How to Fix a Sagging Floor Joist

Sagging floor joists may be due to weakened or rotting wood.

Sagging floor joists can be an annoying problem and a major structural defect. Weakened floor joists may come off of the flooring material, causing squeaking or a bouncy floor. Severely weakened joists, if not fixed early, can even break entirely, causing sunken sections of the floor above or even floor collapse. Sistering joints is a way of adding another, stronger joist to the sagging portion for extra support without removing the old joists, which can put the floor above in danger of collapse.

Things You'll Need

• Lumber
• Saw
• Construction adhesive
• Hammer and nails

Instructions

1. Measure the length and width of the sagging floor joists with a tape measure.

2. Rip a piece of lumber the same size as the old joist with a saw or ask for a custom-cut piece from your local lumberyard.

3. Spread construction adhesive onto the side of the sagging joist.

4. Press the new piece of wood against the joist, butting the top of the new piece to the floor above.

5. Drive three nails, moving from the top to the bottom of the two joists every 16 inches, to secure the new joist to the old one.

References

• Home Addition Plus; Sistering Floor Joists -- How to Remove Floor Bounce by Sistering Floor Joists; Mark J. Donovan
• Hammer Zone; Sistering Floor Joists; Bruce W. Maki
• The Family Handyman; How to Make Structural Repairs by Sistering Floor Joists; August 2006