Reinforcing the Ceiling

Install jack posts if necessary to remove any existing sag in the ceiling. Place the posts on top of a large board or piece of plywood on the floor. Put the base of the post directly over a floor joist. Place another board or piece of plywood between the top of the post and the ceiling, and turn the bolt on the post to sandwich the board between the top of the post and the ceiling. Turn the top bolt of the jack to raise its top until the ceiling has returned to a flat, non-sagging condition.

Lay a 2-by-4 in the attic, flat on top of the ceiling joists so that it crosses the joists at a right angle and extends from wall to wall. Secure the 2-by-4 to the joists by driving 4-inch-long screws through the 2-by-4 and into the joists.

Lay a 2-by-6 next to the 2-by-4, with the 2-by-6 on edge so its six-inch dimension is vertical. Secure the 2-by-6 to the 2-by-4 by driving 4-inch-long screws through the side of the 2-by-6 and into the 2-by-4.

Measure the distance from the tops of the ceiling joists to the underside of the roof immediately above them. Cut several 2-by-4s to these lengths and install them vertically so that they extend from the 2-by-6 that you just installed to the rafters above. Screw the ends of these 2-by-4s to the 2-by-6 at the bottom and the sides of the rafters at the top, using four-inch-long screws. These 2-by-4s will function as joist hangers, reinforcing your ceiling and preventing it from sagging.

Remove the jack post by turning the bolt counterclockwise, being careful to keep hold of the board that's between the jack post and the ceiling so it doesn't fall on your head.