How to Level a Bowed Floor
Floor joists may bow or sag because of exposure to water or humidity, causing the flooring they support to bow or tilt lower than the surrounding flooring. Fortunately, leveling a bowed wood floor is a straightforward procedure once you know which floor joist is warped. Once you've identified it, brace the sagging joist with a sister joist that raises it to the correct level, thereby leveling the bow in the floor. Work from the basement where you can easily identify and support the damaged joist. Does this Spark an idea?
Things You'll Need
- Measuring tape
- Handsaw
- 4-inch-by-4-inch post
- Hydraulic jacks
- Level
- Construction adhesive
- Caulking gun
- Hammer
- 16d nails
Instructions
-
-
1
Measure and cut a sister joist the same dimensions as the bowed joist, using a handsaw. If pipes, ducts or other obstructions prevent the sister joist from running the entire length of the bowed joist, cut it so it runs 3 to 4 feet on either side of the bow at the least when installed.
-
2
Extend the measuring tape perpendicularly along the span of three floor joists, with the bowed one in the middle, and calculate the length. Measure and cut a 4-inch-by-4-inch post to that length with a saw.
-
-
3
Set a hydraulic jack under each corner of the post and position this assembly under the three joists. The middle joist is the bowed one you want to repair. Crank the hydraulic jacks so the top of the post falls just below the joists. Set the sister joist alongside the bowed joist and continue to crank the jacks until the post falls flush against the undersides of the joists.
-
4
Crank the jacks up by just 1/8 inch every day so they gradually straighten out the bowed joist. Because the lifting process is gradual, it will not cause cracks in the flooring or drywall. Periodically hold a level on the floor surface to determine whether the bowed joist is level, so you know when to stop.
-
5
Attach the sister joist to the middle floor joist when it is leveled. Insert a tube of construction adhesive to a caulking gun. Insert the tip of a nail through the end of the tube to break the seal.
-
6
Spread the adhesive to any side of the middle floor joist in a zigzag pattern, until the entire length is covered.
-
7
Press the sister joist next to the glued side of the middle joist before hammering a series of 16d finishing nails through the sides to secure them together, spaced 16 inches apart. Ensure the nail heads are flush with the surrounding wood surface.
-
8
Lower and remove the two hydraulic jacks so the sister joist supports the middle joist.
-
1
Tips & Warnings
Before repairing the bowed floor yourself, call a structural engineer to inspect the extent of damage and determine whether the problem requires professional repairs. While some floor sags are easy to repair, those under a weight-bearing column or wall warrant professional assistance.
Predrill pilot holes in the sister joist and drive 3-inch-by-3/8-inch lag screws as an alternative to hammering 16d finish nails.
