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Blocking a Ceiling Joist

Ceiling joists span from wall to wall, providing the base of the roof structure, in addition to being used to support ceiling lights and to attach drywall. In specific instances, such as the installation of a return air duct, a recessed can light or stovepipe, you may have to insert joist blocking to control airflow or to keep insulation away from a hot can or pipe. Blocking a ceiling joist is a relatively simple project.

Step 1

Measure the space between the two ceiling joists. If the joists sit on 16-inch centers, meaning it’s exactly 16 inches from the center of one joist to the center of the next joist, the space between the joists will be 14 1/2 inches. For joists on 24-inch centers, the space between the joists is 22 1/2 inches.

Step 2

Cut a board to match the measurement. To create a full block between the two joists, the board should be the same dimension as the joists. For example, if the joists are constructed from 2-by-10s, use a 2-by-10 for the block. In some instances, a 1-by-10, or a piece of drywall, cut to the same dimension, suffices. If possible, though, opt for same-size dimensional lumber.

Step 3

Position the cut board sideways, between the two joists, and secure it with two 12d nails, inserted from the outsides of the supporting joists, into each end of the board. Space the nails evenly. Because you're driving the nails in a restricted space, a nail gun works better than a hammer.

Warning

  • If the ceiling contains trusses and not joists, do not install blocking without first consulting an engineer or the truss manufacturer.
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