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How to Repair a Damaged Carrying Beam

Ask This Old House general contractor Tom Silva teaches a homeowner how to repair some structural problems in his home.

Steps for Fixing a Broken Beam:

  1. Use the jack and the temporary post to support the structure before removing any posts.
  2. Remove the old lally column with a grinder.
  3. Measure and mark the replacement column and cut it to size with the large pipe cutter.
  4. Smooth out the bottom of the new cut with a hammer and cold chisel.
  5. Put the post in place on metal plates and slowly remove the temporary post. Check the post for level before putting the full weight of the house back on it.
  6. Screw the metal plates to the beam and to the floor with the appropriate screws.
  7. To repair damaged beams, locate a local welder or metal shop and request angle iron, cut and drilled to the length of the beam being repaired.
  8. Remove any pipes, wires, etc. currently going through the beam. Be sure to turn off the water, power, etc. before doing so.
  9. Pry the joist hanger away from the beam.
  10. Mount the angle iron on the jack and the temporary post. Get the angle iron in place and slowly raise the jack until the angle iron is wedged up against the damaged beam.
  11. Screw the angle iron into the beam and remove the temporary post.
  12. Slide any pipes or wires previously removed back through the beam and turn the water and power back on.


Lally columns and the lumber used for the bridging can be found at the local home center or the local lumberyard.

Steel angle iron can be ordered to size and is sold at metal or welding shops.

Special assistance with this project was provided by Boston Welding.

In the workshop, Tom shared some basic rules for cutting and notching joists and rafters. For cutting holes, a hole can be no more than ⅓ the depth of the structure and cannot be within 2" of an edge.

For notches, the maximum notch depth is ½ the depth of the structure and no notches can be made in the middle ⅓ of the span.