Ceiling joists are not the same size as floor joists and they are designed more as a weight transfer and distribution system more than they are a load-bearing system. At the end of the day, it’s difficult to be precise considering the amount of weight a joist can hold or how strong it is overall.
The size of the joists and how they are designed in relation to the rafters and load-bearing walls determine their strength. If you’re thinking about hanging something on a ceiling joist, it must be limited to 50lbs unless you know otherwise.
The typical size of joists that can withstand 50lbs of pull-down weight are 2×6 joists. There are solid lumber joists and I-Beam joists with the former being the most popular. I-Beams are still ceiling joists. They are just designed differently, with perpendicular wood pieces between them, extending their length.
How to Determine What Your Joists Can Hold
If you’re thinking about hanging something on a joist, it’s important to consider the “where” as much as it is the strength of the joist. The farther out towards the center of the joist you move, the less supportive it will be.
For example, fill a glass full of water and hold it out in front of you as far as your arm will extend, elbow locked. It gets heavy quickly and it also feels heavier the more you extend your arm out. Set the same glass on your bicep, with your arm extended, and the weight is much more manageable.
The same holds true for a joist, with its weakest point located at the point that is equally distant from the beam and the exterior, load-bearing wall.
Check the Joists from the Attic
If you’re looking to hang something from a joist, it’s a good idea to go up into the attic and have a look at what you will be working with. It’s entirely possible that you will find joists running across that are sandwiched together to form two or even three joists for a particular reason.
These are going to be the strongest of the joists in your overhead and that’s where you want to hang something from. These “joist rails,” as they are called, are designed to hold the extra weight. That’s the only reason why you would find multiple joists locked together.
You want to avoid the longest, single joists that you find in the attic. While they may not break under the weight you apply to them, they could sag, creating cracks in your ceiling’s sheetrock.
Apply Weight on the Edges
In the above analogy, we explained how much harder it is to hold a glass of water fully extended from the body than it is to balance a glass of water on your bicep. If you want to hang plants or even a boxing bag from one of your joists, it’s better to stick to the edges.
The center of gravity and the strength of a joist are more prevalent on the edges and the joist is more likely to accommodate the weight of whatever you want to hang there. One of the most common reasons for joist failures is a flaw in the structure.
Just because expert contractors built your home, doesn’t mean they are impervious to mistakes, and it’s quite common for a joist to collapse and the ensuing investigation to determine that the joist was improperly placed. Or, it could be that there is an issue with accompanying structures as well.
How Big are Standard Ceiling Joists?
For the most part, your ceiling joists are going to be 2×6 joists. That’s not always the case, but it’s what you will find the vast majority of the time. The exceptions usually boil down to various, uncommon designs.
In some cases, only 2×4 joists are used. This happens in smaller buildings, like single-bedroom homes with very simple architecture, exterior garages, or exterior shed buildings.
It’s also common to use 2×4 joists to design higher ceilings. Since ceiling joists are laid down vertically, the less width they have allows contractors to raise the ceiling a little higher. It’s far more common to see a wide variety of joist sizes if you are looking at much older homes.
More modern homes are fiercely regulated and it’s very difficult or requires very specific reasoning to go outside of the general framework for constructing new homes today. If you venture into a home with very low ceilings, you shouldn’t be surprised if you find 2x12s in the overhead.
With much wider ceiling joists, the height of the ceiling is more limited and usually means constructing a lower ceiling. Also, in older homes, it’s more common to see a degree of sag from the ceiling joists.
That’s mostly due to there being fewer codes to comply with when the home was originally constructed. The joists might be too far apart or too long without accompanying structural support.
Ceiling joists are also just as prone to rot, if moisture can reach them in any way, as any other piece of exposed, untreated lumber.
Lumber Grade
This is the last piece of information that you need to determine the strength of your joists. It’s not an easy piece of information to find either. It’s not as if they stamp the lumber grade on each piece so you can easily see it while rooting through attic insulation.
Softwood and hardwood are the two primary components of what constitutes a “lumber grade.” You’re far more likely to find soft wood, such as pine, spruce, or cedar, in your ceiling joists than hardwood.
Hardwoods are generally reserved for floor joists and are made out of hickory, oak, walnut, and birch. Softwood will not support a high amount of weight like hardwood will.
Conclusion
As you can see, there are several factors that go into determining the strength of your ceiling joists. It’s not just an open and shut case with an easy answer. You will need to be willing to do some investigation of your own. In the meantime, only hang heavy items or equipment at the edges, and avoid getting too crazy with it.
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