How to reinforce sagging beams

Written by nicola gordon-thaxter
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How to reinforce sagging beams
Don't leave sagging beams alone-reinforce them as soon as possible. (Stirling Castle Great Hall image by luapeed from

If buildings aren't constructed properly, over time ceiling or floor beams may sag. This can lead to a building being unstable, which can put you and your family at risk of serious injury. To avoid a sagging beam from worsening and collapsing a ceiling, it needs to be reinforced. You can reinforce a sagging beam with a hydraulic floor jack, some wood beams and some epoxy or glue. If you reinforce in good time, you can avoid the disruption that comes with broken beams.

Skill level:

Things you need

  • Hydraulic floor jack
  • Two two-by-four beams
  • Two, 20-foot two-by-twelves
  • Two 1/2-inch diameter by 20-foot-long steel rebar
  • Drywall screws, approximately 10
  • Screwdriver
  • Epoxy
  • Router
  • High density filler
  • Caulking tube
  • 2 or 3 large C-clamps

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  1. 1

    Screw the two two-by-four beams together to make one post.

  2. 2

    Place the hydraulic floor jack beneath the sagging beam. Position it in the middle of the beam, then brace the post between the jack and the sagging beam.

  3. 3

    Jack the sagging beam up slowly, over the course of three or four days to raise it back into place. Jack the beam up a little bit each day until it is completely up: This enables the building to adjust to the movement of the beams.

  4. 4

    Prepare the two 20-foot two-by-twelve beams, which will be what Jamestown Distributors calls "sister beams." Use the router to carve a 3/4-inch wide by 3/4-inch deep groove down the centre of the bottom edge of the beams. Sand the inside of the groove to help the epoxy penetrate.

  5. 5

    Spread unthickened epoxy into the groove using the caulking tube, then on top of that spread a bead of epoxy thickened with high-density filler.

    How to reinforce sagging beams
    Spread the epoxy onto the wood using a caulking tube for evenness. (glazier image by Greg Pickens from
  6. 6

    Lay the rebar into the groove on top of the epoxy and smooth any excess epoxy down. In the places where the rebar doesn't sit nicely into the groove, use the drywall screws on either side of the bar to sink it properly into the groove. The steel concrete reinforcing bar, or rebar, is sunk into the groove to strengthen the beam and avoid it sagging in the future. Let the epoxy dry for about three days.

  7. 7

    Sand down the sagging beam.

  8. 8

    Spread thickened epoxy onto the horizontal surface of the sister beams and stick them onto the now straightened beam that was sagging.

  9. 9

    Clamp all three beams together to ensure it all holds and then remove the jack and the clamps once you are sure the epoxy has cured.

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