Removing and replacing floor joists can be costly and time-consuming. Here are some alternatives to floor joist replacement that will save money and keep you from tearing up the entire floor.
"Sistering" is the process of installing a second joist to each existing joist and is the best method for reinforcing an existing floor. There are 2 ways to sister joists; using the same size material and using one size smaller.
Sistering same size joists. In many cases, the existing floor joists can be reinforced by installing the same size joist. This is the best way to straighten a sagging floor. Each joist must span the length of the wall plates. This will be a physical task and a sledgehammer will be required to get each joist to snug in flush with the existing joists. Once in place, heavy-duty construction adhesive and 3-inch deck screws or Timberlocks should be used.
Sistering smaller joists. In some cases, you can sister smaller joists to the existing ones. For example, if you have 2 by 10 joists, you can install 2 by 8 joists alongside each one. By using one size smaller, you will have equal structural integrity, but it will not straighten the existing floor, only reinforce it. Again, each joist must span and rest on the wall plates.