- 1). Remove the main floor and sub-flooring using the hammer, pry bar and cold chisel. If you have a hardwood floor, slip the pry bar between two joints of wood and pry them loose, extracting them one plank at a time. If you have tile, crack the grout using the hammer and cold chisel, then pry the tiles up by placing the tile arm beneath the tile, striking it with the hammer and loosening it a bit at a time until the entire tile comes free of the tile glue.
- 2). Pry the entire panel of sub-flooring plywood up using the pry bar. This will expose the joist, which you need to replace in its entirety.
- 3). Pry the floor joist horizontally away from the header joist beneath the wall, from all center girders, and from the opposite wall's header joist using the pry bar. The floor joist connects to the header joists beneath the wall, and the joist itself rests on one, maybe two (depending on room size), central girders.
- 4). Measure the damaged joist length with your measuring tape.
- 5). Cut the replacement 2-by-4 joist to a length that matches the damaged joist using the circular saw.
- 6). Set the replacement joist in perpendicular along the girder between the other joists.
- 7). Screw the joist into the header joist using the power drill and the 3-inch deck screws, positioning the screws 2 inches apart in the shape of a triangle at each end of the replacement joist. Although you'll find the original joist was connected by nails, you can't nail into the header joists because they are under the wall, and you won't have room or leverage. Additionally, the screws will create a tighter hold than nails.
- 8). Replace the sub-flooring using the hammer and nails. Position the nails approximately 1 inch from pre-existing holes.
- 9). Replace your main flooring using wood glue for hardwood floors and quick-set tile grout for the tile.