Which Way Do Ceiling Joists Run In My Garage? (What You Need To Know)

When you’re planning to hang some new shelves in your garage you need to know where to attach them. There are plenty of DIY projects where you need to know which way your ceiling joists run. Here’s what you need to know.

Ceiling joists in a garage run from eave to eave if the roof is peaked. However, there are a couple of different ways that joists can run. It is not always apparent unless you can see them.

That said, it can be pretty simple to answer which ways do ceiling joists run in garage roofs when you know what to look for. Below, I will detail the usual directions joists run, why that is, and how to figure out which way yours run.

Which way do ceiling joists usually run?

Ceiling joists will almost always run one of two ways:

From eave to eave
Parallel to the shortest wall

As I mentioned above, one of the standard joist layouts is eave to eave. This layout will have the joists run parallel to the rafters or trusses. The joists will form the base of a triangle with the beams of the rafters or trusses forming the other two sides.

Another common layout has the joists running the shortest distance between two walls. This layout may end up being the same as the previous, but not always. If the garage is perfectly square it will not affect anything. If it is instead rectangular, chances are the joists are parallel to the shorter walls.

Since nothing is constant in this world, these two standard layouts may conflict with each other. Sometimes the ceiling joists will run parallel with the longer walls if the rafters do the same. Ceiling joists can even run perpendicular to the rafters. Unless you can see the joists it is best not to assume, especially in older homes.

Why is that standard?

Ceiling joists are often used as rafter ties which means they need to be laid out in a particular way. Eave to eave joists or joists that are parallel to the rafters serves an important job for the roof. These joists help support the load-bearing walls. Without this support, the roof would eventually push the walls out.

When joists run the shortest distance between two walls it is usually in an effort to reduce material costs. This is particularly common in houses built during lumber shortages. These joists may still serve as rafter ties, but not always.

As you can see, these two reasons are compelling reasons for the frequency of these layouts. Any other design choices may have less obvious reasons behind them.

How to find out which way your ceiling joists run

If the ceiling joists are hidden in your garage there are four good methods to figure out which way they run. Which one you choose is up to you. Certain methods may be harder for you depending on the type of ceiling covering the joists.

electronic stud finder
Use a magnet
Use a nail
Knock and listen

Let’s go over each option.

Use an electric stud finder

This is certainly the easiest method. However, if you do not have a stud finder and do not want to purchase one the others will be better. Stud finders that measure the density–and therefore can find the center of a joist–are best.

Start on one of the shortest walls or one of the sides the eaves are on. Then simply move the stud finder away from that wall on the ceiling and mark where it lights up. If you do not detect any joists after 16 or 24 inches change starting walls.

Magnet

Some stud finders use magnetism to find nails and screws in studs. These are less exact, but function. If you don’t have a stud finder of either type you can simply use a magnet. The stronger the magnet the more reliable it is.

Just like using a stud finder, start on either one of the shortest walls or one of the eave sides. Move the magnet along the ceiling until it pulls on a nail or screw. If you do not detect anything after 16 or 24 inches switch to an adjacent wall.

Nail

If you are reasonably sure you know where the joists are you can use a nail. Obviously, you should be comfortable making a few extra divots in your ceiling for this method. Make sure there aren’t any wires or pipes above your garage that you could damage.

Using a hammer and a nail, lightly tap the nail into the ceiling where you believe the joist is. If you feel little resistance you have missed. If you meet resistance you have found a joist.

Knock and listen

On the far side of low tech is simple knocking. This method won’t work very well if you have a rough-textured ceiling.

For this method knock on the ceiling and listen to how it sounds. If your knocking sounds hollow you’re between joists. If it sounds more solid you have found one. As with the other methods, start with one wall and move away from it. If that turns up nothing, switch walls.

Final thoughts

Now you know which way ceiling joists run in your garage. As one last tip, know that most of the time joists throughout the house run the same way. If you can see joists in another part of your home chances are your garage joists run the same way.

Frequently Asked Questions

How far apart are joists in a garage ceiling?

Ceiling joists are usually either 16” or 24” apart on center. This distance will be the same for each joist.

Do ceiling joists run parallel to floor joists?

Ceiling and floor joists will often run parallel to each other. They do not have to, however.

What is the difference between a ceiling joist and a floor joist?

Both types of joists are very similar. The main difference is that floor joists support the floor, walls, and ceiling. Ceiling joists usually do not support the floor.

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Which Way Do Ceiling Joists Run In My Garage? (What You Need To Know)