How to Build a Ceiling Joist

Where a single joist is not strong enough to support the ceiling, create a sandwiched ceiling joist by placing a piece of plywood between two pieces of dimensional lumber. The plywood provides strength and stiffness. The dimensional lumber keeps the plywood from bending. For the strongest ceiling joist, add a piece of steel flashing on either side of the plywood core. The dimensional lumber will keep the steel from buckling. Along with the construction adhesive that holds the entire apparatus together, it binds all the parts into a single whole. Keep the beam together as one unit by bolting it with machine screws and fastener nuts.

Two lengths of 2-by-10-inch dimensional lumber
3/4-inch plywood the same length as the dimensional lumber
Two pieces of steel flashing the same length as the dimensional lumber
Construction adhesive
Drill
4-inch long, 1/4-inch diameter bolts with nuts
Torque wrench

Instructions

- 1
  Lay one of the 2-by-10-inch boards flat on the floor. Apply construction adhesive 1 inch from every edge and in a zigzag pattern on the rest of the beam.
- 2
  Press a piece of steel flashing into the adhesive, making sure the edges of the steel line up with the edges of the board. Apply construction adhesive to the steel flashing in the same pattern that you used when applying the adhesive to the 2-by-10-inch board.
- 3
  Lay the piece of plywood on top of the steel flashing, lining up the edges. Press the plywood firmly into the steel. Apply construction adhesive to the plywood using the same pattern of application as on the steel flashing.
- 4
  Press a piece of steel flashing into the adhesive on the plywood. Line up its edges with the edges of the rest of the components. Put construction adhesive onto the steel flashing, using the same outline and fill used on the rest of the layers.
- 5
  Lay the final piece of 2-by-10-inch dimensional lumber on top of the steel flashing, pressing it in place so the adhesive grabs it. Line up the edges.
- 6
  Drill holes 12 inches apart in a diamond pattern, drilling completely through the laminated joist.
- 7
  Insert bolts into the predrilled holes and secure each bolt with a nut. Use a torque wrench to tighten the nuts securely.

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