Most sheds are built with a construction technique that’s known as stick framing. The floors and walls are assembled out of individual “sticks” of lumber. (The term sticks refers to standard 2-by construction lumber.) Here, I’ll describe how to use the stick-framing method to build a sturdy, long-lasting floor frame for your shed.
Assemble the joists
The typical floor frame consists of three main parts: mudsill, perimeter rim joists, and floor joists. The mudsill is the lowest wood member in the frame; it sits flat on top of the foundation. The rim joists, also called band joists, frame the perimeter of the shed floor. The floor joists fit between the rim joists, on top of the mudsills, and are typically spaced 16 inches on center. For the best protection against rot and wood-boring insects, be sure to cut all the floor-frame parts from pressure-treated lumber. Most shed floors are framed with 2x6s and 2x8s. The correct size lumber to use will be clearly marked on your shed plans, but if you’re not sure – ask the local building inspector.
Fasten joists to the mudsill
The simplest way to frame the floor is to first fasten each mudsill to a perimeter rim joist to form a long L-shaped assembly. Set the mudsill assemblies on opposite sides of the foundation. Next, cut floor joists to fit between the two perimeter joists. Space the floor joists 16 in. on the center to provide the proper support of the shed floor. Nail or screw through the rim joists and into the ends of the floor joists.
Tip: Here’s a quick, accurate way to determine if the floor frame is perfectly square: Measure diagonally across opposite corners. If the two dimensions are exactly the same, then the frame is square. If not, adjust the frame until the two diagonal dimensions are equal.
Install the plywood
Once the floor is framed, cover it with plywood, which is easy to install, affordable, and surprisingly strong. Plus, the large sheets create a very smooth, flat surface, which makes it easy to roll, drag, and push objects across the floor. Use 3/4-inch-thick ACX plywood, which is exterior-grade plywood that’s well suited for use as a shed floor. Fasten the plywood to the floor joists with 1 5⁄8-inch decking screws or 2-inch (6d) galvanized ring-shank nails. And if you’ll be storing heavy equipment in the shed, consider using tongue-and-groove plywood, which locks together along the edges to create a rock-solid floor.
Tip: Make the plywood floor of your shed last longer and sweep up easier by applying two coats of enamel deck paint.