How to Fix a Cracked Rafter in Your Attic

Your roof's structure is supported by multiple rafters that run across the width and length of the roof. While they are usually sturdy enough to handle most blows and loads, rafters will occasionally crack. Incidents such as storms and even walking across a roof surface can introduce a crack into a beam. If left alone, a cracked rafter permits the roof to sag, and this can result in costly leaks or other damage to your home.

Fortunately, repairing a cracked rafter isn't difficult and requires only a few basic tools and inexpensive materials. Below is how you can correct the problem and restore your broken rafter's structural integrity through roof repairs.

Tools and Materials Needed

  • Splint board—You will need to obtain a 2x6 pine board in a length that extends past the length of the crack plus an additional 12 inches. For example, for a cracked rafter that contains a 35-inch crack, your board should be at least 47 inches in length. Additional length is acceptable as long as the space is available for installation.
  • Hex-head bolts with matching nuts and washers—Purchase ¼-inch diameter bolts in 4-inch lengths; it is not important if the threads extend all the way down the length of the bolt, so buy whatever is available or the least expensive. You will need 2  bolts for every 4 inches of cracked rafter. For example, if the crack is 48 inches in length, buy 24 bolts with matching hardware.
  • Fender washers—In addition to bolts, washers and nuts, you will need to buy 2 fender washers for each bolt purchased. The fender washers should be at least 1 inch in diameter.
  • Alignment board—Buy a 2x4 pine board at least 8 feet in length.
  • Cordless electric drill with 5/16-inch bit
  • Lantern or headlamp, if your attic is poorly illuminated
  • Ratchet and socket set
  • Adjustable wrench
  • Hammers
  • 2-inch nails
  • Magic marker
  • Measuring tape


1. Force the cracked rafter into position. Before attempting a repair, the cracked rafter should be restored to its proper position. Much like a physician sets a broken bone, you will need to "set" the broken rafter by using a 2x4 board.

To do so, locate the center of the 2x4 board and nail it into the approximate middle of the cracked rafter from its underside. Next, nail the 2x4 board into the adjacent rafters on both sides. This action will push the cracked 2x6 upward and relieve the downward pressure caused by the crack.

2. Attach the splint to the cracked rafter. Once the original alignment of the cracked rafter is supported by the 2x4, nail the 2x6 splint board to the side of the cracked board so that all edges are flush. Be sure the splint board covers the entire cracked portion of the rafter. Only use a few nails to attach the board since they are temporary and can be pulled after making the repair.

3. Mark the bolt locations. After nailing the splint board to the cracked rafter use a magic marker to mark the planned location of bolts. Measure up from the bottom edge of the splint board a distance of 1 inch and down from the top edge of the splint board 2 inches; draw parallel lines the length of the splint board at these points.

Next, beginning at one end of the splint board, measure along each line 4 inches and place a small 'X' with the magic marker; continue measuring and making X's every 4 inches until the lines have been completely marked.

4. Drill bolt holes and install bolts. Once the bolt locations are marked, use a electric drill and 5/16-inch bit to drill holes through both the splint board and cracked rafter. Place a ¼-inch washer on each bolt, followed by a 1-inch fender washer and slide the bolt through the hole until it protrudes through the other side. Place another ¼-inch washer on the bolt followed by another 1-inch fender washer and screw a nut on to the bolt to hold the hardware together.

Hold the hex head of the bolt steady with an adjustable wrench, and use a ratchet and socket set to tighten the nut onto the bolt. Continue tightening until the fender washers begin to press into the boards, but do not overtighten. Install all bolts, washers and nuts in the same manner for each of the holes.

5. Remove the alignment board. After finishing, remove the 2x4 board used to push the cracked rafter in place.