How to Fix a Sagging Rafter


Sagging rafters are caused by the wood splitting or cracking in your attic. Repair rafters with faults as soon as you notice them to prevent ruining your roof decking, sheathing and shingles by water pooling in this area. Repairs to a sagging rafter shift the wood back into its original position and adds support to keep the rafter in place.

Things You'll Need

  • Ladder
  • Chisel
  • Drill
  • 1-1/2-inch-by-2-foot steel "L" channel (predrilled)
  • 2-3/8-by-2-inch lag bolts
  • Adjustable wrench
  • 2-3/8-by-4-inch lag bolts
  • 4-3/8-by-2-1/2-inch carriage bolts and washers
  • Place a ladder in the attic underneath the sagging rafter if you need additional height.

  • Remove any splinters or cracked wood on the rafter with a chisel.

  • Center a 1-1/2-inch-by-2-foot steel "L" channel over the crack so that four of the predrilled holes are on the left side and four predrilled holes are on the right side.

  • Insert a drill with a 3/8-inch bit into the four holes in the side that is hardest to reach. Two holes are on the side of the channel and the other two are on the bottom of the channel.

  • Insert a 3/8-by-2-inch lag bolt into each one of the bottom holes and tighten it with an adjustable wrench.

  • Insert two washers on two 3/8-by-2-1/2-inch carriage bolts. Install each carriage bolt through the top two holes on the same side of the "L" channel. Tighten the bolts with an adjustable wrench.

  • Insert two washers on two 3/8-by-4-inch lag bolts. Insert them into the bottom two holes on the other side of the crack in the "L" channel. Tighten each one slightly with an adjustable wrench until the washers are touching the "L" channel. Tighten the bolt farthest from the crack until a 1/4-inch crack appears between the front bolt and the "L" channel. Tighten the front bolt until it is flush with the steel. Repeat this sequence of alternately tightening the back and then the front bolt until the rafter is straight.

  • Insert two 3/8-inch-by-2-1/2-inch carriage bolts with washers through the remaining two holes in the top of the "L" channel and tighten them firmly with an adjustable wrench.

Tips & Warnings

  • Predrilled steel "L" channels are available at home improvement stores.
  • Chiseling off any splinters on the rafter allows the "L" channel to secure the wood tightly to bring it back to the original shape.

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