How to Replace Foundation Floor Joists

A wet crawl space, mold and pests can all cause foundation floor joists to rot and become unsafe. While repairing the joist is often an option, there are instances when the joist is too damaged for repair and must be replaced. If you aren’t afraid of getting dirty, this do-it-yourself job is possible with the help of a few tools from your local hardware store.

Measuring tape
Boards the size of the joist
Circular saw
Joist hangers
16d nails
2 Hydraulic jacks
Reciprocating saw
1-inch hanger nails
Hammer
2-by-6 board

Instructions

- 1
  Enter the basement or crawl space and locate the rotten or damaged floor joists under your home.
- 2
  Measure the joist you're replacing. This helps determine the size necessary for the new joist.
- 3
  Cut the new 2-by-8 or 2-by-10 boards -- whichever matches the original joist size -- with a circular saw to match the lengths of the joists removed.
- 4
  Attach the joist hangers to each end of the new joist by slipping the hanger under the end of the joist. Hammer 1-inch hanger nails into the four pre-cut tabs to hold them in place.
- 5
  Line the joist up along the side of the old one and attach the joist hangers to the framing with the 16d nails. Secure them with two nails on each end.
- 6
  Place a hydraulic jack, with a piece of scrap wood on top, beneath each side of the old joist. Raise the jacks slowly and release pressure from the joist.
- 7
  Remove the damaged joists by cutting them with a reciprocating saw and tapping them with a hammer. Add a replacement brace under the joists by cutting a 2-by-6 board to the length of the joist to the ground, then wedging it in place.

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