How to Build a Subfloor with OSB

Substituting OSB in place of regular plywood is a great way to cut costs if you’re building a subfloor yourself. OSB (Orient Strand Board) is made up of hundreds of individual fibers that are laminated together to form one single sheet of material the same width, length and thickness of traditional plywood. Most importantly, it offers the same strength and support as plywood and is commonly used in new home construction.

Working with this material is just as easy as working with plywood so you’ll need the following tools and materials to get started:

  • Circular Saw
  • Tape Measure
  • Drywall Square
  • Four Foot Level
  • Saw Horses
  • Caulking Gun
  • Sub-Floor Adhesive
  • 2 Inch Coarse-Thread Screws
  • Cordless Drill/Driver
  • ¾  Inch 4x8 OSB

Step 1 – Layout and Cut the OSB

To begin you’ll need to check the subfloor framing to make sure its level so each seam will be flush and even. After a quick check, lay out the OSB so that it runs perpendicular to the subfloor framing. It’s also important to stagger the seams as well. To do this, measure the first cut so that the butt seam of the OSB board falls on the mid-point of the floor joist that’s closet to 48 inches. Set up the board on the saw horses and make mark the board with the dry wall square. Then make a straight cut using the circular saw and lay the board in place. Next, measure the distance to the mid-point of the floor joist that’s closest to 96 inches directly adjacent to the first board. Mark a new OSB board and make the cut using the circular saw. As you fill in the length of the room with full sheets keep alternating cuts for new runs as you move across the room.

Step 2 – Install the OSB

Once you’ve made the first two cuts and checked the layout you can now install them in place. Lay down a medium sized bead of sub-floor adhesive using a standard caulking gun. Then place the first board you cut and make sure its firmly in place. To fasten the board, use the drill or driver to install a 2 inch screw ever eight inches along every joist. The combination of adhesives and traditional fasteners help prevent squeaking over time.  Grab the second cut board and lay it down in place making sure it forms a tight seam against the adjacent board. Repeat the installation process using more adhesive and 2 inch screws. Now just fill in each row with full sheets of OSB repeating the steps of applying adhesive and then installing the coarse thread screws. When you get to the end of the room and have less than a full board, just measure the distance and make the cut with the circular saw.