Replacing subflooring in a mobile home is necessary when there has been water damage or the home is so old that the subfloor is weak and crumbly in places. Most mobile homes have 3/4-inch composite wood for subflooring. It's stapled and glued to the floor joists beneath it. Joists are spaced 16 inches apart and run widthwise across the home. Subflooring is usually replaced only where needed, leaving secure flooring in place.
Locate a floor joist by sliding the stud finder along the floor, parallel to the length of the home. Mark where the stud finder first locates the joist and another where it loses the joist. Place a mark in the center between your first two marks. This is the center of the joist. Draw a continuous line across the subfloor showing the location of the center of the joist. You can check that the line is accurate with your stud finder.
Draw a rectangle or square that includes all subfloor to be removed. Lay the framing square on the corners and adjust the lines to follow the right angle of the square to get square corners. The side of the opposite the first line you drew should be extended to the center of the next available joist, so that there is a joist on both sides.
Set the circular saw blade to cut slightly deeper than 3/4 of an inch and cut along the lines. Use the reciprocating saw to cut in places where the circular saw won't reach. Use a hammer and chisel where neither saw will work.
Pry up the old subfloor with a pry bar and hammer. Areas between joists should come up easily. Old subfloor on top of the joists will require extra effort, but all the material has to be removed. The joists should be free of nails, staples and glue.
Use the circular saw and chisel as necessary to clean up the edges of your cuts. At least 3/4 of an inch of joist should be showing so you can fasten the new subfloor to it.
Cut the plywood replacement piece. Reduce each dimension by 1/16 of an inch so the piece will be easier to fit.
Test the replacement piece and trim it if it's too large. If it is too small, measure and cut a replacement piece.
Apply a bead of construction adhesive the length of the cut on top of the joists.
Set the replacement piece in place and screw it down to the joists. Space the screws 6 inches apart, on the center of the joists.
Caulk the cracks on all sides where the new piece meets the old subfloor.