How to Keep a 2x4 From Sagging

Examine each 2-inch-by-4-inch framing member to see if the board is crowned or bowed. This needs to be done before the board is installed. The best way to do this is to set the far end of the board on the ground or a work desk and then hold the near end just a few inches in front of your eyes. Now look down the length of the 2-inch-by-4-inch board, so that you can observe the entire length at once. If one edge of the board is curved outwards, then put that board into the ceiling structure with the curved side facing up. The weight of the ceiling might counteract the natural bow in the board. If the curve is really drastic, then throw the board out.

Change the spacing of the 2-inch-by-4-inch boards. The 2-inch-by-4-inch boards need to be set in place together. Sixteen inches on center should work with most ceilings, but 24 inches on center can be changed to 16 inches on center spacing. This means that the center of the first 2-inch-by-4-inch foot board gets placed 16 inches from the edge of the room and the center of the second framing member is located at 32 inches. All along the width of the ceiling, the measurement from the center of one 2-inch-by-4-inch joist to the next should be 16 inches.

Add blocking between the individual units of the ceiling frame. Do this by measuring the distance between two framing members with a tape measure and then making the cut with a circular saw and speed square on the saw horses. Be sure to wear safety goggles. Then nail the piece between two ceiling boards using the No. 12 resin-coated common nails and framing hammer. If your 16-inch-on-center ceiling frame is correctly installed, each reading should be very close to 14 1/2 inches.

Make a built-up ceiling joist by placing a second 2-inch-by-4-inch board against another 2-inch-by-4-inch ceiling board. First measure the length of the existing board in the ceiling. Then cut a second board to that exact length using the circular saw. Next apply construction adhesive to one side of the existing ceiling board. Finally, nail the new board right into the old one. Be sure to to hammer a few nails into the support wall for the 2-inch-by-4-inch ceiling. This method can be used successfully to strengthen a cracked or weak ceiling board, or to strengthen one particular 2-inch-by-4-inch board so it will safely support a ceiling fan.