons with extreme temperatures.

Step 4 – Install the Subfloor Material

Determine how many sheets of plywood or OSB will be needed for the entire floor surface. Lay every sheet on top of the sleepers, and parallel to the shorter length of the floor. Cut the sheets to fit on the edges but leave a 1/8-inch gap to provide for expansion. While installing each sheet, fasten it to the sleepers using flooring screws. Drill the screws 12 inches apart from each other. Fit succeeding sheets joint to joint and secure them properly.