How to Splice a Ceiling Joist

Broken or extra-long joists need reinforcing.
Broken or extra-long joists need reinforcing. (Image: Hans Hansen/Lifesize/Getty Images)

Ceiling joists may need splicing if they have been cracked during transport or construction. They might also be spliced if a piece has been cut out of one during prior renovations or if a very long joist is needed and you need to build it out of more than one piece of wood. When properly constructed, a joist splice can be virtually as strong as a solid piece of wood.

Things You'll Need

  • Two pieces of 2-by-4 lumber, 48 inches long
  • Construction adhesive
  • Screws, 4 inches long
  • Drill

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Spread construction adhesive onto one face of each of the two 2-by-4s.

Place one of the 2-by-4s on the side of the joist that is being spliced. Center the 2-by-4 over the crack or break in the joist. Tack the 2-by-4 down by putting a 4-inch-long screw into each end. Drive the screws in far enough to hold the 2-by-4 to the joist, but not so far in that they go through the other side of the joist.

Put the second 2-by-4 on the other side of the joist so the joist is sandwiched between the two 2-by-4s. Screw this 2-by-4 to the joist with 4-inch-long screws, driving the screws all the way in so that they go through the 2-by-4, through the joist and into the opposite 2-by-4.

Go back to the first two screws you drove in and finish driving them in so they go through the joist and into the second 2-by-4.

Add more screws along the length of both 2-by-4s. The more screws you put in, the stronger the splice will be.


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