How to Repair a Beam in an Older Barn


Antique barn timber is a very desirable building material. If the stress of holding the roof up has not caused cracks and the roof has stayed weathertight, the beams of an old barn will season well. The best way to repair damage to an old barn beam that does not show signs of rot and is otherwise sound is to lift it back into place, provide support from below and splint the damaged section with bolted steel repair plates on either side. For beams that are severely bowed or damaged in more than one place, consult a professional architect or carpenter to make sure the beam is safe.

Things You'll Need

  • Mason's twine
  • 2-inch-thick lumber
  • Treated deck screws
  • 4-by-4 posts
  • Screw-style post jacks
  • 6-by-6 posts
  • 1/4-inch thick steel repair plates
  • Drill
  • Bolts and hardware
  • Socket wrench
  • Shine a light along the length of the beam and mark the damaged areas with chalk to assess the scope of the damage. Drive a screw into the side of the beam 1 inch from the bottom, at each end of the beam, and tie a piece of mason's twine between them. Measure from the string to the bottom of the damaged area to determine how much the beam has sagged. If it is less than ¼ the height of the beam, you may proceed. For more severe damage, consult a professional.

  • Tack a piece of 2-inch-thick lumber as wide as the beam and a little longer than the damaged area to the underside of the beam with one 3-inch treated deck screw at each end of the board. Place a 4-by-4 post on top of a post lift jack under each end of the board. Screw the jacks up slowly, lifting the beam until the string indicates that the damaged area is even with the ends of the beam.

  • Dig a post hole directly under the center of the damaged area, 24 inches deep and 12 inches across. Place 2 inches of gravel in the bottom of the hole. Cut a 6-by-6-inch post to reach from the bottom of the hole to the bottom of the beam, plus 1/4 inch. Twist the jacks up far enough to slip the 6-by-6 post into place under the beam, with its bottom end in the post hole. Use a level to plumb the post front to back and side to side. Let the weight down onto the post.

  • Hire a welder to cut two 1/4-inch-thick steel panels as wide as the height of the beam and 24 inches longer than the damaged section. Drill holes 2 inches in from each corner with a 1/2-inch bit and along the top and bottom edges, 2 inches in, every 12 inches. Clamp the plates to both sides of the beam, centered on the damaged area. Use a square to mark the beams and align the plates on either side.

  • Drill through the pilot holes in the plates and through the beam to meet the holes in the plate on the opposite side. Drive a 1/2-inch-thick hardened steel bolt, long enough to penetrate the beam, and leave 3/4 inch on the outside of the plate. Tighten a washer and nut onto each bolt with a pair of wrenches. Twist the jacks down and remove the 4-by-4s to complete the repair.

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