What Is a Ceiling Joist?

A ceiling joist is a structural member used in building the frame of a house or building. It provides a means of support for the materials used for the ceiling surface, such as panelling or drywall. A joist can be constructed of different materials, either wood or metal, depending on the type of structure in which the joist is placed.

Ceiling Joist Description

A ceiling joist is basically a beam, or plank. The specific size of it varies with the weight it will carry, which depends on the weight of the ceiling's surface materials and the weight of any insulation. The ceiling joists also serve as floor joists for the attic and must support anything stored in the attic. Joist size is also dependent on how much of a span the joist will cover, going from one wall to the opposite wall. Joists are often positioned to span the distance of the walls that are closer together in a room to reduce the needed size of the joists.

Differences in Material

The ceiling joists in houses are usually made of different material than those used in the construction of buildings. In houses, the joists are often wood beams, enough to support the ceiling weight. However, in larger structures, such as a tall building or an industrial plant, the ceiling joists are usually made of a metal such as steel to provide the structural strength that is needed.

Joist Placement

The joists are spaced horizontally, normally at a distance of 16 inches apart, but are sometimes spaced with a distance of 24 inches between each joist. This distance is measured from the centre of one joist to the centre of the next joist. They are installed so that they run in the same direction as the roof rafters above them unless design considerations call for them to run at a right angle to the rafters and also to other joists. The outside end of each joist is attached to the heel of the rafter and also to the wall plate.

Two-Story Homes

Floors also have joists, just like ceilings. Floor joists support the weight and foot traffic that the floor endures, just as ceiling joists support the ceiling's weight. In a two-story home, the floor joists that run underneath the second-story floor serve a double-duty and function also as the ceiling joists for the first floor. These joists should be installed so that they adequately support both the floor above and the ceiling materials below them.

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About the Author

Christopher John has been a freelance journalist since 2003. He has written for regional newspapers such as "The Metro Forum" and the "West Tennessee Examiner." John has a Bachelor of Arts in journalism from Memphis State University.