A DIY Shed Floor

Lay out the basic dimensions of the shed with a tape measure and stakes and builder's twine. Square the outline by measuring diagonally and adjusting stakes until those dimensions are the same. Excavate the shed area with a shovel at least 6 inches deep for a slab or gravel foundation shed floor. Lay a moisture barrier on the ground for a gravel base. Fill the outline with gravel and compact it with a hand tamper. Build wooden forms and pour concrete, leveling and smoothing the concrete for a slab foundation floor.

Set concrete blocks or piers at the corners, in the middle of each wall and in the center of the shed for a wood platform floor, or lay wood beams or skids on a gravel foundation, facing in the long dimension of the shed. Use a tape measure to make sure piers or skids are properly spaced, and lay a long board with a level on it to level the tops of the piers, blocks or skids.

Build a frame of 2-by-4-inch lumber, nailed at the corners with 16d framing nails. Put the front and back boards across the ends of the longer side boards. Measure the width of the shed frame and cut 2-by-4 joists to fit. Install joists across the frame, spaced either 16 or 24 inches apart, either nailing through the side bands or using metal joist hangers fastened to the side bands to hold the joists.

Set the frame on the blocks, piers or skids. Use a 4-foot level to make sure it is level in all directions. Adjust the blocks, piers or gravel foundation by shifting the dirt or gravel, or use wooden shims under the outer band boards to get the top level.

Cover a wood-framed floor with 5/8-inch or 3/4-inch plywood. Use the thicker panels for sheds that will house heavier objects such as garden tractors. Run plywood with the top grain across the floor joists. Use tongue and groove plywood for a stronger connection between panels. Cut panels with a circular saw to fit the shed dimensions as needed. Fasten plywood to the outer bands and floor joists with 8d galvanized nails and a hammer or with 1 1/2-inch galvanized screws installed with a screw gun.