Very often in older homes the existing floor joist may not have sufficient strength to support addition weight for remodeling. There are several ways to reinforce cellar or attic floor joists so the space above can be used for a bedroom, home office, or additional living space. Usually the best approach is to double up the existing joists.

This can be easily done by gluing and screwing a piece of lumber the same size to the side of the existing joists that are already in place. Make sure that the piece you installed is installed with its crown pointing up, and that it’s long enough to reach from the top plate of the outside house wall to the top plate of a bearing wall in the middle of the house.

How to reinforce floor joists:

If any of the floor joists are sagging more than 1/2 inches, they should be jacked up so they are as straight as possible. This can be done by wedging a 2x4 that is just a couple inches longer than the room is high under the bottom edge of the joist, and push it up until the joist is flat.
Spread a thick bead of construction adhesive along the side of the existing joist using a caulk gun. Apply a winding bead so both the top and bottom of each joist will be glued to the new joist.
Screw the doubled-up joists to the existing joist with 2 ½ inch long drywall screws. Drive three screws in a vertical line every 16 inches along the length of the joist. Then screw the floor plywood above to the top of the new joists.

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