Things You'll Need
6-mil polyethylene sheeting
2-by-4-inch pressure-treated boards
4-foot-long carpenter’s level
2-inch masonry screws
2-inch masonry drill bit
Sleeper joists are wooden boards installed on top of an existing subfloor that are typically used as support for hardwood flooring. The sleeper joists follow the same arrangement and spacing as the main home joists located under the subfloor. However, because the subfloor may have dips or depressions, you have to level out the sleeper joists before attaching them. You do this by using wood shims to create a perfectly level surface across the top of the entire joist system.
Remove all items from the floor and sweep it thoroughly to remove sand and debris.
Place a roll of 6-mil polyethylene sheeting at one end of the room 3 inches up the wall and unroll it until reaching the other end. Extend that end 3 inches up the wall and cut off the excess with a utility knife.
Install additional rows of the sheeting across the entire room, overlapping each row by 6 inches. Apply packing tape to all seams between the rows.
Walk to one side of the room and lay a pressure-treated 2-by-4-inch board on the floor 1/2 an inch from the wall and parallel to it. Install additional boards around the perimeter of the room in the same manner.
Lay the center sleeper joists by placing them all 16 inches apart across the surface of the floor. Ensure that the end of each sleeper leaves a 1/4-inch gap between the side boards. Cut the sleeper joists down using a circular saw if needed to create the necessary gap.
Place a 4-foot-long level on top of two sleepers so that it is perpendicular to them. Check the center air bubble to determine if the sleepers are even. If the sleepers are uneven, the air bubble will not center.
Apply a 1/4-inch bead of construction adhesive around the perimeter of a wood shim and turn the glue side toward the floor. Slide the shim under the sleepers until the air bubble is in the center of the level. Repeat the process across the entire floor to level all remaining sleeper joists.
Insert a 2-inch masonry screw through the center of each sleeper joist, using a power drill. If needed, predrill the hole with a 2-inch masonry bit prior to inserting the screws. Install additional screws every 16 inches along each board.