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How to Fix a Bowed Rafter

Mike Johnson

A bowed roof rafter in your home can cause serious problems that might become irreversible if you don't do something about it right away. When the roof rafters are bowed, they will begin to sag. With enough sagging, you will be looking at foundation and structural damage that will likely need to be repaired by a professional contractor or even a structural engineer. However, in the beginning stages of this issue, you can opt to fix the bowed rafter yourself and save a lot of hassle in the future.

  1. Drill holes into a piece of 1.5-inch by 1.5-inch steel L channel. The L channel should be a minimum of 2 feet long to fix the bowed rafter. Use a diamond-tipped drill bit and power drill to make four 3/8-inch holes on either side of the L channel. The holes on either side should be staggered from each other.

  2. Use a chisel to remove any splinters on the bowed rafter. These splinters can get in the way of your repair.

  3. Attach the four holes on the right end of the L channel using 3/8-inch by 2-inch lag bolts and your power drill. Note that you are first attaching one side of the L channel so that it fits straight across the sagging rafter.

  4. Measure the gap between the bent rafter and the other end of the L channel that you have not secured to the rafter yet. Choose an appropriately sized 3/8-inch diameter bolt. The bolt needs to be 1.5 to 2 inches longer than the gap you measure.

  5. Put the lag bolts in place and start tightening. As you tighten, the bowed rafter will slowly start to straighten out as the bolt gets pushed into it.

  6. Continue installing lag bolts in the three other holes in the L channel. By the time you're finished, the bowed rafter will be straightened out and reinforced by the steel L channel.