How to Fix a Broken Floor Joist
Repairing a Floor Joist with a Sister Joist
Correcting a problem joist is an easy repair and is usually accomplished by fastening a new joist next to a damaged floor joist. This is referred to as “sistering.”
When sistering cannot be accomplished there are a few other ways to reinforce a floor joist.
Plan Your Repair
This floor system was built in 1863 and was later reinforced with a mid-span beam approximately 7-feet away. The damaged joist measured exactly 2 inches by 6-1/4 inches deep, a true 2×6.
My approach was to install a new joist next resting one end 3-inches onto the mid span beam and installing a joist hanger on the other side. I would sister the two together with structural screws.
The space between the beam and the floor boards above was 7 inches so I decided to use regular framing lumber and rip a 1’2-inch on the width of a 2×8 framing member. Note – A 2×8 board measures 1-1/2 by 7-1/2”.
