How to Frame a Wood Floor

Cut the outside boards of the frame from 2-by-4-inch planks using a circular saw. For a 10-foot-square floor, you’ll want to cut two of the boards 10 feet long and two 9 feet 9 inches long.

Place the boards onto a flat surface on the 2-inch edges. Position the two longer boards parallel to one another with the shorter boards placed between them at the ends. Make certain that the ends of the adjoining boards are flush with one another, and check that the inside angles are 90 degrees using the carpenter’s square. Place a carpenter’s level across the adjoining boards to make sure they’re level as well.

Nail the boards into place with a framing nail gun to form a square. Set a short board inside your square between the long boards every 16 inches to form the floor joists of the frame. Make certain the boards are square and level, and then nail each board in place with the framing nail gun.

Install cross braces into the spaces between the floor joists to provide extra strength to the floor frame. Cut five cross braces from a 2-by-4-inch plank 14-1/2-inches long to fit within each joist space. You'll want to place the planks so that they create a staggered appearance between spaces, offsetting the position of the braces from one space to the next to avoid creating a straight line of braces across the floor. Place a plank every 16 inches lining the first space, and then nail them into place. Move the boards off-line 3 inches in the next space, and then nail them into place. For the third space, place the line of boards in the same position as the first line and nail into place. Move the boards 3 inches off-line in the opposite direction as the second space for the next empty area and nail into position. Repeat the pattern to have a staggered board spacing for the cross braces.