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What is a Ceiling Joist?

By Eric Tallberg
Updated: May 16, 2024

The ceiling beam, or ceiling joist, has two prime functions. The first is to tie the walls of a structure or a room together, effectively completing a box configuration. The second is, as the name implies, to support the ceiling of the structure, or room. Ceiling joist framing is undertaken after the walls are erected.

Ceiling joists are a number of horizontal beams, running parallel from one wall to the opposite wall of the structure. The beams are attached to the top of the wall at what’s known as the wall plate. A ceiling joist at the top floor of a structure may also support a flat roof, as well as the ceiling. If the roof of the structure is sloped, or pitched, each joist support is attached to a roof rafter, the angled roof support beams. This joist-and-rafter configuration prevents the sloped roof construction from pushing the walls of the structure outward.

Roof trusses are triangular forms used in construction of sloped roofs, and basically consist of rafters and ceiling joists pre-constructed as a unit. Obviously, this saves the extra labor, and expense of erecting each rafter and joist individually. The triangular shape of the truss has long been proven the strongest roofing configuration as far as structural load-bearing capability is concerned.

Typical ceiling joists used in home construction are made of wood, and often called stud joists. There are, however, metal versions, usually manufactured from steel or iron, for use in larger, sturdier structures, such as manufacturing plants, or skyscrapers. Joist sizes and construction are determined by the load the joist is to carry. In most cases, joists, like framed walls, are spaced 16-inches (40.64 cm) apart, or on center.

Ordinarily, a ceiling joist will run in the same direction as the roof rafters. There are, of course, circumstances where parallel construction of joists and roof rafters is not feasible or practical, either due to the design of a structure, or for reasons of expense or aesthetics. In such cases, the joists will run at a 90 degree angle to the rafters, and ties are used, in a manner similar to the parallel joist construction, to strengthen the room or building by binding the tops of the walls.

Ceiling joists are very often not long enough to span an entire structure. In such cases, the joists must be overlapped by some four to six inches (10.16 cm to 15.24 cm), at the point of interior support, such as an interior wall or column. Additionally, they may be attached to the roof rafters directly, or butted against the wall plate using hangers firmly attached to both joist and wall plate.

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Discussion Comments
By anon247063 — On Feb 12, 2012

I am trying to install a lightweight shop light for indoor growing plants. I am having trouble locating a ceiling joist to put in my screw to hold lite from a light chain. How do I find the joist? The light is four feet across.

By anon224658 — On Oct 24, 2011

I need to hang a rack from the ceiling of my garage. I've located (I think) the ceiling joists into which I will attach this rack. However, small test drill holes seem to strike metal, then puncture and go on through the metal. An electrician working in the attic told me that there are metal spacers between the ceiling drywall and the joists. What are these spacers and why are they there? With this in mind, how should I anchor something on the ceiling?

By abiane — On Jul 24, 2010

@pleats - gregg1956 is right. However, an aspect that we haven't looked at is that if ceiling joists aren't properly installed not only can it ruin the house or room, but also the structure as a hole.

Another aspect to think about in regards to the experience level of your brother is that you will need to have this type of work inspected. This is most likely why gregg1956 recommends contracting the work out - aside from the safety of your brother who may or may not be inexperienced.

By gregg1956 — On Jul 24, 2010

@pleats -- Your brother should first consult an engineer or architect with home design experience to measure your space and calculate the appropriate number of joists and distance between them.

They can also tell him what the best kind of wood, etc. is to use.

He should then install them, making sure that they sit appropriately on top of the wall plate.

Finally, he should install bridging between the joists to stiffen them and keep them solid.

I would recommend that if your brother is not very experienced with construction though, that he contract this and other more complicated jobs out to make sure the house is solid and safe.

By pleats — On Jul 24, 2010

Does anybody have some tips on good ceiling joist installation?

My brother is building a house and is trying to do as much of it as possible himself.

What are the tips and tricks for getting good stable ceiling joists?

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