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How to Repair a Cracked Floor Joist | Ask This Old House

This Old House general contractor Tom Silva helps a homeowner repair a cracked floor joist.
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Shopping List for Repairing a Cracked Floor Joist:
– Carpenter’s glue, used to mend cracked joist
– Old-work joist hanger with hanger nails, used to support end of joist
– Cloth, for wiping off excess glue
– 1x3s, used to make cross-bridging
– 2x lumber same size as floor joist, used to make solid blocking
– 3/4-inch plywood, used to reinforce a notched joist
– Nails and construction adhesive, for securing the plywood strip

Tools List for Repairing a Cracked Floor Joist:
– Hydraulic jack and 2×4 post, used to jack up the cracked floor joist
– Hammer
– Caulk gun, for applying construction adhesive

Steps for Repairing a Cracked Floor Joist:
1. Squeeze a generous amount of carpenter’s glue into the crack in the floor joist.
2. Slip an old-work metal joist hanger onto the end of the joist.[BR] 3. Position a 2×4 post and hydraulic jack directly beneath the cracked end of the joist.
4. Pump up the jack until the post pushes closed the crack in the joist.
5. Fasten the hanger to the beam with hanger nails.
6. Use a cloth to wipe off any excess glue from the joist.
7. Install cross-bridging or solid blocking between joists to help stiffen the floor.
8. When notching a joist, all notches should fall within the first or last third of the joist. Never cut a notch into the center third of a joist.
9. The depth of the notch shouldn’t be more than one-sixth the height of the joist.
10. The length of the notch shouldn’t be more than one-third the height of the joist.
11. Notches should be cut straight and clean with radiused corners.
12. Reinforce a notched joist by attaching a 3/4-inch plywood strip.
13. Cut the plywood strip at least as wide as the joist and secure it with construction adhesive and nails.

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

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How to Repair a Cracked Floor Joist | Ask This Old House


  1. Drywall screws are weak because they fasten light drywall, but framing screws are for lumber.

  2. lol the panic in her voice. you can tell he's a good contractor by how he soothed her nerves with that explanation.

  3. Why do all the joists and such look charred? Was there a fire or is that some sort of treatment?

  4. What changed in 8 years?

  5. My God, the placement of the refrigerator is crazy.

  6. Those jar lids on the beam, old-school.

  7. 6:17 poor building logic. They didn't follow the adding rule where every piece, going down the hierarchy is dimensioned bigger than the last one. You never hang a large piece of lumber on a small piece of lumber, it does nothing.

  8. Excellent video. Thank you!

  9. Does Tommy’s formula work for outside deck joists as well? Or does pressure treated lumber different than standard lumber?

  10. I know this is an old video but can you use lag screws to attach the sister board? Something like a Spax powerlag screw or GRK structural wood screw as options

  11. Legend says that tape rolled all around the world.

  12. If only my house was built in a standard American way. I don't believe it ever had any level floors to begin with.

  13. omg a ghost moved the round thing

  14. Who can I hire to repair my floor joist? A handyman, carpenter, contractor? I don't find much information on Google

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